RESULTS


      In the sections below we present the HRV results pertaining to each disturbance process, cover type, habitat of special interest, and wildlife indicator species. Results pertaining to HRV departure (i.e., Fire Regime Condition Class) are included in theses sections where appropriate. In addition, we present the results pertaining to the effects of scale (i.e., landscape extent) and landscape context (i.e., location) on landscape structure, wildlife habitat, and HRV departure.

 

    Disturbance Processes & Dynamics

    Vegetation Patterns & Dynamics

    Habitats of Special Interest

    Wildlife Indicator Species

    Effects of Scale and Context

    Historic Range of Variability Tables


Disturbance Processes & Dynamics


      This report focuses on the effects of two major natural disturbances: wildfire and insects/diseases; the impacts of other natural disturbances during the reference period were likely localized in time or space and therefore probably had far less impact on vegetation patterns over broad spatial and temporal scales than did fire and insects/diseases. In the sections below, we briefly describe the simulated disturbance regime (i.e., spatial extent and distribution, frequency and temporal variability) associated with each of these disturbance processes. In these sections, we refrain from describing variations among vegetation types - this will be accomplished in the section on Vegetation Patterns and Dynamics. In addition, although each disturbance process is discussed separately, reflecting the fact that each disturbance process was implemented as a separate process in RMLANDS, the model did allow for synergisms and feedbacks among disturbances (see RMLANDS - Model Parameterization). Finally, it is important to realize that while the information below is presented as “results”, it could have easily been presented in the methods section as “model calibration”. Key spatial and temporal aspects of the disturbance regime were evaluated during preliminary “calibration” runs, and subsequent adjustments were made to model parameters to effect desired changes. Thus, while the information presented below does in fact represent results (output) of the simulation, it also represents a set of targets used to calibrate the model (i.e., adjust model parameters to achieve desired results). While this may seem a bit circular, it was a necessary process for a complex model such as RMLANDS. Plus, our real emphasis was on quantifying the vegetation patterns and dynamics resulting from these disturbance processes.


Wildfire


      Roughly 96% of the landscape (817,597 of 847,638 ha) was eligible for wildfire disturbance, and this included all vegetated cover types and successional stages despite their pronounced variation in susceptibility to wildfires. As expected, the frequency and extent of simulated wildfires varied markedly among decades (Figure-frequency, Figure-extent). On average, once every two decades, >10% of the eligible area was burned, and roughly once every 120 years, >20% was burned (Figure-recurrence), inclusive of both high- and low-mortality affected areas. Under an extreme case from a single simulation run, the total area disturbed in a single decade was 211,127 ha (26% of eligible area)(Figure-map). This was the result of many individual fires, including a few very large fires (>50,000 ha) and many intermediate and small fires. In addition, the majority of the area disturbed was from low-mortality fire burning principally through low-elevation ponderosa pine and warm dry mixed-conifer forest types.

 

Wildfire Movie - Click here to view a movie depicting wildfire disturbances on the San Juan National Forest over an 800-year (10-year time steps) simulation representing the reference period disturbance regime. NOTE, this is a 38 Mb Microsoft Media file (.avi) that requires appropriate movie viewing software (e.g., Quick Time Player).


      As expected (given the model structure), the variation in frequency and extent of wildfires was strongly related to climate (Figure-initiations, Figure-extent). It is worth noting that while the number of wildfire initiations was strongly and linearly related to the climate modifier (representing, in this case, the average drought index), the total area disturbed was much less so. This reflects that fact that while wildfires were much more likely to start during drought periods, they were not always guaranteed to expand into large fires. Thus, even under drought periods, there were many decades in which fires burned relatively little area. However, all decades in which wildfires burned >20% of the eligible landscape were during droughts (i.e., climate modifier >1), and the most extreme decade of burning (~ 34% of eligible) was during the most extreme drought (climate modifier = 1.43).


      Under this wildfire regime, the return interval between fires (of any mortality level) varied widely across the forest from 19 years to >800 years, although only a negligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, there was a distinct spatial pattern of variation in return intervals (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. Overall, the wildfire rotation period for the eligible area of the landscape averaged 94 years across simulation runs (177 and 201 years for low- and high-mortality wildfires, respectively) and rotation periods were relatively consistent among simulation runs (Table-rotation).


Pinyon Decline


      Less than 4% of the landscape (30,878 of 847,638 ha) was eligible for pinyon decline disturbance, and this included all cover types containing the host species (Pinus edulis). The host cover types were relatively scarce and patchily distributed within the boundaries of the project area and existed at the upper elevations of their natural distributions, and this clearly influenced the disturbance regime. As expected, the frequency and extent of simulated pinyon decline varied markedly among decades (Figure-frequency, Figure-extent). Major epidemics were relatively infrequent and distinctly episodic in occurrence. In most decades <1% of the host area was affected by an outbreak; however, roughly once every 200 years a major epidemic affecting >20% of the host area would occur (Figure-recurrence). The frequency of these major outbreaks was highly variable among simulation runs. Under an extreme case from a single simulation run, the total area disturbed in a single decade was 21,311 ha (69% of eligible)(Figure-map). Typical of other major outbreaks, in this case disturbance patches coalesced into extensive areas covering much of the host distribution, although there were noticeable gaps of significant extent that were not disturbed, and the majority of the disturbance was low mortality due to the immunity of the co-dominant juniper component of the host forest types (pinyon-juniper woodlands).

 

Pinyon Decline Movie - Click here to view a movie depicting pinyon decline epidemics on the San Juan National Forest over an 800-year (10-year time steps) simulation representing the reference period disturbance regime. NOTE, this is a 30 Mb Microsoft Media file (.avi) that requires appropriate movie viewing software (e.g., Quick Time Player).


      As expected (given the model structure), the variation in frequency and extent of epidemics was strongly related to climate, although the relationship was much stronger for the number of initiations (Figure-initiations) than the area disturbed (Figure-extent). The area disturbed exhibited somewhat of a threshold relationship with climate (representing, in this case, the cumulative consecutive years of drought index), whereby epidemics affecting a substantial proportion of the host area occurred only during decades with a drought index > 1, but the magnitude (area disturbed) of epidemics varied dramatically in relation to the climate index above this threshold. This reflects that fact that while major epidemics were limited to periods of extended drought, local outbreaks during such periods were not always guaranteed to expand into major epidemics. Thus, even under extended drought conditions, there were many decades in which pinyon decline affected relatively little area. Nevertheless, the most extreme decade of pinyon decline (~ 70% of eligible) was during the most extreme extended drought (climate modifier = 1.98).


      Under this pinyon decline disturbance regime, the return interval between outbreaks (of any mortality level) varied widely across the forest from 80 years to >800 years, although on average >10% of the host area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, the spatial pattern of variation in return intervals reflected the somewhat patchy and disjunct distribution of the host cover types (Figure-map). Specifically, return intervals increased with the degree of patch isolation; smaller, disjunct and more isolated patches of the host cover type exhibited much longer return intervals than average. This can be attributed to the decreased effectiveness of spread into these patch of outbreaks initiated elsewhere in the landscape. Overall, the pinyon decline rotation period for the eligible area of the landscape averaged 466 years across simulation runs (549 and >3000 years for low- and high-mortality disturbances, respectively); however, the observed rotation periods were highly variable among simulation runs (Table-rotation). This variability was due in part to the relatively infrequent and episodic nature of the outbreaks, but it was also due in large part to the relative scarcity and disjunct distribution of the host cover types within the project area. In reality, the pinyon decline disturbance regime is probably strongly influenced by what happens throughout the core of the distribution of the host, which happens to fall principally outside the project boundary. Consequently, these results should be viewed with caution.


      Not surprisingly, the simulated landscape susceptibility to pinyon decline fluctuated over time in response to changing climatic conditions and vegetation conditions. The coefficient of variation in landscape susceptibility was 59%, and this was the highest variability for any of the simulated insects/pathogens (Table-hrv-susceptibility). Based on the available vegetation data, the current landscape is in a state of relatively high susceptibility compared to the simulated HRV. Overall, the current landscape condition falls at the 91st percentile of the HRV distribution (i.e., 62% departure index) and the magnitude of departure varies spatially across the forest (Figure-susceptibility map). However, given the lack of reliable field data on current stand age and condition in this cover type, these findings must be viewed with caution. Yet, observations of the recent extreme pinyon decline in the project area and surrounding region seem to substantiate our findings.


Pine Beetle


      Roughly 24% of the landscape (201,197 of 847,638 ha) was eligible for pine beetle disturbance, and this included all cover types containing the host species (Pinus ponderosa). As expected, the frequency and extent of simulated pine beetle epidemics varied markedly among decades (Figure-frequency, Figure-extent). In most decades, pine beetles were at endemic levels (i.e., no epidemic). However, 1-3 times per 100 years an epidemic occurred. On average, once every 100 years an epidemic affecting >10% of the host area would occur, and roughly once every 400 years a major epidemic affecting >20% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. Under an extreme case from a single simulation run, the total area disturbed in a single decade was 50,688 ha (25% of eligible)(Figure-map). Typical of other major outbreaks, in this case disturbance patches of widely varying sizes up to roughly 200 ha were widely dispersed across the forest, but were more concentrated in some areas, and the majority of the disturbance was low mortality.

 

Pine Beetle Epidemics Movie - Click here to view a movie depicting pine beetle epidemics on the San Juan National Forest over an 800-year (10-year time steps) simulation representing the reference period disturbance regime. NOTE, this is a 41 Mb Microsoft Media file (.avi) that requires appropriate movie viewing software (e.g., Quick Time Player).


      As expected (given the model structure), the variation in frequency and extent of epidemics was strongly related to climate (Figure-initiations, Figure-extent). The area disturbed exhibited a positive and relatively linear relationship with climate (representing, in this case, the cumulative consecutive years of drought index). Interestingly, extreme drought decades (climate modifier = 1.98) always resulted in fairly major epidemics affecting 12-25% of the host area, but there was considerable variation in the magnitude of epidemic for decades with moderate or mild droughts.


      Under this pine beetle disturbance regime, the return interval between outbreaks (of any mortality level) varied widely across the forest from 50 years to >800 years, although on average ~10% of the host area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). There did not appear to be any predictable spatial pattern of variation in return intervals (Figure-map). Instead, the pattern seemed somewhat random, suggesting that it was largely chance that determined which areas got disturbed more frequently than others. This was somewhat borne out by the lack of strong correlation among separate simulation runs in the spatial pattern of variation in return intervals. Overall, the pine beetle rotation period for the eligible area of the landscape averaged 306 years across simulation runs (377 and 1,617 years for low- and high-mortality disturbances, respectively), and rotation periods were relatively consistent among simulation runs (Table-rotation).


      The simulated landscape susceptibility to pine beetle outbreaks fluctuated over time in response to changing climatic conditions and vegetation conditions, although the variability was remarkably low; the coefficient of variation in landscape susceptibility was only 15% (Table-hrv-susceptibility). The low variability was likely due to the relatively poor representation and low variability over time of the most susceptible stage of stand development, the stem exclusion stage, in the host cover types. Based on the available vegetation data, the current landscape is in a state of extremely high susceptibility compared to the simulated HRV. Overall, the current landscape condition falls well outside the HRV distribution (i.e., 100% departure index) and the magnitude of departure varies spatially across the forest (Figure-susceptibility map) The current state of departure appears to be due to the preponderance of stands in the stem exclusion stage - the most susceptible to pine beetle outbreaks - and the paucity of stands in the fire-maintained open canopy stage, which have a relatively low susceptibility to pine beetle outbreaks.


Douglas-fir Beetle


      Roughly 25% of the landscape (210,135 of 847,638 ha) was eligible for Douglas-fir beetle disturbance, and this included all cover types containing the host species (Pseudotsuga menziesii). As expected, the frequency and extent of simulated Douglas-fir beetle epidemics varied markedly among decades (Figure-frequency, Figure-extent). In most decades <1% of the host area was affected by an outbreak; however, at least once every 100 years an epidemic affecting >2% of the host area would occur, and roughly once every 400 years an epidemic affecting >4% would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. Under an extreme case from a single simulation run, the total area disturbed in a single decade was 13,094 ha (6% of eligible)(Figure-map). Typical of other major outbreaks, in this case disturbance patches of widely varying sizes up to roughly 100 ha were widely dispersed across the forest, but were more concentrated in some areas, and the majority of the disturbance was low mortality.


      By design, the variation in frequency and extent of Douglas-fir beetle epidemics was not related to climate. It was determined that climate is not a major factor controlling the spatial and temporal occurrence of outbreaks. Instead, it was determined that variation is driven more by changes in population demographics (e.g., changes in reproduction and survival due to predators and parasitoides) and interactions with other disturbance processes (e.g., spruce budworm outbreaks, wildfires, and windthrow). Consequently, aside from the explicit interactions with spruce budworm outbreaks and wildfires, we treated these other factors as a source of random variation.


      Under this Douglas-fir beetle disturbance regime, the return interval between outbreaks (of any mortality level) varied widely across the forest from 80 years to >800 years, although on average the majority of the host area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As might be expected, given the relatively minor extent of disturbance, there did not appear to be any predictable spatial pattern of variation in return intervals (Figure-map). Instead, the pattern seemed more or less random, suggesting that it was largely chance that determined which areas got disturbed more frequently - or even at all - than others. This was somewhat borne out by the lack of strong correlation among separate simulation runs in the spatial pattern of variation in return intervals. Overall, the Douglas-fir beetle rotation period for the eligible area of the landscape averaged 1,192 years across simulation runs (1,300 and 14,300 years for low- and high-mortality disturbances, respectively); however, as might be expected given the relatively low level of disturbance, the observed rotation periods were highly variable among simulation runs (Table-rotation).


      The simulated landscape susceptibility to Douglas-fir beetle outbreaks fluctuated over time in response to changing vegetation conditions and interactions with other disturbance agents (specifically, spruce budworm epidemics and wildfires), although the variability was remarkably low; the coefficient of variation in landscape susceptibility was only 12%, the lowest of any of the simulated insects/pathogens (Table-hrv-susceptibility). The low variability was likely due to the preponderance of late-successional stands (all highly susceptible to outbreaks) in the host cover types maintained over time during the reference period. Based on the available vegetation data, the current landscape is in a state of moderately low susceptibility compared to the simulated HRV. Overall, the current landscape condition falls at the 26th percentile of the HRV distribution (i.e., 0% departure index), although the magnitude of departure varies spatially across the forest (Figure-susceptibility map) The current state of relatively low susceptibility is likely due to the absence of recent spruce budworm outbreaks or wildfires in the host cover types, which often trigger Douglas-fir beetle outbreaks.


Spruce Beetle


      Roughly 51% of the landscape (431,617 of 847,638 ha) was eligible for Spruce beetle disturbance, and this included all cover types containing the host species (Picea engelmannii); although susceptibility varied dramatically among cover types in relation to the abundance of the host species. As expected, the frequency and extent of simulated spruce beetle epidemics varied markedly among decades (Figure-frequency, Figure-extent). In most decades <1% of the host area was affected by an outbreak; however, 1-2 times per 100 years a major epidemic affecting >10% of the host area would occur, and roughly once every 400 years a major epidemic affecting >25% would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. Under an extreme case from a single simulation run, the total area disturbed in a single decade was 115,458 ha (27% of eligible)(Figure-map). Typical of other major outbreaks, this outbreak consisted of a single, large, contiguous disturbance patch of up to ~100,000 ha, plus a number of smaller, disjunct patches nearby, with the majority of the disturbance being high mortality.

 

Spruce Beetle Epidemics Movie - Click here to view a movie depicting spruce beetle epidemics on the San Juan National Forest over an 800-year (10-year time steps) simulation representing the reference period disturbance regime. NOTE, this is a 46 Mb Microsoft Media file (.avi) that requires appropriate movie viewing software (e.g., Quick Time Player).


      By design, the variation in frequency and extent of spruce beetle epidemics was not related to climate. It was determined that climate is not a major factor controlling the spatial and temporal occurrence of outbreaks. Instead, it was determined that variation is driven more by changes in population demographics (e.g., changes in reproduction and survival due to predators and parasitoides) and interactions with other disturbance processes (e.g., wildfires and windthrow). In particular, spruce beetle outbreaks often initiate following major windthrow events - which we did not model in RMLANDS. Consequently, aside from the explicit interaction with wildifire, we treated these other factors as a source of random variation.


      Under this spruce beetle disturbance regime, the return interval between outbreaks (of any mortality level) varied widely across the forest from 47 years to >800 years, although on average >25% of the host area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). There was a distinct spatial pattern of variation in return intervals over the course of a single 800-year simulation (Figure-map). Specifically, return intervals generally increased with decreasing elevation, reflecting the increasing scarcity and fragmented distribution of the preferred host species (Picea engelmannii) at lower elevations. In addition, the return interval variation was highly contagious or clumped in distribution, reflecting the chance occurrence of multiple outbreaks in the same area over the course of the simulation. However, it is important to note that this spatial pattern of variation, while consistently contagious among separate simulation runs, also varied somewhat in geographic distribution among simulation runs, reflecting the stochastic nature of where outbreaks occurred. Overall, the spruce beetle rotation period for the eligible area of the landscape averaged 273 years across simulation runs (2,726 and 304 years for low- and high-mortality disturbances, respectively), and rotation periods were relatively consistent among simulation runs (Table-rotation).


      The simulated landscape susceptibility to spruce beetle outbreaks fluctuated over time in response to changing vegetation conditions and interactions with other disturbance agents (e.g., large windthrow events, which we treated as a purely stochastic occurrence in our simulations), although the variability was relatively low; the coefficient of variation in landscape susceptibility was only 22% (Table-hrv-susceptibility). The low variability was likely due to the preponderance of late-successional stands (all highly susceptible to outbreaks) in the host cover types maintained over time during the reference period. Based on the available vegetation data, the current landscape is in a state of extremely high susceptibility compared to the simulated HRV. Overall, the current landscape condition falls at the 99th percentile of the HRV distribution (i.e., 94% departure index), although the magnitude of departure varies spatially across the forest (Figure-susceptibility map) The current state of departure appears to be due to the preponderance of high-elevation conifer stands in the late-seral stages - the most susceptible to spruce beetle outbreaks.


Spruce Budworm


      Roughly 51% of the landscape (431,617 of 847,638 ha) was eligible for Spruce budworm disturbance, and this included all cover types containing the host species (Pseudotsuga menziesii, Abies concolor, Abies lasiocarpa, and Picea engelmannii); although susceptibility varied slightly among cover types in relation to the abundance of the preferred host species (i.e., the true firs and Douglas-fir). As expected, the frequency and extent of simulated spruce budworm epidemics varied markedly among decades, although the relationship was much stronger for the area disturbed (Figure-frequency, Figure-extent). In most decades, spruce budworm populations were at endemic levels (i.e., no epidemic). However, 2-5 times per 100 years an epidemic occurred. On average, once every 30 years an epidemic affecting >10% of the host area would occur, and roughly once every 100-150 years a major epidemic affecting >40% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. In many cases, major epidemics extended over two decades; thus, the maximum area disturbed during a single epidemic was much greater than the maximum area disturbed in any single decade. Under an extreme case from a single simulation run, the total area disturbed in a single epidemic (extending over two decades) was 286,328 ha (66% of eligible)(Figure-map). Typical of other major outbreaks, in this case disturbance patches coalesced into extensive areas covering much of the host distribution, although there were noticeable gaps of varying extent that were not disturbed, and the majority of the disturbance was low mortality.

 

Spruce Budworm Epidemics Movie - Click here to view a movie depicting spruce budworm epidemics on the San Juan National Forest over an 800-year (10-year time steps) simulation representing the reference period disturbance regime. NOTE, this is a 30 Mb Microsoft Media file (.avi) that requires appropriate movie viewing software (e.g., Quick Time Player).


      As expected (given the model structure), the variation in extent of epidemics was strongly related to climate, even though, surprisingly, there was no relationship between climate and frequency of epidemics (Figure-initiations, Figure-extent). The area disturbed exhibited a strong positive and linear relationship with climate (representing, in this case, the cumulative consecutive years of wet index). Interestingly, extremely wet decades (climate modifier = 1.98) always resulted in fairly major epidemics affecting 35-55% of the host area.


      Under this spruce budworm disturbance regime, the return interval between outbreaks (of any mortality level) varied widely across the forest from 33 years to >800 years, although almost no eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). There did not appear to be any predictable spatial pattern of variation in return intervals (Figure-map). Instead, the pattern seemed somewhat random, suggesting that it was largely chance that determined which areas got disturbed more frequently than others. This was somewhat borne out by the lack of strong correlation among separate simulation runs in the spatial pattern of variation in return intervals. Overall, the spruce budworm rotation period for the eligible area of the landscape averaged 103 years across simulation runs (109 and 1,942 years for low- and high-mortality disturbances, respectively), and rotation periods were relatively consistent among simulation runs (Table-rotation).


      The simulated landscape susceptibility to spruce budworm outbreaks fluctuated over time in response to changing climate and vegetation conditions, although the variability was relatively low; the coefficient of variation in landscape susceptibility was only 16% (Table-hrv-susceptibility). The low variability was likely due to the preponderance of late-successional stands containing multiple canopy layers (all highly susceptible to outbreaks) in the host cover types maintained over time during the reference period. Based on the available vegetation data, the current landscape is in a state of extremely high susceptibility compared to the simulated HRV. Overall, the current landscape condition falls outside the HRV distribution (i.e., 100% departure index), although the magnitude of departure varies spatially across the forest (Figure-susceptibility map) The current state of departure appears to be due to the preponderance of conifer stands in the late-seral stages - the most susceptible to spruce budworm outbreaks.



Vegetation Patterns & Dynamics


      We recognized 23 distinct vegetation types ("cover types") on the SJNF and surrounding area for the purposes of RMLANDS simulations (see RMLANDS - Vegetation Classification). However, several of these types were treated as “static” in our simulations; i.e., they did not have separate stand conditions or undergo successional changes, at least over the spatial and temporal scales (e.g., 25-m cell size, 10-year time step) considered in our simulations, even though they may have been subject to one or more disturbance process. For example, mountain grasslands were subject to wildfire but were assumed to remain constant in composition and structure due to the relatively rapid (i.e. 1-2 years) recovery of vegetation following fire. In the sections below, we limit our discussion to only those cover types that we treated as dynamic in RMLANDS. For each of these cover types, we briefly describe the simulated disturbance regime (i.e., spatial extent and distribution, frequency and temporal variability) associated with each relevant disturbance process, the vegetation dynamics resulting from the interplay between these disturbance processes and succession, and we conclude each section with an examination of the cover type’s current departure from the simulated HRV. Lastly, we describe the range of variation and departure of the current landscape in overall landscape structure, in which all cover types and stand conditions are considered jointly as a single patch mosaic.


Pinyon-Juniper Woodland [cover type description]


      Pinyon-juniper woodland is a very uncommon cover type on the SJNF, encompassing 5,023 ha and comprising <1% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in pinyon-juniper woodland varied markedly among decades (Figure-initiations, Figure-extent). In most decades, >5% of the pinyon-juniper woodland burned, inclusive of both high- and low-mortality affected areas, and roughly once per 100 years, >20% of the area burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 23 years to >800 years, with a mean and median of 100 years, and roughly 2% of the area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return intervals varied spatially across the forest (Figure-map), but given the scarcity of this cover type it was impossible to discern whether there were any meaningful patterns.


      The frequency and extent of simulated pinyon decline epidemics in pinyon-juniper woodland varied among decades in an episodic fashion (Figure-initiations, Figure-extent). In most decades, pinyon decline was at endemic levels and <1% of the pinyon-juniper woodland was disturbed. However, roughly once every 200 years an epidemic affecting >20% of the host area would occur, and roughly once every 300-400 years a major epidemic affecting >40% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 89 years to >800 years, with a mean and median of 400 years, although >15% of the eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest (Figure-map), but given the scarcity of this cover type it was impossible to discern whether there were any meaningful patterns.


      The age structure and dynamics of pinyon-juniper woodland reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the pinyon-juniper woodland was >70 years since stand origin, although at any point in time this varied from 22% to 87% (Figure-survivorship). On average, 25% of the pinyon-juniper woodland survived to >160 years, and <1% survived a stand-replacing disturbance for >800 years. Note, the relatively “young” age distribution of this cover type (compared to our expectations for this cover type) was due principally to its landscape position in the project area, where it exists as small disjunct patches at the higher range of its elevational distribution and is juxtaposed to ponderosa pine forests and mountain shrublands - which burned frequently in the simulations. Lower elevation, more extensive pinyon-juniper woodlands just outside the project boundary burned less frequently in the simulations and facilitated the development of an older age structure.


      The distribution of area among stand conditions within pinyon-juniper woodland fluctuated markedly over time, as expected (Figure-conditions). For example, the percentage of pinyon-juniper woodland in the tree-dominated stage varied from 1% to 44%, reflecting the dynamic nature of this cover type when considered over century-long periods. However, given the scarcity of this cover type in the project area, it was not surprising that the range of variation was so wide. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), and appeared to reach equilibrium relatively quickly compared to other cover types. The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). The herb-dominated condition was particularly dynamic, with coefficients of variation typically two to several times greater than the later seral stages.


      Our estimate of the current seral-stage distribution was infrequently observed under the simulated HRV (Figure-hrv). In particular, the current landscape contains much less area in the shrub-tree stage and much more in the tree-dominated stage than was observed under the simulated HRV, which, in combination with the herb-dominated and herb-shrub stages, resulted in an overall seral-stage departure index of 62% (Table-hrv). The current seral-stage configuration deviated similarly (66%) from the simulated HRV, although the magnitude of departure varied considerably among metrics. In general, the current landscape contains fewer, larger and more clumped (less isolated) patches of the same seral stage than existed under the simulated HRV. WARNING, due to the scarcity of this cover type within the project area and the lack of reliable field data on current stand age and condition in this cover type, these findings must be viewed with extreme caution. Until more complete data are obtained, we are unable to reach firm conclusions regarding HRV departure for this cover type.


Pinyon-Juniper-Sagebrush Woodland [cover type description]


      In general, the vegetation dynamics in pinyon-juniper-sagebrush woodland were very similar to those of pinyon-juniper woodland. Nevertheless, we provide a complete description of the results for this cover type below and highlight the notable differences.


      Pinyon-juniper-sagebrush woodland is three times more common than pinyon-juniper woodland on the SJNF, encompassing 15,992 ha and comprising almost 2% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in pinyon-juniper-sagebrush woodland varied markedly among decades (Figure-initiations, Figure-extent). In most decades, >5% of the pinyon-juniper-sagebrush woodland burned, inclusive of both high- and low-mortality affected areas, and roughly once per 100 years, >20% of the area burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 24 years to >800 years, with a mean and median of 123 and 133 years, respectively, and roughly 2% of the area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return intervals varied spatially across the forest (Figure-map), but given the scarcity of this cover type it was impossible to discern whether there were any meaningful patterns.


      The frequency and extent of simulated pinyon decline epidemics in pinyon-juniper-sagebrush woodland varied among decades in an episodic fashion (Figure-initiations, Figure-extent). In most decades, pinyon decline was at endemic levels and <1% of the pinyon-juniper-sagebrush woodland was disturbed. However, roughly once every 200 years an epidemic affecting >20% of the host area would occur, and roughly once every 300-400 years a major epidemic affecting >40% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 80 years to >800 years, with a mean and median of 337 and 400 years, respectively, although ~9% of the eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest (Figure-map), but given the scarcity of this cover type it was impossible to discern whether there were any meaningful patterns.


      The age structure and dynamics of pinyon-juniper-sagebrush woodland reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the pinyon-juniper-sagebrush woodland was >90 years since stand origin, although at any point in time this varied from 24% to 80% (Figure-survivorship). On average, 25% of the pinyon-juniper-sagebrush woodland survived to >200 years, and <1% survived a stand-replacing disturbance for >800 years. Overall, the age structure of pinyon-juniper-sagebrush woodland was slightly “older” than pinyon-juniper woodland. Note, the relatively “young” age distribution of this cover type (compared to expectations for this cover type) was due to its landscape position in the project area, where it exists as small disjunct patches at the higher range of its elevational distribution and is juxtaposed to ponderosa pine forests and mountain shrublands - which burned frequently in the simulations. Lower elevation, more extensive pinyon-juniper-sagebrush woodlands just outside the project boundary burned less frequently in the simulations and facilitated the development of an older age structure.


      The distribution of area among stand conditions within pinyon-juniper-sagebrush woodland fluctuated markedly over time, as expected (Figure-conditions). For example, the percentage of pinyon-juniper-sagebrush woodland in the tree-dominated stage varied from 1% to 50%, reflecting the dynamic nature of this cover type when considered over century-long periods. However, given the scarcity of this cover type in the project area, it was not surprising that the range of variation was so wide. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), and appeared to reach equilibrium relatively quickly compared to other cover types. The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). The herb-dominated condition was particularly dynamic, with coefficients of variation typically two to several times greater than the later seral stages.


      Our estimate of the current seral-stage distribution was infrequently observed under the simulated HRV (Figure-hrv). In particular, the current landscape contains less area in the shrub-tree stage and more in the tree-dominated stage than was ever observed under the simulated HRV, which, in combination with the herb-dominated and herb-shrub stages, resulted in an overall seral-stage departure index of 50% (Table-hrv). The current seral-stage configuration deviated similarly (62%) from the simulated HRV, although the magnitude of departure varied considerably among metrics. In general, the current landscape contains fewer, larger and more clumped (less isolated) patches of the same seral stage than existed under the simulated HRV. WARNING, due to the scarcity of this cover type within the project area and the lack of reliable field data on current stand age and condition in this cover type, these findings must be viewed with extreme caution. Until more complete data are obtained, we are unable to reach firm conclusions regarding HRV departure for this cover type.


Pinyon-Juniper-Oak-Serviceberry Woodland [cover type description]


      In general, the vegetation dynamics in pinyon-juniper-oak-serviceberry woodland were very similar to those of pinyon-juniper woodland. Nevertheless, we provide a complete description of the results for this cover type below and highlight the notable differences.


      Pinyon-juniper-oak-serviceberry woodland is almost twice as common than pinyon-juniper woodland on the SJNF, encompassing 9,780 ha and comprising roughly 1% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in pinyon-juniper-oak-serviceberry woodland varied markedly among decades (Figure-initiations, Figure-extent). In most decades, >5% of the pinyon-juniper-oak-serviceberry woodland burned, inclusive of both high- and low-mortality affected areas, and roughly once per 100 years, >25% of the area burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 26 years to >800 years, with a mean and median of 108 and 114 years, respectively, and roughly 2% of the area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return intervals varied spatially across the forest (Figure-map), but given the scarcity of this cover type it was impossible to discern whether there were any meaningful patterns.


      The frequency and extent of simulated pinyon decline epidemics in pinyon-juniper-oak-serviceberry woodland varied among decades in an episodic fashion (Figure-initiations, Figure-extent). In most decades, pinyon decline was at endemic levels and <1% of the pinyon-juniper-oak-serviceberry woodland was disturbed. However, roughly once every 200 years an epidemic affecting >15% of the host area would occur, and roughly once every 300-400 years a major epidemic affecting >30% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 80 years to >800 years, with a mean and median of 378 and 400 years, respectively, although ~13% of the eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest (Figure-map), but given the scarcity of this cover type it was impossible to discern whether there were any meaningful patterns.


      The age structure and dynamics of pinyon-juniper-oak-serviceberry woodland reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the pinyon-juniper-oak-serviceberry woodland was >80 years since stand origin, although at any point in time this varied from 17% to 84% (Figure-survivorship). On average, 25% of the pinyon-juniper-oak-serviceberry woodland survived to >170 years, and <1% survived a stand-replacing disturbance for >800 years. Overall, the age structure of pinyon-juniper-oak-serviceberry woodland was intermediate between the slightly “younger” distribution of pinyon-juniper woodland and the slightly “older” distribution of pinyon-juniper-sagebrush woodland. Note, the relatively “young” age distribution of this cover type (compared to expectations for this cover type) was due to its landscape position in the project area, where it exists as small disjunct patches at the higher range of its elevational distribution and is juxtaposed to ponderosa pine forests and mountain shrublands - which burned frequently in the simulations. Lower elevation, more extensive pinyon-juniper-oak-serviceberry woodlands just outside the project boundary burned less frequently in the simulations and facilitated the development of an older age structure.


      The distribution of area among stand conditions within pinyon-juniper-oak-serviceberry woodland fluctuated markedly over time, as expected (Figure-conditions). For example, the percentage of pinyon-juniper-oak-serviceberry woodland in the tree-dominated stage varied from 1% to 49%, reflecting the dynamic nature of this cover type when considered over century-long periods. However, given the scarcity of this cover type in the project area, it was not surprising that the range of variation was so wide. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), and appeared to reach equilibrium relatively quickly compared to other cover types. The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). The herb-dominated condition was particularly dynamic, with coefficients of variation typically two to several times greater than the later seral stages.


      Our estimate of the current seral-stage distribution was infrequently observed under the simulated HRV, but this was mainly due to departure in the tree-dominated stage (Figure-hrv). In particular, the current landscape contains more area in the tree-dominated stage than was often observed under the simulated HRV, which, in combination with the other stand conditions, resulted in an overall seral-stage departure index of only 24% (Table-hrv). The current seral-stage configuration deviated much more dramatically (61%) from the simulated HRV (a departure level consistent with other pinyon-juniper cover types), and the magnitude of departure varied considerably among metrics. In general, the current landscape contains fewer, larger and more clumped (less isolated) patches of the same seral stage than existed under the simulated HRV. WARNING, due to the scarcity of this cover type within the project area and the lack of reliable field data on current stand age and condition in this cover type, these findings must be viewed with extreme caution. Until more complete data are obtained, we are unable to reach firm conclusions regarding HRV departure for this cover type.


Mountian Shrubland [cover type description]


      Mountain shrubland is the second most common cover type on the SJNF, encompassing 118,935 ha and comprising roughly 14% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in mountain shrubland varied markedly among decades (Figure-initiations, Figure-extent). Wildfire was fairly common in this cover type. In most decades, >5% of the mountain shrubland burned, inclusive of both high- and low-mortality affected areas, and roughly 2 times per 100 years, >20% of the area burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 23 years to >800 years, with a mean and median of 73 years, and almost no eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). Interestingly, the return interval distribution was strongly bimodal, suggesting that there was in fact two separate disturbance regimes in this cover type. This largely reflected the bimodal elevation distribution of this cover type (Figure-elevation). Higher-elevation shrubland (3000-4000 m) exhibited a much longer average return interval (~160 years) than lower-elevation shrubland (2000-3000 m; 60 years), reflecting the moister, cooler conditions at higher elevations and the lower frequency of wildfire in general at higher elevations (Figure-map).


      The age structure and dynamics of mountain shrubland reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest individuals in the stand. On average (over time), roughly 50% of the mountain shrubland was >50 years since stand origin, although at any point in time this varied from 25% to 69% (Figure-survivorship). On average, 25% of the mountain shrubland survived to >100 years, and <1% survived a stand-replacing disturbance for >400 years.


      The distribution of area among stand conditions within mountain shrubland fluctuated over time, as expected (Figure-conditions). For example, the percentage of mountain shrubland in the late shrub-dominated stage varied from 25% to 69%, reflecting the dynamic nature of this cover type when considered over century-long periods. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), and appeared to reach equilibrium relatively quickly compared to other cover types. The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area and the proximity index (a measure of patch isolation) exhibited the greatest variability and the herb-shrub condition was particularly dynamic relative to the early and late shrub-dominated stages.


      Our estimate of the current seral-stage distribution was almost never observed under the simulated HRV (Figure-hrv). In particular, the current landscape contains more area in the herb-shrub and early shrub-dominated stage and less in the late shrub-dominated stage than was observed under the simulated HRV, which resulted in an overall seral-stage departure index of 97% (Table-hrv). The current seral-stage configuration deviated much less dramatically but still substantially (71%) from the simulated HRV. The magnitude of departure varied dramatically among metrics. In general, the current landscape contains fewer, larger and more geometrically complex and clumped (less isolated) patches of the same seral stage than existed under the simulated HRV, although the nature and magnitude of departure differed considerably among stand conditions. WARNING, due to the lack of reliable field data on current stand age and condition in this cover type, these findings must be viewed with extreme caution. Until more complete data are obtained, we are unable to reach firm conclusions regarding HRV departure for this cover type.


Ponderosa Pine-Oak Forest [cover type description]


      Ponderosa pine-oak forest is a fairly common cover type on the SJNF, encompassing 67,933 ha and comprising roughly 8% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in ponderosa pine-oak forest varied markedly among decades (Figure-initiations, Figure-extent). Wildfire was quite prevalent in this cover type. In most decades, >10% of the ponderosa pine-oak forest burned, inclusive of both high- and low-mortality affected areas, and roughly 3-4 times per 100 years, >30% of the area burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 19 years to >800 years, with a mean and median of 38 years, and almost no eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). Note, the return interval between low-mortality fires as measured by the sample-based approach (in which each recorded interval between low-mortality fires in a cell was treated as an independent observation, in order to approximate the method of most dendrochronological fire history studies) was somewhat shorter (30 years; Figure-return). As expected, return intervals varied spatially across the forest (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. In addition, ponderosa pine-oak stands embedded in a neighborhood containing cover types with longer return intervals (e.g., aspen, cool moist mixed-conifer forest) exhibited longer return intervals, reflecting the importance of landscape context on fire regimes.


      The frequency and extent of simulated pine beetle epidemics in ponderosa pine-oak forest varied markedly among decades (Figure-initiations, Figure-extent). In most decades, pine beetles were at endemic levels and none of the ponderosa pine-oak forest was disturbed. However, 1-3 times per 100 years an epidemic occurred. On average, once every 70 years an epidemic affecting >10% of the host area would occur, and roughly once every 300 years a major epidemic affecting >20% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 50 years to >800 years, with a mean and median of 251 and 267 years, respectively, although ~5% of the eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The age structure and dynamics of ponderosa pine-oak forest reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the ponderosa pine-oak forest was >380 years since stand origin, although at any point in time this varied from 2% to 66% (Figure-survivorship). On average, 25% of the ponderosa pine-oak forest survived to >580 years, and roughly 8% survived a stand-replacing disturbance for >800 years. The relatively “old” age structure of this cover type may seem surprising at first; however, most wildfires in this cover type were low-mortality fires that did not result in stand reinitiation.


      The distribution of area among stand conditions within ponderosa pine-oak forest fluctuated over time, as expected (Figure-conditions). For example, the percentage of ponderosa pine-oak forest in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions) varied from 8% to 42%, reflecting the dynamic nature of this cover type when considered over century-long periods. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), and appeared to reach equilibrium relatively quickly compared to other cover types. The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area and extent (radius of gyration) and the proximity index (a measure of patch isolation) exhibited the greatest variability and the understory reinitiation condition was particularly dynamic relative to the earlier and later stages.


      Our estimate of the current seral-stage distribution was never observed under the simulated HRV (Figure-hrv). The most notable departure was in the fire-maintained open canopy (FMO) condition. The current landscape contains no ponderosa pine-oak forest in the FMO condition, yet this condition was always well represented (39-77%) under the simulated HRV. Similarly, the current landscape contains 67% of the cover type in the stem exclusion condition, yet this large a percentage was never observed under the simulated HRV (range 7-14%). The stand initiation condition and late-seral stages combined were both within their 25-75th percentile ranges of variation under simulated HRV. Overall, based on the five separate stand conditions (i.e., without aggregating the late-seral stages), the seral-stage departure index was 80% (Table-hrv). When the late-seral stages were aggregated, the seral-stage departure index declined dramatically to 50%. The current seral-stage configuration deviated more dramatically (94%) from the simulated HRV and was relatively consistent among metrics, with the lowest departure index equal to 80%. Despite the difficulties in classifying the late-seral stages in the current landscape, there is consistent evidence that, in general, the current landscape contains fewer, larger and more geometrically complex and clumped (less isolated) patches of all seral stages than existed under the simulated HRV.


Ponderosa Pine-Oak-Aspen Forest [cover type description]


      In general, the vegetation dynamics in ponderosa pine-oak-aspen forest were very similar to those of ponderosa pine-oak forest. Nevertheless, we provide a complete description of the results for this cover type below and highlight the notable differences.


      Ponderosa pine-oak-aspen forest is roughly half as common as ponderosa pine-oak forest on the SJNF, encompassing 35,823 ha and comprising roughly 4% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in ponderosa pine-oak-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). Wildfire was quite prevalent in this cover type, but somewhat less so than in ponderosa pine-oak forest. In most decades, >10% of the ponderosa pine-oak-aspen forest burned, inclusive of both high- and low-mortality affected areas, and roughly 2-3 times per 100 years, >30% of the area burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 21 years to >800 years, with a mean and median of 46 years, and almost no eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). Note, the return interval between low-mortality fires as measured by the sample-based approach (in which each recorded interval between low-mortality fires in a cell was treated as an independent observation, in order to approximate the method of most dendrochronological fire history studies) was somewhat shorter (43 years; Figure-return). As expected, return intervals varied spatially across the forest (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. In addition, ponderosa pine-oak-aspen stands embedded in a neighborhood containing cover types with longer return intervals (e.g., aspen, cool moist mixed-conifer forest) exhibited longer return intervals, reflecting the importance of landscape context on fire regimes. The wildfire return interval was roughly eight years longer than observed for ponderosa pine-oak forest, reflecting the slightly higher elevation of this cover type (and hence cooler, moister conditions) and the reduced flammability (and hence wildfire susceptibility) of the aspen component in this cover type.


      The frequency and extent of simulated pine beetle epidemics in ponderosa pine-oak-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). In most decades, pine beetles were at endemic levels and none of the ponderosa pine-oak-aspen forest was disturbed. However, 1-3 times per 100 years an epidemic occurred. On average, once every 70 years an epidemic affecting >10% of the host area would occur, and roughly once every 300 years a major epidemic affecting >20% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 50 years to >800 years, with a mean and median of 230 and 267 years, respectively, although ~5% of the eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The age structure and dynamics of ponderosa pine-oak-aspen forest reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the ponderosa pine-oak-aspen forest was >390 years since stand origin, although at any point in time this varied from <1% to >71% (Figure-survivorship). On average, 25% of the ponderosa pine-oak-aspen forest survived to >590 years, and roughly 8% survived a stand-replacing disturbance for >800 years. The relatively “old” age structure of this cover type may seem surprising at first; however, most wildfires in this cover type were low-mortality fires that did not result in stand reinitiation.


      The distribution of area among stand conditions within ponderosa pine-oak-aspen forest fluctuated over time, as expected (Figure-conditions). For example, the percentage of ponderosa pine-oak-aspen forest in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions) varied from 15% to 50% (slightly greater values than in ponderosa pine-oak forest), reflecting the dynamic nature of this cover type when considered over century-long periods. However, the fluctuations in the seral-stage distribution were much less pronounced in this cover than in most others. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean). The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area and extent (radius of gyration) and the proximity index (a measure of patch isolation) exhibited the greatest variability and the understory reinitiation condition was particularly dynamic relative to the earlier and later stages.


      Our estimate of the current seral-stage distribution was never observed under the simulated HRV (Figure-hrv). As with ponderosa pine-oak forest, the most notable departure was in the fire-maintained open canopy (FMO) condition. The current landscape contains no ponderosa pine-oak-aspen forest in the FMO condition, yet this condition was always well represented (40-76%) under the simulated HRV. Similarly, the current landscape contains 88% of the cover type in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions), yet this high a percentage was never observed under the simulated HRV. There was a notable difference in departure between ponderosa pine-oak forest with and without aspen. The current landscape contains much less ponderosa pine with aspen in the stem exclusion stage than in the pure ponderosa pine cover type (11% versus 67%). This is likely due to differences between cover types in the rate of succession from the stem exclusion stage to the understory reinitiation stage. In the ponderosa pine with aspen type, the stem exclusion stage is dominated by aspen, which transitions to the understory reinitiation stage between 80-120 years after stand origin - owing to the relatively short-lived aspen and early break-up of the aspen-dominated canopy. In contrast, the conifer canopy in the pure ponderosa pine forest takes 150-250 years to break up in the absence of other major disturbance processes. Hence, in the absence of wildfires over the past century, most ponderosa pine-oak-aspen stands have already transitioned to the understory reinitiation stage, whereas a larger proportion of the pure ponderosa pine stands have not yet transitioned. Overall, based on the five separate stand conditions (i.e., without aggregating the late-seral stages), the seral-stage departure index for ponderosa pine-oak-aspen was 91% (Table-hrv), which is 11% greater than observed for ponderosa pine-oak forest. When the late-seral stages were aggregated, the seral-stage departure index declined slightly to 89%. The current seral-stage configuration deviated even more dramatically (94%) from the simulated HRV and was relatively consistent among metrics, with the lowest departure index equal to 75%. Despite the difficulties in classifying the late-seral stages in the current landscape, there is consistent evidence that, in general, the current landscape contains fewer, larger and more geometrically complex and clumped (less isolated) patches of all seral stages than existed under the simulated HRV.


Warm-Dry Mixed-Conifer Forest [cover type description]


      Warm dry mixed-conifer forest is a somewhat common cover type on the SJNF, encompassing 49,237 ha and comprising roughly 6% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in warm dry mixed-conifer forest varied markedly among decades (Figure-initiations, Figure-extent). Wildfire was quite prevalent in this cover type. In most decades, >10% of the warm dry mixed-conifer forest burned, inclusive of both high- and low-mortality affected areas, and roughly 1-2 times per 100 years, >30% of the area burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 24 years to >800 years, with a mean and median of 53 and 50 years, respectively, and almost no eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return intervals varied spatially across the forest (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. In addition, warm dry mixed-conifer stands embedded in a neighborhood containing cover types with longer return intervals (e.g., aspen, cool moist mixed-conifer forest) exhibited longer return intervals, reflecting the importance of landscape context on fire regimes.


      Spruce beetles can venture into warm dry mixed-conifer forest, but due to the scarce and patchy distribution of suitable host trees in this cover type, epidemics are relatively insignificant and have negligible impact on this cover type (Figure-initiations, Figure-extent). Only occasionally (e.g., once every 400-800 years) did spruce beetles disturb >1% of the warm dry mixed-conifer forest, inclusive of both high- and low-mortality affected areas (Figure-recurrence). Consequently, return intervals between epidemics (of any mortality level) at a single location typically exceeded 800 years (Figure-return).


      The frequency and extent of simulated spruce budworm epidemics in warm dry mixed-conifer forest varied markedly among decades (Figure-initiations, Figure-extent). In almost two-thirds of the decades, spruce budworm populations were at endemic levels and none of the warm dry mixed-conifer forest was disturbed. However, 2-3 times per 100 years, epidemics occurred affecting >10% of the area, inclusive of both high- and low-mortality affected areas, and approximately once every 200 years, >40% of the warm dry mixed-conifer forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied from 36 years to >800 years, with a mean and median of 130 and 133 years, respectively, although very little eligible area (~1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The frequency and extent of simulated Douglas-fir beetle epidemics in warm dry mixed-conifer forest varied markedly among decades (Figure-initiations, Figure-extent). In most decades <1% of the warm dry mixed-conifer forest area was affected by an outbreak; however, 2-3 times per 100 years an epidemic affecting >2% of the host area would occur, and once every 300 years an epidemic would affect >6% of the host area (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 89 years to >800 years, with a mean and median of 695 and 800 years, respectively, although a large portion of the area (>30%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The frequency and extent of simulated pine beetle epidemics in warm dry mixed-conifer forest varied markedly among decades (Figure-initiations, Figure-extent). In most decades, pine beetles were at endemic levels and none of the warm dry mixed-conifer forest was disturbed. However, 1-3 times per 100 years an epidemic occurred. On average, once every 50 years an epidemic affecting >5% of the host area would occur, and roughly once every 400 years a major epidemic affecting >20% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 67 years to >800 years, with a mean and median of 395 and 400 years, respectively, although >10% of the eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The age structure and dynamics of warm dry mixed-conifer forest reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the warm dry mixed-conifer forest was >350 years since stand origin, although at any point in time this varied from <9% to >61% (Figure-survivorship). On average, 25% of the warm dry mixed-conifer forest survived to >550 years, and roughly 8% survived a stand-replacing disturbance for >800 years. The relatively “old” age structure of this cover type may seem surprising at first; however, most wildfires in this cover type were low-mortality fires that did not result in stand reinitiation.


      The distribution of area among stand conditions within warm dry mixed-conifer forest fluctuated over time, as expected (Figure-conditions). For example, the percentage of warm dry mixed-conifer forest in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions) varied from 21% to 57%, reflecting the dynamic nature of this cover type when considered over century-long periods. However, the fluctuations in the seral-stage distribution were much less pronounced in this cover type than in most others, with the exception of the ponderosa pine forest types. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), and appeared to reach equilibrium relatively quickly compared to other cover types. The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area and extent (radius of gyration) and the proximity index (a measure of patch isolation) exhibited the greatest variability and the stand initiation and understory reinitiation conditions were particularly dynamic relative to the other stages.


      Our estimate of the current seral-stage distribution was never observed under the simulated HRV (Figure-hrv). The most notable departure was in the fire-maintained open canopy (FMO) condition. The current landscape contains no warm dry mixed-conifer forest in the FMO condition, yet this condition was always well represented (28-64%) under the simulated HRV. Similarly, the current landscape contains 27% of the cover type in the stem exclusion condition and 69% in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions), yet these high percentages were never observed under the simulated HRV. The only stand condition not deviating from the simulated HRV was the stand initiation condition. Overall, based on the five separate stand conditions (i.e., without aggregating the late-seral stages), the seral-stage departure index was 80% (Table-hrv). When the late-seral stages were aggregated, the seral-stage departure index declined slightly to 75%. The current seral-stage configuration deviated more dramatically (94%) from the simulated HRV and was relatively consistent among metrics, with the lowest departure index equal to 73%. Despite the difficulties in classifying the late-seral stages in the current landscape, there is consistent evidence that, in general, the current landscape contains fewer, larger and more geometrically complex and clumped (less isolated) patches of all seral stages than existed under the simulated HRV.


Warm-Dry Mixed-Conifer with Aspen Forest [cover type description]


      In general, the vegetation dynamics in warm dry mixed-conifer-aspen forest were very similar to those of warm dry moist mixed-conifer forest. Nevertheless, we provide a complete description of the results for this cover type below and highlight the notable differences.


      Warm dry mixed-conifer-aspen forest is just as common as warm dry mixed-conifer forest on the SJNF, encompassing 48,204 ha and comprising roughly 6% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in warm dry mixed-conifer-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). Wildfire was quite prevalent in this cover type. In most decades, >10% of the warm dry mixed-conifer-aspen forest burned, inclusive of both high- and low-mortality affected areas, and roughly once per 100 years, >30% of the area burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 25 years to >800 years, with a mean and median of 62 years, and almost no eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return intervals varied spatially across the forest (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. In addition, warm dry mixed-conifer-aspen stands embedded in a neighborhood containing cover types with longer return intervals (e.g., aspen, cool moist mixed-conifer forest) exhibited longer return intervals, reflecting the importance of landscape context on fire regimes. The wildfire return interval was roughly 10 years longer than observed for warm dry mixed-conifer forest, reflecting the slightly higher elevation of this cover type (and hence cooler, moister conditions) and the reduced flammability (and hence wildfire susceptibility) of the aspen component in this cover type.


      Spruce beetles can venture into warm dry mixed-conifer-aspen forest, but due to the scarce and patchy distribution of suitable host trees in this cover type, epidemics are relatively insignificant and have negligible impact on this cover type (Figure-initiations, Figure-extent). Only occasionally (e.g., once every 400-800 years) did spruce beetles disturb >1% of the warm dry mixed-conifer-aspen forest, inclusive of both high- and low-mortality affected areas (Figure-recurrence). Consequently, return intervals between epidemics (of any mortality level) at a single location typically exceeded 800 years (Figure-return).


      The frequency and extent of simulated spruce budworm epidemics in warm dry mixed-conifer-aspen forest varied markedly among decades (Figure-initiations, Figure-extent), and were slightly less prevalent than in warm dry mixed-conifer forest due to the lower density of suitable host trees. In almost two-thirds of the decades, spruce budworm populations were at endemic levels and none of the warm dry mixed-conifer-aspen forest was disturbed. However, 2-3 times per 100 years, epidemics occurred affecting >10% of the area, inclusive of both high- and low-mortality affected areas, and approximately once every 200 years, >30% of the warm dry mixed-conifer-aspen forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied from 36 years to >800 years, with a mean and median of 136 and 133 years, respectively, although very little eligible area (~2%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The frequency and extent of simulated Douglas-fir beetle epidemics in warm dry mixed-conifer-aspen forest varied markedly among decades (Figure-initiations, Figure-extent), and were slightly less prevalent than in warm dry mixed-conifer forest due to the lower density of suitable host trees. In most decades <1% of the warm dry mixed-conifer-aspen forest area was affected by an outbreak; however, 2-3 times per 100 years an epidemic affecting >2% of the host area would occur, and once every 300-400 years an epidemic would affect >6% (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 80 years to >800 years, with a mean and median of 751 and 800 years, respectively, although a large portion of the area (>35%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The frequency and extent of simulated pine beetle epidemics in warm dry mixed-conifer-aspen forest varied markedly among decades (Figure-initiations, Figure-extent), and were slightly less prevalent than in warm dry mixed-conifer forest due to the lower density of suitable host trees. In most decades, pine beetles were at endemic levels and none of the warm dry mixed-conifer-aspen forest was disturbed. However, 1-3 times per 100 years an epidemic occurred. On average, once every 50 years an epidemic affecting >5% of the host area would occur, and roughly once every 400 years a major epidemic affecting >15% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 62 years to >800 years, with a mean and median of 425 and 400 years, respectively, although >15% of the eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The age structure and dynamics of warm dry mixed-conifer-aspen forest reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the warm dry mixed-conifer-aspen forest was >350 years since stand origin, although at any point in time this varied from <8% to >63% (Figure-survivorship). On average, 25% of the warm dry mixed-conifer-aspen forest survived to >550 years, and roughly 8% survived a stand-replacing disturbance for >800 years. The relatively “old” age structure of this cover type may seem surprising at first; however, most wildfires in this cover type were low-mortality fires that did not result in stand reinitiation.


      The distribution of area among stand conditions within warm dry mixed-conifer-aspen forest fluctuated over time, as expected (Figure-conditions). For example, the percentage of warm dry mixed-conifer-aspen forest in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions) varied from 27% to 62% (slightly greater values than in warm dry mixed-conifer forest), reflecting the dynamic nature of this cover type when considered over century-long periods. However, the fluctuations in the seral-stage distribution were much less pronounced in this cover type than in most others, with the exception of the ponderosa pine forest types. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean). The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area and extent (radius of gyration) and the proximity index (a measure of patch isolation) exhibited the greatest variability and the understory reinitiation condition was particularly dynamic relative to the other stages.


      Our estimate of the current seral-stage distribution was never observed under the simulated HRV (Figure-hrv). As with warm dry mixed-conifer forest, the most notable departure was in the fire-maintained open canopy (FMO) condition. The current landscape contains no warm dry mixed-conifer-aspen forest in the FMO condition, yet this condition was always well represented (24-57%) under the simulated HRV. Similarly, the current landscape contains 89% of the cover type in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions), yet this high a percentage was never observed under the simulated HRV. There was a notable difference in seral-stage departure between warm dry mixed-conifer forest with and without aspen. The current landscape contains much less mixed-conifer with aspen in the stem exclusion stage than in the pure conifer cover type (7% versus 27%). This is likely due to differences between cover types in the rate of succession from the stem exclusion stage to the understory reinitiation stage. In the mixed-conifer with aspen type, the stem exclusion stage is dominated by aspen, which transitions to the understory reinitiation stage between 80-120 years after stand origin - owing to the relatively short-lived aspen and early break-up of the aspen-dominated canopy. In contrast, the conifer canopy in the pure conifer forest takes 150-250 years to break up in the absence of other major disturbance processes. Hence, in the absence of wildfires over the past century, most mixed-conifer-aspen stands have already transitioned to the understory reinitiation stage, whereas a larger proportion of the pure conifer stands have not yet transitioned. The only stand condition not deviating from the simulated HRV was the stand initiation condition. Overall, based on the five separate stand conditions (i.e., without aggregating the late-seral stages), the seral-stage departure index was 77% (Table-hrv) - slightly less than observed for warm dry mixed-conifer forest. When the late-seral stages were aggregated, the seral-stage departure index declined slightly to 71%. The current seral-stage configuration deviated much more dramatically (96%) from the simulated HRV and was relatively consistent among metrics, with the lowest departure index equal to 66%. Despite the difficulties in classifying the late-seral stages in the current landscape, there is consistent evidence that, in general, the current landscape contains fewer, larger and more geometrically complex and clumped (less isolated) patches of all seral stages than existed under the simulated HRV.


Cool-Moist Mixed-Conifer Forest [cover type description]


      Cool moist mixed-conifer forest is a somewhat common cover type on the SJNF, encompassing 34,287 ha and comprising roughly 4% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in cool moist mixed-conifer forest varied markedly among decades (Figure-initiations, Figure-extent). In about one third of the decades, less than 1% of the cool moist mixed-conifer forest burned, inclusive of both high- and low-mortality affected areas. However, on average, 2-3 times per 100 years, >10% of the area burned, and roughly once every 150-200 years, >20% of the cool moist mixed-conifer forest burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 26 years to >800 years, with a mean and median of 144 and 160 years, respectively, although very little eligible area (<1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return intervals varied spatially across the forest (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. In addition, cool moist mixed-conifer stands embedded in a neighborhood containing cover types with shorter return intervals (e.g., aspen, mountain shrubland) exhibited shorter return intervals, reflecting the importance of landscape context on fire regimes.


      The frequency and extent of simulated spruce beetle epidemics in cool moist mixed-conifer forest varied markedly among decades (Figure-initiations, Figure-extent). In about one third of the decades, less than 1% of the cool moist mixed-conifer forest was disturbed, inclusive of both high- and low-mortality affected areas. However, on average, roughly once per 100 years, >10% of the area was disturbed, and at least once every 400 years, >20% of the cool moist mixed-conifer forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied widely from 53 years to >800 years, with a mean and median of 370 and 400 years, respectively, although >20% of the eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). Not surprisingly, the return interval varied spatially across the forest and exhibited a somewhat contagious or clumped distribution (Figure-map). In general, areas of extensive and connected cool moist mixed-conifer forest at the highest elevations where it is juxtaposed to spruce-fir forest (the most susceptible cover type) exhibited the shortest return intervals, but there was considerable variation among runs owing to the stochastic nature of spruce beetle outbreaks.


      The frequency and extent of simulated spruce budworm epidemics in cool moist mixed-conifer forest varied markedly among decades (Figure-initiations, Figure-extent). In almost two-thirds of the decades, spruce budworm populations were at endemic levels and none of the cool moist mixed-conifer forest was disturbed. However, roughly 3 times per 100 years, epidemics occurred affecting >10% of the area, inclusive of both high- and low-mortality affected areas, and approximately once every 150 years, >50% of the cool moist mixed-conifer forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied from 33 years to >800 years, with a mean and median of roughly 90 years, although almost no eligible area (<1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The frequency and extent of simulated Douglas-fir beetle epidemics in cool moist mixed-conifer forest varied markedly among decades (Figure-initiations, Figure-extent). In most decades <1% of the cool moist mixed-conifer forest area was affected by an outbreak; however, at least once every 400 years an epidemic affecting >2% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 114 years to >800 years, with a mean and median of >800 years; in fact most of the area (>70%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The age structure and dynamics of cool moist mixed-conifer forest reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the cool moist mixed-conifer forest was >150 years since stand origin, although at any point in time this varied from <33% to >70% (Figure-survivorship). On average, 28% of the cool moist mixed-conifer forest survived to >300 years, 5% survived to >590 years, and a very small percentage (<1%) survived a stand-replacing disturbance for >800 years. This highlights the stochastic nature of disturbances, in which some areas by chance alone escaped catastrophic disturbance for very long periods.


      The distribution of area among stand conditions within cool moist mixed-conifer forest fluctuated over time, as expected (Figure-conditions). For example, the percentage of cool moist mixed-conifer forest in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions) varied from 38% to 73%, reflecting the extremely dynamic nature of this high-elevation forest cover type when considered over century-long periods. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), despite the fact that the proportion in each condition during any snapshot (i.e., time step) varied considerably over time. The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area, core area and the proximity index (a measure of patch isolation) exhibited the greatest variability over time.


      Our estimate of the current seral-stage distribution was never observed under the simulated HRV (Figure-hrv). The most notable departure was in the early (i.e., stand initiation) and late-seral stages (i.e., understory reinitiation and shifting mosaic conditions). The current landscape contains only 2% of the cool moist mixed-conifer forest in the stand initiation condition, yet this condition was always better represented (3-36%) under the simulated HRV. Conversely, the current landscape contains 72% of the cover type in the late-seral stages, yet this high a percentage was the upper extreme of the range observed under the simulated HRV. The current landscape does, however, contain a pulse (26%) of cool moist mixed-conifer forest in the stem exclusion stage, which is well within the simulated HRV (15th percentile of the HRV distribution), perhaps representing a legacy of naturally occurring wildfires during the 19th century. Overall, based on the four separate stand conditions (i.e., without aggregating the late-seral stages), the seral-stage departure index was 85% (Table-hrv). When the late-seral stages were aggregated, the seral-stage departure index declined slightly to 80%. The current seral-stage configuration deviated similarly (87%) from the simulated HRV and was relatively consistent among metrics, with the lowest departure index equal to 68%. Unfortunately, the nature of the configuration departure varied depending on whether the late-seral stages were treated separately or combined into a single class. Thus, the only reliable conclusion we can reach is that, in general, the current landscape contains fewer, smaller and geometrically less complex and more isolated patches of early-seral forest than existed under the simulated HRV.


Cool-Moist Mixed-Conifer with Aspen Forest [cover type description]


      In general, the vegetation dynamics in cool moist mixed-conifer-aspen forest were very similar to those of cool moist mixed-conifer forest. Nevertheless, we provide a complete description of the results for this cover type below and highlight the notable differences.


      Cool moist mixed-conifer-aspen forest is twice as common as cool moist mixed-conifer forest on the SJNF, encompassing 78,407 ha and comprising roughly 9% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in cool moist mixed-conifer-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). In about one third of the decades, less than 1% of the cool moist mixed-conifer-aspen forest burned, inclusive of both high- and low-mortality affected areas. However, on average, 2-3 times per 100 years, >10% of the area burned, and roughly once every 150-200 years, >20% of the cool moist mixed-conifer-aspen forest burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 29 years to >800 years, with a mean and median of 136 and 160 years, respectively, although very little eligible area (<1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return intervals varied spatially across the forest (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. In addition, cool moist mixed-conifer-aspen stands embedded in a neighborhood containing cover types with shorter return intervals (e.g., aspen, mountain shrubland) exhibited shorter return intervals, reflecting the importance of landscape context on fire regimes.


      The frequency and extent of simulated spruce beetle epidemics in cool moist mixed-conifer-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). In almost half the decades, less than 1% of the cool moist mixed-conifer-aspen forest was disturbed, inclusive of both high- and low-mortality affected areas. However, on average, roughly once per 100 years, >10% of the area was disturbed, and at least once every 400 years, >20% of the cool moist mixed-conifer-aspen forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied widely from 62 years to >800 years, with a mean and median of 392 and 400 years, respectively, although >20% of the eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). Not surprisingly, the return interval varied spatially across the forest and exhibited a decidedly contagious or clumped distribution (Figure-map). In general, areas of extensive and connected cool moist mixed-conifer-aspen forest at the highest elevations where it is juxtaposed to spruce-fir forest (the most susceptible cover type) exhibited the shortest return intervals, but there was considerable variation among runs owing to the stochastic nature of spruce beetle outbreaks.


      The frequency and extent of simulated spruce budworm epidemics in cool moist mixed-conifer-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). In almost two-thirds of the decades, spruce budworm populations were at endemic levels and none of the cool moist mixed-conifer-aspen forest was disturbed. However, roughly 3 times per 100 years, epidemics occurred affecting >10% of the area, inclusive of both high- and low-mortality affected areas, and approximately once every 150 years, >50% of the cool moist mixed-conifer-aspen forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied from 33 years to >800 years, with a mean and median of 84 and 80 years, respectively, although almost no eligible area (<1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The frequency and extent of simulated Douglas-fir beetle epidemics in cool moist mixed-conifer-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). In most decades <1% of the cool moist mixed-conifer-aspen forest area was affected by an outbreak; however, roughly once every 400 years an epidemic affecting >2% of the host area would occur (Figure-recurrence), inclusive of both high- and low-mortality affected areas. The return interval between epidemics (of any mortality level) at a single location varied from 133 years to >800 years, with a mean and median of >800 years; in fact most of the area (>70%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The age structure and dynamics of cool moist mixed-conifer-aspen forest reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the cool moist mixed-conifer-aspen forest was >140 years since stand origin, although at any point in time this varied from <32% to >69% (Figure-survivorship). On average, 23% of the cool moist mixed-conifer-aspen forest survived to >300 years, 5% survived to >530 years, and a very small percentage (<1%) survived a stand-replacing disturbance for >800 years. This highlights the stochastic nature of disturbances, in which some areas by chance alone escaped catastrophic disturbance for very long periods.


      The distribution of area among stand conditions within cool moist mixed-conifer-aspen forest fluctuated over time, as expected (Figure-conditions). For example, the percentage of cool moist mixed-conifer-aspen forest in late-seral stages (i.e., understory reinitiation and shifting mosaic conditions) varied from 47% to 85%, reflecting the extremely dynamic nature of this high elevation forest cover type when considered over century-long periods. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), despite the fact that the proportion in each condition during any snapshot (i.e., time step) varied considerably over time. For unknown reasons, the equilibration period was somewhat longer for cool moist mixed-conifer-aspen forest than most other cover types (~200 years, instead of ~100 years). The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area, core area and the proximity index (a measure of patch isolation) exhibited the greatest variability over time, and the stand initiation and shifting mosaic stages were particularly dynamic relative to the other stages.


      Our estimate of the current seral-stage distribution was never observed under the simulated HRV (Figure-hrv). The most notable departure was in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions). Specifically, the current landscape contains 88% of this cover type in the late-seral stages, yet this situation was never observed under the simulated HRV. In addition, the current landscape contains only 4% of this cover type in the stand initiation condition, an uncommon situation under the simulated HRV (9th percentile of the HRV distribution), and 8% in the stem exclusion condition, a situation almost never observed under the simulated HRV. Notably, the current landscape contains much less of this cover type in the early- and mid-seral stages (i.e., stand initiation and stem exclusion conditions) than in cool moist mixed-conifer forest (12% versus 28%). This is likely due to differences between cover types in the rate of succession from the stem exclusion stage to the understory reinitiation stage. In the mixed-conifer-aspen forest, the stem exclusion stage is dominated by aspen, which transitions to the understory reinitiation stage between 80-120 years after stand origin - owing to the relatively short-lived aspen and early break-up of the aspen-dominated canopy. In contrast, the conifer canopy in the pure conifer forest takes 150-250 years to break up in the absence of other major disturbance processes. Hence, in the absence of large wildfires over the past century, most mixed-conifer-aspen stands have already transitioned to the understory reinitiation stage, whereas a larger proportion of the pure conifer stands have not yet transitioned. Overall, based on the four separate stand conditions (i.e., without aggregating the late-seral stages), the seral-stage departure index was 91% (Table-hrv) - slightly greater than observed for cool moist mixed-conifer forest. When the late-seral stages were aggregated, the seral-stage departure index declined slightly to 89%. The current seral-stage configuration deviated much less (66%) from the simulated HRV (and considerably less than observed for cool moist mixed-conifer forest), although there was considerable variability (19-99%) among metrics. Unfortunately, the nature of the configuration departure varied depending on whether the late-seral stages were treated separately or combined into a single class. Thus, the only reliable conclusion we can reach is that, in general, the current landscape contains fewer, smaller and geometrically less complex patches of early-seral forest than existed under the simulated HRV.


Pure Aspen Forest [cover type description]


      Pure aspen forest is relatively uncommon on the SJNF, encompassing 21,480 ha and comprising roughly 2.5% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in aspen forest varied markedly among decades (Figure-initiations, Figure-extent). In almost half of the decades, less than 5% of the aspen forest burned, inclusive of both high- and low-mortality affected areas. However, on average, roughly 2-3 times per 100 years, >10% of the area burned, and roughly once every 200 years, >30% of the pure aspen forest burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 26 years to >800 years, with a mean and median of 110 years and 114 years, respectively, and no eligible area escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return interval varied spatially across the forest (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. In addition, pure aspen stands embedded in a neighborhood containing cover types with shorter return intervals (e.g., mountain shrubland) exhibited shorter return intervals, reflecting the importance of landscape context on fire regimes.


      The age structure and dynamics of pure aspen forest reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the pure aspen forest was >90 years since stand origin, although at any point in time this varied from <27% to >80% (Figure-survivorship). On average, 10% of the pure aspen forest survived to >300 years, 5% survived to >360 years, and a very small percentage (<1%) survived a stand-replacing disturbance for >530 years. This highlights the stochastic nature of disturbances, in which some areas by chance alone escaped catastrophic disturbance for very long periods.


      The distribution of area among stand conditions within pure aspen forest fluctuated markedly over time, as expected (Figure-conditions). For example, the percentage of pure aspen forest in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions) varied from 35% to 86%, reflecting the extremely dynamic nature of this cover type when considered over century-long periods. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), despite the fact that the proportion in each condition during any snapshot (i.e., time step) varied considerably over time. The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area, core area and the proximity index (a measure of patch isolation) exhibited the greatest variability over time.


      Our estimate of the current seral-stage distribution was never observed under the simulated HRV (Figure-hrv). Specifically, the current landscape contains <1% of this cover type in the stand initiation condition, a situation never observed under the simulated HRV, and 82% in the late-seral stages (i.e., understory reinitiation and shifting mosaic conditions), a situation almost never observed under the simulated HRV. The current landscape does, however, contain a pulse (17%) of pure aspen forest in the stem exclusion stage, which is well within the simulated HRV (46th percentile of the HRV distribution). Overall, based on the four separate stand conditions (i.e., without aggregating the late-seral stages), the seral-stage departure index was 67% (Table-hrv). When the late-seral stages were aggregated, the seral-stage departure index declined slightly to 65%. The current seral-stage configuration deviated similarly (60%) from the simulated HRV, although there was considerable variability (16-100%) among metrics. In general, the current landscape contains fewer, larger and more clumped (less isolated) late-seral patches and fewer, smaller and geometrically less complex and less clumped (more isolated) early-seral patches of pure aspen forest than existed under the simulated HRV.


Spruce-Fir Forest [cover type description]


      Spruce-fir forest is the predominant cover type on the SJNF, encompassing 153,982 ha and comprising roughly 18% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in spruce-fir forest varied markedly among decades (Figure-initiations, Figure-extent). In almost half of the decades, less than 1% of the spruce-fir forest burned, inclusive of both high- and low-mortality affected areas. However, on average, almost once per 100 years, >10% of the area burned, and roughly once every 300-400 years, >20% of the spruce-fir forest burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 42 years to >800 years, with a mean and median of 267 years, although very little eligible area (1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return intervals varied spatially across the forest (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. In addition, spruce-fir stands embedded in a neighborhood containing cover types with shorter return intervals (e.g., aspen, mountain shrubland) exhibited shorter return intervals, reflecting the importance of landscape context on fire regimes.


      The frequency and extent of simulated spruce beetle epidemics in spruce-fir forest varied markedly among decades (Figure-initiations, Figure-extent). In almost half of the decades, less than 1% of the spruce-fir forest was disturbed, inclusive of both high- and low-mortality affected areas. However, on average, roughly twice per 100 years, >10% of the area was disturbed, and perhaps once every 400 years, >40% of the spruce-fir forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied widely from 47 years to >800 years, with a mean and median of 160 years, although almost no eligible area (<1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). Not surprisingly, the return interval varied spatially across the forest and exhibited a highly contagious or clumped distribution (Figure-map). In general, the areas of most extensive and connected spruce-fir forest exhibited the shortest return intervals, but there was considerable variation among runs owing to the stochastic nature of spruce beetle outbreaks.


      The frequency and extent of simulated spruce budworm epidemics in spruce-fir forest varied markedly among decades (Figure-initiations, Figure-extent). In almost two-thirds of the decades, spruce budworm populations were at endemic levels and none of the spruce-fir forest was disturbed. However, roughly 3 times per 100 years, epidemics occurred affecting >10% of the area, and approximately once every 400 years, 50% of the spruce-fir forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied from 36 years to >800 years, with a mean and median of 114 years, although almost no eligible area (<1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The age structure and dynamics of spruce-fir forest reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the spruce-fir forest was >200 years since stand origin, although at any point in time this varied from <27% to >74% (Figure-survivorship). On average, 35% of the spruce-fir forest survived to >300 years, 5% survived to >630 years, and a very small percentage (~1%) survived a stand-replacing disturbance for >800 years. This highlights the stochastic nature of disturbances, in which some areas by chance alone escaped catastrophic disturbance for very long periods.


      The distribution of area among stand conditions within spruce-fir forest fluctuated markedly over time, as expected (Figure-conditions). For example, the percentage of spruce-fir forest in late-seral stages (i.e., understory reinitiation and shifting mosaic conditions) varied from 32% to 84%, reflecting the extremely dynamic nature of this high elevation forest cover type when considered over century-long periods. Due to the large fluctuations, it was not clear whether the seral-stage distribution achieved dynamic equilibrium over the 800-year simulation period (i.e., the percentage of spruce-fir forest in each stand condition did not reach a perfectly stable mean). This likely reflects the relatively long rotation period (300-350 years) of the major stand-replacing disturbance process (i.e., wildfire) relative to the simulation length (800 years). The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area, core area and the proximity index (a measure of patch isolation) exhibited the greatest variability over time.


      Our estimate of the current seral-stage distribution was almost never observed under the simulated HRV (Figure-hrv). Specifically, the current landscape contains only 6% of this cover type in the stand initiation condition, yet this situation was almost never observed under the simulated HRV (~0th percentile of the HRV distribution), and 32% in the stem exclusion condition, yet 93% of the time there was less than this amount under the simulated HRV. However, the current landscape contains a preponderance (62%) of spruce-fir forest in the late-seral stages (i.e, understory reinitiation and shifting mosaic conditions), and this situation was quite common under the simulated HRV (59th percentile of the HRV distribution). Overall, based on the four separate stand conditions (i.e., without aggregating the late-seral stages), the seral-stage departure index was 93% (Table-hrv). When the late-seral stages were aggregated, the seral-stage departure index declined dramatically to 57%. The current seral-stage configuration deviated substantially (86%) from the simulated HRV, although there was considerable variation (50-100% deviation) among metrics. Unfortunately, the nature of the configuration departure varied depending on whether the late-seral stages were treated separately or combined into a single class. Thus, the only reliable conclusion we can reach is that, in general, the current landscape contains fewer, smaller and geometrically less complex and more isolated patches of early-seral forest than existed under the simulated HRV.


Spruce-Fir with Aspen Forest [cover type description]


      In general, the vegetation dynamics in spruce-fir-aspen forest were very similar to those of spruce-fir forest. Nevertheless, we provide a complete description of the results for this cover type below and highlight the notable differences.


      Spruce-fir-aspen forest is much less common than spruce-fir forest on the SJNF, encompassing 67,500 ha and comprising roughly 8% of the Forest, but is nevertheless one of the dominant cover types (Table-areal coverage). The frequency and extent of simulated wildfires in spruce-fir-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). In almost half of the decades, less than 1% of the spruce-fir-aspen forest burned, inclusive of both high- and low-mortality affected areas. However, on average, almost once per 70 years, >10% of the area burned, and roughly once every 200-300 years, >20% of the spruce-fir-aspen forest burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied widely from 38 years to >800 years, with a mean and median of 220 years and 267 years, respectively, although almost no eligible area (<1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval was on average roughly 50 years shorter than observed for spruce-fir forest; largely reflecting the slightly lower average elevation of the spruce-fir-aspen type. As expected, return intervals varied spatially across the forest (Figure-map). In general, return intervals increased with elevation, reflecting the moister, cooler conditions at higher elevations. In addition, spruce-fir-aspen stands embedded in a neighborhood containing cover types with shorter return intervals (e.g., aspen, mountain shrubland) exhibited shorter return intervals, reflecting the importance of landscape context on fire regimes.


      The frequency and extent of simulated spruce beetle epidemics in spruce-fir-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). In almost half of the decades, less than 1% of the spruce-fir-aspen forest was disturbed, inclusive of both high- and low-mortality affected areas. However, on average, roughly twice per 100 years, >10% of the area was disturbed, and perhaps once every 400 years, >40% of the spruce-fir-aspen forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied widely from 50 years to >800 years, with a mean and median of 170 and 160 years, respectively, although very little eligible area (2%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval was on average roughly 50 years longer than observed for spruce-fir forest; reflecting the slightly reduced susceptibility of spruce-fir-aspen stands because of the lower density of the host species (Picea engelmannii). Not surprisingly, the return interval varied spatially across the forest and exhibited a highly contagious or clumped distribution (Figure-map). In general, the areas of most extensive and connected spruce-fir-aspen forest exhibited the shortest return intervals, but there was considerable variation among runs owing to the stochastic nature of spruce beetle outbreaks.


      The frequency and extent of simulated spruce budworm epidemics in spruce-fir-aspen forest varied markedly among decades (Figure-initiations, Figure-extent). In almost two-thirds of the decades, spruce budworm populations were at endemic levels and none of the spruce-fir-aspen forest was disturbed. However, roughly 3 times per 100 years, epidemics occurred affecting >10% of the area. Approximately once every 400 years, 50% of the spruce-fir-aspen forest was disturbed (Figure-recurrence). The return interval between epidemics (of any mortality level) at a single location varied from 36 years to >800 years, with a mean and median of 108 and 114 years, respectively, although almost no eligible area (<1%) escaped disturbance altogether over the course of an 800-year simulation (Figure-return). The return interval was very similar to that observed for spruce-fir forest because the stand conditions most susceptible to spruce budworm [i.e., understory reinitiation and shifting mosaic] are very similar for these two cover types. In particular, the aspen component (non-host species) declines to mere remnant status in the late understory reinitiation and shifting mosaic stages in the spruce-fir-aspen type, so that the density of preferred host trees (Abies lasiocarpa) is very similar between these cover types when in these stages. The return interval varied spatially across the forest, but at a very fine grain and in a seemingly random pattern (Figure-map).


      The age structure and dynamics of spruce-fir-aspen forest reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest trees in the stand. On average (over time), roughly 50% of the spruce-fir-aspen forest was >160 years since stand origin, although at any point in time this varied from <29% to >77% (Figure-survivorship). On average, 28% of the spruce-fir-aspen forest survived to >300 years, 5% survived to > 560 years, and a very small percentage (<1%) survived a stand-replacing disturbance for >800 years. This highlights the stochastic nature of disturbances, in which some areas by chance alone escaped catastrophic disturbance for very long periods. Overall, spruce-fir-aspen forest survived fewer years before another stand-replacing disturbance than did spruce-fir forest. The median age of spruce-fir-aspen forest, for example, was 40 years younger than for spruce-fir forest.


      The distribution of area among stand conditions within spruce-fir-aspen forest fluctuated markedly over time, as expected (Figure-conditions). For example, the percentage of spruce-fir-aspen forest in the late-seral condition (i.e., understory reinitiation and shifting mosaic stages) varied from 43% to 93%, reflecting the extremely dynamic nature of this high elevation forest cover type when considered over century-long periods. Due to the large fluctuations, it was not clear whether the seral-stage distribution achieved dynamic equilibrium over the 800-year simulation period (i.e., the percentage in each stand condition did not reach a stable mean). This likely reflects the relatively long rotation period (250-300 years) of the major stand-replacing disturbance process (i.e., wildfire) relative to the simulation length (800 years). The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area, core area and the proximity index (a measure of patch isolation) exhibited the greatest variability over time.


      Our estimate of the current seral-stage distribution was almost never observed under the simulated HRV (Figure-hrv). Specifically, the current landscape contains only 1% and 8% of this cover type in the stand initiation and stem exclusion conditions, respectively, yet this situation was uncommon under the simulated HRV (5th and 3rd percentiles, respectively, of the HRV distribution). The paucity of spruce-fir-aspen forest in the stem exclusion condition compared to the reverse situation in spruce-fir forest likely reflects differences in succession between these two cover types. In the spruce-fir-aspen type, the stem exclusion stage is dominated by aspen, and therefore succession to the understory reinitiation stage of development is dictated by the rapid rate of maturity and senescence of the relatively short-lived aspen. Thus, spruce-fir-aspen stands succeed to the understory reinitiation condition much sooner than spruce-fir stands. Due to the lack of large disturbances over the past century, most of the spruce-fir-aspen forest has already succeeded to the understory reinitiation or shifting mosaic stages, whereas much of the spruce-fir forest still remains in the stem exclusion stage. Consequently, the current landscape contains a preponderance (92%) of spruce-fir-aspen forest in the late-seral stages (i.e, understory reinitiation and shifting mosaic conditions), a situation almost never observed under the simulated HRV. Overall, based on the four separate stand conditions (i.e., without aggregating the late-seral stages), the seral-stage departure index was 92% (Table-hrv) - almost identical to that observed for spruce-fir forest. When the late-seral stages were aggregated, the seral-stage departure index declined slightly to 89%. The current seral-stage configuration deviated substantially (70%) from the simulated HRV, although there was considerable variation (40-98% deviation) among metrics and, in general, the departure was less than observed for spruce-fir forest. Unfortunately, the nature of the configuration departure varied depending on whether the late-seral stages were treated separately or combined into a single class. Thus, we were unable to reach any reliable conclusions regarding configuration departure in the late-seral stages. In addition, there does not appear to be any consistent and strong pattern of configuration departure in the early- or mid-seral stages for this cover type, although there is some indication that the current landscape contains fewer, smaller and geometrically less complex and more isolated patches of early- and mid-seral forest than existed under the simulated HRV.


Mesic Sagebrush [cover type description]


      Mesic sagebrush is relatively uncommon on the SJNF, encompassing 11,243 ha and comprising only ~1% of the Forest (Table-areal coverage). The frequency and extent of simulated wildfires in mesic sagebrush varied markedly among decades (Figure-initiations, Figure-extent). In roughly three out of every four decades, >10% of the mesic sagebrush burned, inclusive of both high- and low-mortality affected areas, and roughly once per 100 years, >40% of the area burned (Figure-recurrence). Under this wildfire regime, the return interval between fires (of any mortality level) varied from 24 to 800 years, with a mean and median of 55 years and 53 years, respectively, and essentially no mesic sagebrush escaped disturbance altogether over the course of an 800-year simulation (Figure-return). As expected, return intervals varied spatially across the forest (Figure-map), however the patterns were not explainable by any discernable factors, with the possible exception that mesic sagebrush patches embedded in a neighborhood containing cover types with shorter return intervals (e.g., ponderosa pine and mountain shrubland) exhibited shorter return intervals, whereas those patches surrounded by cover types with longer return interval (e.g., pinyon-juniper woodlands and cool moist mixed-conifer forest) exhibited longer return intervals. Thus, landscape context appeared to have an important influence on wildfire return intervals in mesic sagebrush.


      The age structure and dynamics of mesic sagebrush reflected the interplay between disturbance and succession processes. The survivorship distribution represents the percent of stands that survived to any age, where age represents time since stand origin, not necessarily the age of the oldest individuals in the stand. On average (over time), roughly 50% of the mesic sagebrush was >30 years since stand origin, although at any point in time this varied from <15% to >90% (Figure-survivorship). On average, 14% of the mesic sagebrush survived to >100 years and <3% survived a stand-replacing disturbance for >200 years. This highlights the stochastic nature of disturbances, in which some areas by chance alone escaped catastrophic disturbance for relatively long periods.


      The distribution of area among stand conditions within mesic sagebrush fluctuated markedly over time, as expected (Figure-conditions). For example, the percentage in the shrubs-herbs condition varied from 11% to 68%, reflecting the extremely dynamic nature of this cover type when considered over century-long periods. The seral-stage distribution appeared to be in dynamic equilibrium (i.e., the percentage in each stand condition varied about a stable mean), despite the fact that the proportion in herbs-shrubs versus shrubs-herbs during any snapshot (i.e., time step) varied considerably over time. The spatial configuration of stand conditions fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among configuration metrics (Table-hrv). Patch area, core area and the proximity index (a measure of patch isolation) exhibited the greatest variability over time and, in general, the shrub-herb stage was more dynamic than the herb-shrub stage.


      Our estimate of the current seral-stage distribution (83% in herb-shrub condition, 17% in shrub-herb condition) was infrequently observed under the simulated HRV (Figure-hrv). In most decades there was greater equity between stand conditions. Overall, the seral-stage departure index was 83% (Table-hrv). The current seral-stage configuration deviated substantially (58%) from the simulated HRV, although there was considerable variation (0-100% deviation) among metrics. WARNING, due to the lack of reliable field data on current stand age and condition in this cover type, these findings must be viewed with extreme caution. Until more complete data are obtained, we are unable to reach firm conclusions regarding HRV departure for this cover type.


Landscape structure


      Landscape composition, measured as the proportion of the landscape in each of 57 distinct and dynamic patch types (defined by unique combinations of cover type and stand condition), fluctuated markedly over time (Table-hrv). The average coefficient of variation (representing the 90 percentile range of variation about the median) across patch types was 131%, although it ranged broadly from 32% to 746%. There were no obvious discernable factors (e.g., cover type, seral stage, elevation) explaining the variability among patch types; however, the less common patch types (i.e., those comprising a smaller proportion of the landscape on average over time) were more likely to exhibit the greatest variability over time (Figure-cv). Interestingly, despite the high degree of dynamism exhibited by most patch types, the overall diversity of the mosaic, as represented by the Simpson’s diversity index (which is a function of the number of patch types and the equatability in the distribution of area among patch types), was surprisingly stable with a coefficient of variation of only 1%.


      Landscape configuration, measured by 19 different metrics that characterize the spatial character and arrangement, position, or orientation of patches within the landscape, was much less dynamic than landscape composition (Table-hrv). The average coefficient of variation across metrics was only 25% (range 1-73%). There were a couple of notable patterns of variation. First, metrics associated with patch size (e.g., area, core area, density) and isolation (e.g., proximity index) were more dynamic than metrics associated with patch geometry (e.g., shape, core area index) and edge contrast. Thus, the principal dynamics were associated with the grain of the patch mosaic. Second, in general, the area-weighted metrics were more dynamic than their unweighted counterparts. The area-weighted metrics give more weight to the larger patches when calculating the mean and are therefore not influenced greatly by variations affecting small patches. Thus, these metrics are less affected by the fine-grained heterogeneity created by the disturbance processes (e.g., abundant, small scattered patches) and provide a better overall measure of changes in the coarse-grain structure of the landscape. Taken in aggregate, these results suggest that the principal dynamics were associated with changes in the size and continuity of the large patches in the landscape; i.e., that large contiguous patches were periodically broken up (fragmented) by disturbance events but eventually coalesced to reform a coarse-grain mosaic, only to be broken up again.


      The current landscape structure deviates substantially (84% departure index) from the simulated HRV, and departure is much greater for the spatial configuration of the landscape (91% departure index) than the composition of the landscape (76% departure index) (Table-hrv). With respect to the composition of the landscape, more than half of the patch types (29/57) are completely outside their HRV (i.e., 100% departure index), while roughly one-sixth of the patch types (9/57) are within their 25-75th percentile range of variation (i.e., 0% departure index). When the late-seral stages (i.e., understory reinitiation and shifting mosaic) are combined into a single, aggregated “late-seral” stage within each forest cover type to reflect the inadequate discrimination between these conditions in the current landscape database, the proportion of patch types completely outside their HRV declines to one-third (16/48) and the landscape composition departure index declines to 68% (Table-hrv-combined). The principal cause of the decline is the change in departure for ponderosa pine-oak forest and spruce-fir forest. In both cases, our estimates of the current percentage of the landscape (or cover type) in the separate understory reinitiation and shifting mosaic conditions are completely outside their simulated HRV (i.e., 100% departure index); whereas, the combined late-seral stages are both well within their respective 25-75th percentile ranges of variation (i.e., 0% departure index).


      With respect to the configuration of the landscape, most of the metrics (15/19) are completely outside their HRV (i.e., 100% departure index) and two others are nearly so, while only one metric (interspersion and juxtaposition index) is completely within its 25-75th percentile range of variation (i.e., 0% departure index) (Table-hrv). In general, the current landscape contains fewer, larger, more extensive and less isolated patches than existed under the simulated HRV. The larger patches in the current landscape also tend to be geometrically less complex and contain proportionately more core area than existed under the simulated HRV. As a result, the current landscape contains much less edge than existed under the simulated HRV, but the edge that exists has higher average contrast than observed under the HRV. This latter finding is likely due to the fact that most of the edge in the current landscape is derived from abutting patches of different cover types and often involves high-contrast edges between forest and nonforest cover types (e.g., water, barren); whereas, under the simulated HRV, proportionately more of the edge is due to abutting patches of different seral stages of the same or similar cover types - which have lower contrast. Overall, the current landscape is more contagious and less structurally diverse than ever existed under the simulated HRV.


Habitats of Special Interest


      In addition to the 23 distinct vegetation types, we also defined several new classes based on aggregations of particular cover types and stand conditions (seral stages) for purposes of FRAGSTATS landscape pattern analysis (see FRAGSTATS - Analyses). These new classes represented ‘habitats of special interest’ to land managers. In the sections below, we briefly describe the spatial and temporal variability of each habitat over time under the HRV scenario. Note, these results were based entirely on the landscape pattern metrics computed using FRAGSTATS.


High Elevation Late-seral Conifer Forest


      High elevation late-seral conifer forest comprised anywhere from roughly 17% to 34% of the landscape over time under the simulated HRV and thus was a dominant feature of the landscape at all times (Table-hrv). The spatial configuration of this class varied markedly over time, although there was considerable variation in the magnitude of variability among metrics. The area-weighted versions of mean patch size, radius of gyration, core area, proximity index and shape index exhibited the greatest variability; all had coefficients of variability >100%. Despite the high variability of these metrics, their absolute values paint a picture of a very coarse-grained mosaic of geometrically complex patches maintained over time. The median area-weighted mean patch size, for example, was more than 20,000 ha, with a median traversability (i.e., radius of gyration) of more than 6 km and a median shape index of more than 18. Interpreted in combination with the unweighted metrics, these results indicate that this habitat was broadly distributed across the landscape at all times and contained a mixture of large, contiguous patches resulting from prolonged disturbance-free periods intermixed with numerous small (e.g., 10's of hectares) remnant patches embedded within or surrounded by younger successional stands. It is important to note that even though the habitat mosaic was coarse-grained and dominated by a relatively smaller number of very large patches, the mosaic shifted in space over time such that the location of the large patches varied over the course of the 800-year simulation.


      High elevation late-seral conifer forest comprises roughly 30% of the current landscape, which is the 93rd percentile of the HRV distribution (Table-hrv). This represents a 73% departure index. The current configuration deviates substantially from the simulated HRV, although there was considerable variation (0-100% departure) among metrics. In general, the unweighted versions of most metrics exhibited 100% departure, whereas the area-weighted versions were typically well within their 25-75th percentile ranges of variation (i.e., 0% departure). This was due to the absence of numerous small remnant patches in the current landscape that made up a large portion of the patches in the simulated landscape. Overall, it appears that the coarse configuration of this habitat in the current landscape is well within the simulated range of variation, but that the fine-scale heterogeneity is lacking.


Aspen-dominated Forest


      The seral-stage distribution in aspen-dominated forest fluctuated markedly over time, as expected (Table-hrv). At times, this habitat was a dominant feature of the landscape. On average, roughly 9% of the landscape was comprised of aspen-dominated forest, which is more than three times what can be accounted for by pure aspen forest alone. Thus, the early seral stages of the mixed conifer-aspen forest types accounted for more than two-thirds (on average, and considerably more at times) of the aspen present in the landscape at any point in time. The spatial configuration of seral stages fluctuated markedly over time as well, although there was considerable variation in the magnitude of variability among metrics. Patch area, core area and the proximity index (a measure of patch isolation), and especially the area-weighted versions of these metrics, exhibited the greatest variability over time, with coefficients of variability typically >>100%. In general, the early-seral stage was most dynamic, followed by the mid-seral stage and late-seral stage. This was not too surprising since the early- and mid-seral stages were influenced by the promotion of aspen following disturbances in the mixed conifer-aspen stands, yet the late-seral stage was restricted to pure aspen forest only. Accordingly, while the area-weighted mean patch size of late-seral aspen forest varied from roughly 80 to 320 ha over time, the early- and mid-seral stages varied from roughly 10 to 2,900 ha and 80 to 2,700 ha over time, respectively. Interpreted collectively, these metrics paint a picture of a highly dynamic distribution of aspen-dominated forest over time, in which late-seral patches were relatively small and isolated (being restricted in space by the distribution of pure aspen forest), while early- and mid-seral stages fluctuated dramatically over time, expanding to encompass large, contiguous and geometrically complex patches for an 80- to 120-year period following large stand-replacing disturbances, and contracting after the conifers regained dominance of the stands.


      Our estimate of the current seral-stage distribution of aspen-dominated forest was infrequently observed under the simulated HRV, producing a seral-stage departure index of 88% (Table-hrv). Specifically, the current landscape contains too little in the early- and mid-seral stages and too much in the late-seral stage compared to the HRV. The current seral-stage configuration deviated much less (54% departure) from the simulated HRV, although there was considerable variability (0-97% departure) among metrics. In general, the unweighted versions of most metrics exhibited a high degree of departure, whereas the area-weighted versions exhibited little to no departure. This was due to the absence of many small patches in the current landscape that made up a large portion of the patches in the simulated landscape. In general, if we ignore the discrepancies due to small patches (missing in the current landscape), then the current configuration of aspen-dominated forest appears to be well within the simulated range of variation, with one exception - the mid-seral stage patches in the current landscape are geometrically less complex, contain proportionately more core area (as a result), and are more isolated from each other than existed under the simulated HRV.


Low Elevation Fire-maintained Open Canopy Forest


      Low elevation fire-maintained open canopy forest comprised anywhere from roughly 9% to 16% of the landscape over time under the simulated HRV and thus was a dominant feature of the landscape at all times (Table-hrv). The spatial configuration of this class varied markedly over time, although there was considerable variation in the magnitude of variability among metrics. The area-weighted versions of mean patch size, core area and proximity index exhibited the greatest variability; all had coefficients of variability >100%. Despite the high variability of these metrics, their absolute values paint a picture of a fairly coarse-grained mosaic of geometrically complex patches maintained over time. The median area-weighted mean patch size, for example, was more than 2,000 ha, with a median traversability (i.e., radius of gyration) of roughly 2 km and a median shape index of more than 12. Interpreted in combination with the unweighted metrics, these results indicate that this habitat was broadly distributed across the low elevation ponderosa pine zone at all times and contained a mixture of large, contiguous patches maintained by frequent low-mortality fires intermixed with numerous smaller (e.g., 10's of hectares) patches interspersed with a mixture of young successional stands and late-seral stands in the shifting mosaic condition. The large patches were located wherever there were large contiguous areas of ponderosa pine, e.g., on mesas in relatively unbroken terrain. The smaller patches were more likely to be found where the ponderosa pine intermixed with pinyon-juniper woodlands, mountain shrublands, pure aspen forest, and cool, moist mixed-conifer forest where fires were less frequent (thus allowing the ponderosa pine to succeed to the shifting mosaic condition more often) or more severe (thus causing stand replacement). Overall, the configuration of low elevation fire-maintained open canopy forest was relatively stable (compared to other classes), as it was driven strongly by the distribution of the relatively persistent larger patches.


      Low elevation fire-maintained open canopy forest is absent from the current landscape. This represents a 100% departure index and is in fact well below the minimum percentage of the landscape (9%) observed under the simulated HRV (Table-hrv). The class configuration departure is undefined since the class is absent from the current landscape.


Oak-serviceberry-dominated Shrublands


      The seral-stage distribution in oak-serviceberry-dominated shrublands fluctuated moderately over time, as expected (Table-hrv). This habitat was a dominant feature of the landscape at all times owing to the preponderance of mountain shrublands, which comprise roughly 14% of the landscape. Given the scarcity of pinyon-juniper-oak-serviceberry woodlands (1.15% of landscape) and the paucity of stand-replacing disturbances in ponderosa pine-oak forest, the vast majority of oak-serviceberry-dominated shrublands were maintained as persistent mountain shrublands. Thus, the principal dynamic was the shifting distribution between early- and late-seral stages. The spatial configuration of seral stages fluctuated moderately over time as well, although there was considerable variation in the magnitude of variability among metrics. The area-weighted versions of patch area, core area and the proximity index (a measure of patch isolation) exhibited the greatest variability over time, with coefficients of variability >100%, although many of the metrics had remarkably low coefficients of variability. In general, the early-seral stage was slightly more dynamic than the late-seral stage. This was not too surprising since the early-seral stage was influenced by the promotion of oak-serviceberry following disturbances in pinyon-juniper-oak-serviceberry woodland and ponderosa pine-oak forest, but the late-seral stage was restricted to mountain shrubland only. Accordingly, while the area-weighted mean patch size of late-seral aspen forest varied from roughly 200 to 1,000 ha over time, the early-seral stage varied from roughly 200 to 2,000 ha over time. Interpreted collectively, these metrics paint a picture of a relatively balanced shifting mosaic (over time) of early- and late-seral shrublands, in which occasionally, following large-scale disturbances, early-seral patches would predominate and form relatively large, contiguous patches.


      Our estimate of the current seral-stage distribution of oak-serviceberry-dominated shrubland was never observed under the simulated HRV, producing a seral-stage departure index of 100% (Table-hrv). The current seral-stage configuration deviated much less dramatically but still substantially (76% departure) from the simulated HRV, although there was considerable variability (31-100% departure) among metrics. In general, the unweighted versions of most metrics exhibited a high degree of departure, whereas the area-weighted versions exhibited little departure. This was due to the absence of many small patches in the current landscape that made up a large portion of the patches in the simulated landscape. This was particularly true for the early-seral stage configuration, which fell within the 25-75th percentile range of variation (i.e., 0% departure) for most area-weighted metrics. WARNING, due to the lack of reliable field data on current stand age and condition in the mountain shrubland and pinyon-juniper woodland cover types, these findings must be viewed with extreme caution. Until more complete data are obtained, we are unable to reach firm conclusions regarding HRV departure for this habitat type.


Sagebrush-dominated Shrublands


      Sagebrush-dominated shrubland comprised anywhere from roughly 1.5% to 2.7% of the landscape over time under the simulated HRV and thus was never a dominant feature of the landscape (Table-hrv). The minimum coverage was governed by the areal extent of mesic sagebrush cover, which comprised 1.3% of the landscape. Variability in extent above this lower threshold was governed by the frequency and extent of high-mortality wildfires in pinyon-juniper-sagebrush woodlands, which comprised an additional 1.9% of landscape. Thus, the maximum possible extent of this habitat was 3.2% of the landscape, but this could only occur if 100% of the pinyon-juniper-sagebrush was burned within a 50-year period, an unlikely event given the broad spatial distribution of this cover type. The spatial configuration of this class varied markedly over time, although there was considerable variation in the magnitude of variability among metrics. Interestingly, in contrast to most other patch types (e.g., cover types, habitat types), the area-weighted metrics associated with patch size, radius of gyration, core area and proximity index were not more variable than their unweighted counterparts, and the proximity index was the only metric with a coefficient of variability >100%. The absolute values of these metrics paint a picture of a fairly coarse-grained mosaic of geometrically complex patches maintained over time. The area-weighted mean patch size, for example, ranged from roughly 600 to 1,300 ha, with a median traversability (i.e., radius of gyration) of more than 1 km and a median shape index of more than 4. Overall, the configuration metrics indicate that this habitat was broadly distributed across the landscape at all times, anchored by the distribution of persistent mesic sagebrush cover, and consisted of mostly moderately sized but scattered (and therefore somewhat isolated) patches of persistent mesic sagebrush combined with periodic pulses of more extensive sagebrush following stand-replacing disturbances in pinyon-juniper-sagebrush woodlands.


      Sagebrush-dominated shrubland comprises roughly 1.9% of the current landscape, which is the 35th percentile of the HRV distribution (Table-hrv). This represents a 0% departure index. The current configuration deviated moderately (54% departure) from the simulated HRV, although there was considerable variation (0-100% departure) among metrics. Not surprisingly, the current landscape contains fewer, geometrically less complex and more aggregated patches (and less edge as a result) than existed under the HRV distribution, but the overall grain of the mosaic as measured by the area-weighted mean patch size and correlation length (area-weighted mean radius of gyration) was well within the 25-75th percentile range of variation (i.e., 0% departure). Overall, it appears that the coarse configuration of this habitat in the current landscape is well within the simulated range of variation, but that the fine-scale heterogeneity is lacking.


Wildlife Indicator Species


      We selected four wildlife indicator species with uniquely different habitat associations and life history attributes to predict how a wide range of wildlife species might respond to changes in habitat conditions resulting from disturbance and succession processes over time (see HABIT@ - Species Models). In the sections below, for each indicator species we briefly describe the spatial and temporal variability in habitat capability under the HRV scenario and the degree of departure of the current landscape. Note, these results are not especially revealing as such because they represent a single disturbance scenario. The power of the habitat capability analysis resides in its use in comparing among alternative disturbance scenarios; e.g., comparing habitat capability between the HRV scenario and one or more land management scenarios. Indeed, this is our intended use in the next phase of this project.


Pine marten


      Pine marten are year-round residents that prefer the interior portions of late-successional, high-elevation conifer forests (principally spruce-fir and cool moist mixed-conifer forest) for foraging and denning. We included the pine marten as an example of a habitat specialist associated with late-successional high-elevation conifer forests, and expected habitat capability for this species to be quite sensitive to stand-replacing disturbances, especially those resulting in the fragmentation of contiguous late-successional forest and concomitant loss of interior habitat.


      Surprisingly, the landscape capability index was relatively stable over time at the scale of the Columbine District (Figure-LC index), fluctuating between 218-336 and exhibiting a 27% coefficient of variation (Table-LC index). Apparently, the highly contagious spatial pattern in vegetation successional stages imposed by the dominant stand-replacing disturbance process in high-elevation conifer forests (i.e., wildfire) maintained large patches of interior forest habitat needed by this species. Thus, while the vegetation mosaic was clearly shifting over time in response to disturbance and succession, a relatively stable amount of pine marten habitat was provided for somewhere in the landscape at all times.

 

Pine Marten Movie - Click here to download a movie depicting the shifting mosaic in habitat capability for this species on the Columbine District over an 800-year simulation under the HRV scenario. This is a spatial representation of the habitat capability index that is summarized in the landscape capability index reported above. NOTE, this is a 30 Mb Microsoft Media file (.avi) that requires appropriate movie viewing software (e.g., Quick Time Player).


The pine marten landscape capability response curve is an alternative way of summarizing the fluctuations in the LC index (Figure-LC response) that is particularly useful for comparing among scenarios; it is provided here as a reference for future comparisons with alternative land management scenarios.


      The current landscape contains more pine marten habitat than was typically observed under the simulated HRV, although it is not completely outside the simulated range of variation (Table-LC index). This is not surprising given the species’ preference for interior high-elevation conifer forests and our findings on HRV departure for high-elevation conifer forests. As already noted, the current landscape has fewer, larger, more extensive and less isolated patches of late-seral conifer forest than existed under the simulated HRV. This translates directly into abundant suitable habitat for pine marten.


Three-toed Woodpecker


      Three-toed woodpeckers are year-round residents that inhabit late-successional, high-elevation conifer forests, similar to pine marten, but reach peak densities for a period of five to seven years following wildfires and severe bark beetle outbreaks in conifer (and to a lesser extent aspen) stands. We included the three-toed woodpecker as an example of a species associated with transient post-disturbance habitats, and expected habitat capability for this species to vary dramatically, spatially and temporally, in response to wildfire and bark beetle disturbances.


      As predicted, the landscape capability index varied considerably over time at the scale of the Columbine District (Figure-LC index), fluctuating between 1048-1845 and exhibiting a 46% coefficient of variation (Table-LC index). The dramatic fluctuations in habitat capability reflected the periodic pulses of high quality habitat following large-scale disturbance events in the mid- and high-elevation conifer forests. In addition, as expected, the peaks in habitat capability were usually short-lived (i.e., one time step) and followed by a rapid return to the pre-disturbance habitat capability level. Given the rapid response in habitat capability to disturbances, this species would be a particular good indicator of alterations to the disturbance regime.

 

Three-toed Woodpecker Movie - Click here to download a movie depicting the shifting mosaic in habitat capability for this species on the Columbine District over an 800-year simulation under the HRV scenario. This is a spatial representation of the habitat capability index that is summarized in the landscape capability index reported above. NOTE, this is a 32 Mb Microsoft Media file (.avi) that requires appropriate movie viewing software (e.g., Quick Time Player).


The three-toed woodpecker landscape capability response curve is an alternative way of summarizing the fluctuations in the LC index (Figure-LC response) that is particularly useful for comparing among scenarios; it is provided here as a reference for future comparisons with alternative land management scenarios.


      The current landscape contains an abundance of three-toed woodpecker habitat, but at a level that was often realized under the simulated HRV (Table-LC index). The 8% departure index for the Columbine District is not too surprising given that this species utilizes late-seral high-elevation conifer forests, similar to the pine marten, which is in abundant supply in the current landscape. The higher levels of habitat that were occasionally observed under the simulated HRV corresponded to brief periods of exceptional habitat conditions following large disturbances.


Olive-sided Flycatcher


      Olive-sided flycatchers are neotropical migrants that select high-contrast edges between early- and late-successional, mid- and high-elevation conifer forests. We included the olive-sided flycatcher as an example of an edge specialist, and expected habitat capability for this species to fluctuate widely in response to the changing amount and distribution of high-contrast edges created by stand-replacing disturbances.


      As predicted, the landscape capability index varied somewhat over time at the scale of the Columbine District (Figure-LC index), fluctuating between 4351-7565 and exhibiting a 33% coefficient of variation (Table-LC index). The fluctuations in habitat capability reflected the periodic pulses of high-quality edge habitat following large-scale disturbance events in the mid- and high-elevation conifer forests. In particular, the heterogeneous pattern of tree mortality following both wildfire and insect outbreaks resulted in an abundance of ideal edge habitat for this species. Interestingly, the coefficient of variation in the landscape capability index was intermediate between the pine marten (lower) and three-toed woodpecker (higher). This was likely due to the relatively consistent supply of high-contrast edges bordering permanent openings such as meadows, barren areas, and lakes and ponds that acted like a buffer against major fluctuations in available habitat. In addition, in contrast to the very transient nature of three-toed woodpecker habitat following disturbances, high-quality olive-sided flycatcher habitat tended to slowly degrade over several decades in response to the gradual succession process operating in the disturbance opening. Given the recent emphasis on fragmentation-sensitive species, which often involves avoiding creating high-contrast edges, this species would be a particularly good indicator of habitat conditions likely to be jeopardized by a narrow focus on fragmentation-sensitive species.

 

Olive-sided Flycatcher Movie - Click here to download a movie depicting the shifting mosaic in habitat capability for this species on the Columbine District over an 800-year simulation under the HRV scenario. This is a spatial representation of the habitat capability index that is summarized in the landscape capability index reported above. NOTE, this is a 32 Mb Microsoft Media file (.avi) that requires appropriate movie viewing software (e.g., Quick Time Player).


The olive-sided flycatcher landscape capability response curve is an alternative way of summarizing the fluctuations in the LC index (Figure-LC response) that is particularly useful for comparing among scenarios; it is provided here as a reference for future comparisons with alternative land management scenarios.


      The current landscape contains less olive-sided flycatcher habitat than was ever observed under the simulated HRV (Table-LC index). This is not surprising given the species’ preference for high-contrast edges and the paucity of recent disturbances. Much of the current high-quality habitat is associated with relatively permanent edges bordering water bodies, meadows and barren openings.


Elk


      Elk are year-round residents that undergo short-distance elevational migrations between summer and winter ranges. They are found in association with high-elevation conifer and aspen forests and subalpine meadows during the summer; preferring the conifer and aspen forests as hiding cover and using the forest openings and meadows for foraging. Stand-replacing disturbances have transient and opposite effects on foraging and hiding cover; initially increasing forage availability but decreasing hiding cover. Moreover, local resource requirements (for forage and cover) can be met in a wide variety of cover types. We included the elk as a generalist species that prefers a well-interspersed mosaic of early- and late-successional communities, and expected habitat capability for this species to be somewhat robust to vegetation changes caused by disturbance and succession processes.


      As predicted, the landscape capability index varied very little over time at the scale of the Columbine District (Figure-LC index), fluctuating between 71-102 and exhibiting a 29% coefficient of variation (Table-LC index). Note, the relatively low values of the landscape capability index for this species are potentially misleading. Recall that the landscape capability (LC) index places non-overlapping homeranges on the landscape until the landscape is saturated with homeranges and then randomly keeps or rejects each homerange based on the probability given by the homerange capability (HC) or population capability (PC) index value of the focal (center) cell. This results in the number of realized homeranges supported by the landscape (i.e. the LC index). However, this homerange tiling process does not provide an interpretable index value for non-territorial species like the elk. For social species such as the elk, this index grossly underestimates the potential number of individuals supported by the landscape. Instead, we used it here as a relative index of habitat capability. In this case, the index indicates that the shifting mosaic of vegetation successional stages over time provided a relatively stable amount of elk habitat well-distributed across the landscape at all times.

 

Elk Movie - Click here to download a movie depicting the shifting mosaic in habitat capability for this species on the Columbine District over an 800-year simulation under the HRV scenario. This is a spatial representation of the habitat capability index that is summarized in the landscape capability index reported above. NOTE, this is a 32 Mb Microsoft Media file (.avi) that requires appropriate movie viewing software (e.g., Quick Time Player).


The elk landscape capability response curve is an alternative way of summarizing the fluctuations in the LC index (Figure-LC response) that is particularly useful for comparing among scenarios; it is provided here as a reference for future comparisons with alternative land management scenarios.


      The current landscape contains substantially less elk habitat than was ever observed under the simulated HRV (Table-LC index). This is not surprising given the species’ preference for an interspersion of cover and forage. Optimal habitat conditions are provided by a heterogeneous mosaic of vegetation succession stages that provide both cover and forage in close proximity. Given the paucity of recent disturbances, the resulting coarse-grained vegetation mosaic offers comparatively few opportunities for these interspersion and juxtaposition requirements to be met.



Effects of Scale and Context


      We quantified the dynamics in landscape structure and wildlife habitat capability in relation to landscape extent (scale) and context (i.e., geographic location) by examining the relative variability and the degree of similarity in the observed range of values in landscape metrics among several sub-landscapes (Figure-map).


      As expected, the range of variability in landscape structure and wildlife habitat capability for selected indicator species increased with decreasing landscape extent (Figure-scale-land, Figure-scale-wildlife); smaller landscapes exhibited greater variability, or dynamism, over time. Not surprisingly, the variability in landscape structure among individual landscapes was greatest for the smallest extent (watershed). In other words, while the overall range of variability in landscape structure was consistently greater at the smallest extent, there was substantial variation among watersheds in the magnitude of their variability, indicating that landscapes become increasingly unique or idiosyncratic at smaller extents (see below). This was particularly evident for the landscape composition metrics, where the Narraguinnep watershed exhibited more than two-fold greater variability than the Hermosa and Piedra watersheds (Table-scale-land). Interestingly, while the Narraguinnep watershed was considerably more dynamic in composition than the other two watersheds, it was the most stable in terms of landscape configuration. Thus, while the seral-stage distribution fluctuated more dramatically in this watershed, the shifting mosaic of seral stages maintained a more stable spatial configuration.


      Despite the limitation of having only three landscape extents (watershed, District, and Forest), there was a strong indication of a nonlinear relationship between extent and variability (or dynamism). Specifically, the magnitude of variability in landscape structure increased only modestly as the landscape extent decreased from the forest scale (847,638 ha) to the district scale (average = 282,546 ha), but increased dramatically as the landscape extent decreased to the watershed scale (average = 38,469 ha). This nonlinear relationship was apparent for both the landscape composition metrics and the landscape configuration metrics (Table-scale-land), although the pattern was much more threshold-like for the landscape configuration metrics (Figure-scale-land). Specifically, there was little change in the variability of landscape configuration between the forest and district scales, but an abrupt increase in variability between the district and watershed scales. While the same threshold-like pattern was present for the landscape composition metrics, it was much less abrupt, as there was a small but notable increase in variability between the forest and district scales and then an abrupt increase in variability between the district and watershed scales that was due principally to high variability in the Narraguinnep watershed. A similar relationship was evident for three-toed woodpecker habitat capability, the only species for which we were able to complete the habitat capability analysis at all three scales, in which there was little change in variability between the forest and district scales and then an abrupt increase in variability between the district and watershed scales (Figure-scale-wildlife). Note, despite the apparent nonlinear relationship between extent and variability in landscape structure (and wildlife habitat capability), there was nonetheless still substantial variability at the forest scale. Indeed, the overall coefficient of variation in landscape composition at the forest scale was 131%. Moreover, based on the observed scaling relationship, we can infer (through extrapolation) that even larger extents would still exhibit substantial variability in landscape structure over time.


      Variability in landscape composition was consistently and considerably greater than the variability in landscape configuration at all scales (Table-scale-land). The average coefficient of variability in landscape composition metrics varied from 131% (Forest) to 831% (Narraguinnep watershed), whereas the average coefficient of variability in landscape configuration metrics varied from 25% (Forest) to 56% (Piedra watershed). In general, landscape composition was 3-6 times more variable than landscape configuration, indicating that while the composition of patch types (i.e., unique combinations of cover type and seral stage) across the landscape was highly dynamic, the spatial configuration of the patch mosaic was relatively stable at all scales.


      As expected, each landscape (district or watershed) differed in its absolute range of variability in landscape structure due to its unique landscape context. The average similarity (across metrics) among districts was 37% for composition and 48% for configuration (Table-context-district); among watersheds it was 22% for composition and 33% for configuration (Table-context-watershed). At both scales, the similarity was greater for landscape configuration than landscape composition, indicating that configuration metrics were less sensitive to landscape context than composition metrics. Also, the similarity among landscapes was lower at the watershed scale than at the district scale, suggesting that landscape context becomes increasingly important as the size of the landscape decreases - due to the increasingly unique ecological setting, whereas at large extents the local variability in landscape structure tends to average out.


      Although the magnitude of variability (CV’s) in each metric was generally similar across districts (Table-scale-land), the percent similarity in the absolute range of variability was highly variable among metrics (0-85% average similarity across comparisons; Table-context-district). A similar pattern was true for watersheds (0-90% average similarity across comparisons; Table-context-watershed). In other words, while different landscapes of similar extent were equally dynamic in a relative manner across in a wide range of metrics, the absolute range of variation varied markedly between landscapes for some metrics but not for others. Thus, some landscape metrics were particularly sensitive to landscape context. In general, the area-weighted patch metrics were more sensitive to landscape context (i.e., lower percent similarity) at both scales, suggesting that changes in the coarse-grained mosaic of patches (i.e., changes in the size and continuity of the large patches) contributed most to the differences among landscapes.


      Lastly, while the relative and absolute range of variability in landscape structure was strongly related to landscape extent and context, the degree of departure of the current landscape from the simulated HRV was not. The overall landscape structure departure index was remarkably consistent across landscapes at all extents, although the component landscape composition and configuration departure indices exhibited slightly different relationships (Table-scale-hrv; Figure-scale-hrv). Specifically, landscape composition departure exhibited no clear relationship with landscape extent, although the variability in departure among landscapes was greatest at the smallest extent. This is consistent with our finding above that smaller landscapes are increasingly unique in their context and therefore more likely to exhibit idiosyncratic behavior (in this case, departure). To our surprise, landscape configuration departure exhibited a positive relationship with landscape extent. Specifically, configuration departure was consistently lower for the three smaller watersheds (range77-84%) than the three larger districts (range 86-94%) and forest (91%). However, this pattern was possibly spurious as it was attributable to differences in only a few configuration metrics in two of the three watersheds. Most metrics exhibited 100% departure in all landscapes.


Historic Range of Variability Tables


      This section includes the complete set of HRV tables for the whole forest and each of the districts, including, for each extent, the landscape-level HRV table and a class-level HRV table for each cover type or habitat of special interest. Note, many of the tables associated with the whole forest were referenced in the previous sections. However, the tables for each of districts have not been referenced elsewhere. Given the number and variety of HRV tables listed below and the difficulty in understanding the relationship among these tables, it is essential to understand the basic organizational framework within which these tables were constructed.


      Landscape-level tables.–At the landscape level, the entire landscape (either the whole forest or one of the districts) is considered as a single patch mosaic comprised of many patch types (unique combinations of cover type and stand condition). The landscape composition metrics refer to the percentage of the landscape comprised of each patch type, while the landscape configuration metrics refer to the spatial character and arrangement, position, or orientation of patches within the landscape. The landscape table reports the range of variation and departure of the current landscape from the HRV for each metric, and provides a summary of the overall composition and configuration departure for the landscape.


      Class-level tables.–At the class level, each cover type is considered separately. The class composition metrics refer to the percentage of the landscape comprised of each stand condition class (or seral stage) associated with the corresponding cover type, while the class configuration metrics refer to the spatial character and arrangement, position, or orientation of these patches within the landscape. Thus, the class composition metrics are simply a subset of the landscape-level composition metrics - those of the corresponding cover type. The class configuration metrics, on the other hand, are uniquely different from the corresponding landscape metrics. The class configuration metrics represent the spatial character and arrangement, position, or orientation of a single patch type - a single condition class or seral stage of the corresponding cover type. In contrast, the landscape configuration metrics consider all patch types simultaneously. The class table reports the range of variation and departure of the current landscape from the HRV for each class metric, and provides a summary of the overall seral-stage and configuration departure for the corresponding cover type.


      Reclass tables.–At each organizational level (landscape and class) and for each landscape extent (whole forest and each district), we also reclassified cover types and stand conditions by aggregating patch types into a smaller set of classes in order to better represent certain habitats of special interest (and increased the minimum mapping unit from 0.065 ha to 0.5 ha). Here, the landscape mosaic was based on a redefined and smaller set of patch types of special interest and was represented at a coarser spatial resolution. The composition and configuration metrics at the landscape and class levels were computed from this redefined landscape for each landscape extent. These tables are flagged below as “reclass tables”.


Landscape Tables:

 

          San Juan National Forest

          Dolores District

          Columbine District

          Pagosa District

          San Juan National Forest (reclass table)

          Dolores District (reclass table)

          Columbine District (reclass table)

          Pagosa District (reclass table)                  

Class Tables:


      San Juan National Forest

 

          Pinyon-Juniper Woodland

          Pinyon-Juniper-Sagebrush

          Pinyon-Juniper-Oak-Serviceberry

          Mountian Shrubland

          Ponderosa Pine-Oak Forest

          Ponderosa Pine-Oak-Aspen Forest

          Warm-Dry Mixed-Conifer Forest

          Warm-Dry Mixed-Conifer with Aspen Forest

          Cool-Moist Mixed-Conifer Forest

          Cool-Moist Mixed-Conifer with Aspen Forest

          Pure Aspen Forest

          Spruce-Fir Forest

          Spruce-Fir with Aspen Forest

          Mesic Sagebrush

          High-elevation Conifer Forest (reclass table)

          Low-elevation Conifer Forest (reclass table)

          Pinyon-Juniper Woodlands Combined (reclass table)

          Aspen-dominated Stands (reclass table)

          Oak-dominated Stands (reclass table)

          Sagebrush-dominated Stands (reclass table)


      Dolores District

 

          Pinyon-Juniper Woodland

          Pinyon-Juniper-Sagebrush

          Pinyon-Juniper-Oak-Serviceberry

          Mountian Shrubland

          Ponderosa Pine-Oak Forest

          Ponderosa Pine-Oak-Aspen Forest

          Warm-Dry Mixed-Conifer Forest

          Warm-Dry Mixed-Conifer with Aspen Forest

          Cool-Moist Mixed-Conifer Forest

          Cool-Moist Mixed-Conifer with Aspen Forest

          Pure Aspen Forest

          Spruce-Fir Forest

          Spruce-Fir with Aspen Forest

          Mesic Sagebrush

          High-elevation Conifer Forest (reclass table)

          Low-elevation Conifer Forest (reclass table)

          Pinyon-Juniper Woodlands Combined (reclass table)

          Aspen-dominated Stands (reclass table)

          Oak-dominated Stands (reclass table)

          Sagebrush-dominated Stands (reclass table)


      Columbine District

 

          Pinyon-Juniper Woodland

          Pinyon-Juniper-Sagebrush

          Pinyon-Juniper-Oak-Serviceberry

          Mountian Shrubland

          Ponderosa Pine-Oak Forest

          Ponderosa Pine-Oak-Aspen Forest

          Warm-Dry Mixed-Conifer Forest

          Warm-Dry Mixed-Conifer with Aspen Forest

          Cool-Moist Mixed-Conifer Forest

          Cool-Moist Mixed-Conifer with Aspen Forest

          Pure Aspen Forest

          Spruce-Fir Forest

          Spruce-Fir with Aspen Forest

          Mesic Sagebrush

          High-elevation Conifer Forest (reclass table)

          Low-elevation Conifer Forest (reclass table)

          Pinyon-Juniper Woodlands Combined (reclass table)

          Aspen-dominated Stands (reclass table)

          Oak-dominated Stands (reclass table)

          Sagebrush-dominated Stands (reclass table)


      Pagosa District

 

          Pinyon-Juniper Woodland

          Pinyon-Juniper-Sagebrush

          Pinyon-Juniper-Oak-Serviceberry

          Mountian Shrubland

          Ponderosa Pine-Oak Forest

          Ponderosa Pine-Oak-Aspen Forest

          Warm-Dry Mixed-Conifer Forest

          Warm-Dry Mixed-Conifer with Aspen Forest

          Cool-Moist Mixed-Conifer Forest

          Cool-Moist Mixed-Conifer with Aspen Forest

          Pure Aspen Forest

          Spruce-Fir Forest

          Spruce-Fir with Aspen Forest

          Mesic Sagebrush

          High-elevation Conifer Forest (reclass table)

          Low-elevation Conifer Forest (reclass table)

          Pinyon-Juniper Woodlands Combined (reclass table)

          Aspen-dominated Stands (reclass table)

          Oak-dominated Stands (reclass table)

          Sagebrush-dominated Stands (reclass table)