HABIT@
Wildlife Habitat Capability Modeling Program
Species’ Models
This section provides a description of the indicator species selected for this analysis, including the method used to select species, a general description of each species’ relevant life history and habitat associations, and the detailed habitat capability model constructed using HABIT@.
Indicator Species Selection
We sought to select a small set of vertebrate 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 wildfire disturbance and succession processes over time (Hansen and Urban 1992). We sought to include both habitat generalists and habitat specialists. We defined ‘habitat generalist’ as a species associated with a wide range of environmental conditions. Because of their ability to utilize many different environments, we hypothesized that habitat generalists would not exhibit large responses to wildfire disturbance and successional processes. We defined ‘habitat specialist’ as a species associated with a relatively narrow range of environmental conditions. Because of this specialization, we hypothesized that habitat specialists would exhibit strong responses to wildfire disturbance and succession processes. We also distinguished between species that prefer open vs. closed forest structure (<60 vs. >60% canopy closure, respectively), species that prefer early vs. late forest seral stages (Oliver and Larson 1990, Spies 1997), and species that utilize single vs. multiple kinds of cover types.
To facilitate the selection of indicator species, we developed a wildlife habitat-relationships matrix based on the criteria discussed above. Specifically, we recognized three general types of habitat associations: single vegetation type, multiple vegetation types, and edges between two vegetation types. Under each association, vegetation types were classified by canopy closure and seral stage. Canopy closure was defined as being open (<60%) or closed (>60%), and seral stage was defined as early- or late-seral forests. Early-seral forests follow a major disturbance and are characterized by the establishment of new tree seedlings, release of surviving seedlings and saplings, and vegetative reproduction of injured shrubs and herbs (Spies 1997). Late-seral forests are composed of trees of many classes, including some old individuals (>200 yr). This stage is also characterized by a fine-grained pattern of small disturbance patches (death of individual canopy trees through disease, insects, or wind, as well as an accumulation of coarse woody debris on the forest floor (Spies 1997)). We further distinguished between forest interior and edge conditions.
Based on the wildlife-habitat relationships matrix, we surveyed seven knowledgeable wildlife biologists in the south-central Rocky Mountains and asked them to list vertebrate species that occur within the study area and utilize the kinds of habitat associations defined in the matrix. We also asked them to speculate on how species would be affected by different disturbance regimes. The survey produced a long list of potential vertebrate indicator species. From this list, we selected four that represent a broad diversity of habitat requirements and life histories: pine marten (Martes americana), elk (Cervus elaphus nelsoni), three-toed woodpecker (Picoides tridactylus), and olive-sided flycatcher (Contopus borealis). Briefly, pine marten is a habitat specialist associated with late-successional, interior spruce-fir forests; three-toed woodpecker is associated with transient post-fire habitats; elk is a habitat generalist found in association with high-elevation conifer and aspen forests and subalpine meadows during the summer; and olive-sided flycatcher is a neotropical migrant that selects high-contrast edges between early- and late-seral conifer forests. The details of each species’ life history and habitat requirements are important for the development of the habitat capability models (see below), but are not essential for understanding the general results and conclusions of this study. In some sense, the particular indicator species don’t really matter that much; they simply represent a range of possible species responses to the simulated landscape dynamics. Nevertheless, a detailed description of each species’ life history and habitat requirements are given below.
Indicator Species’ Descriptions
Pine Marten
Pine marten prefer the interior portions of late-successional high-elevation conifer forest (principally spruce-fir and cool moist mixed-conifer forests) for foraging and denning (Buskirk and Powell 1994). Marten appear to use structural components of mature forests to avoid predators (Drew 1995), to gain access to prey in winter (Hargis and McCullough 1984, Corn and Raphael 1992, Sherburne and Bisonette 1994) and to gain thermal advantages, especially while resting (Buskirk et al. 1989, Taylor 1993, Raphael and Jones 1997). Marten generally avoid habitats that lack overhead cover and avoid traveling >23 meters from forest edges, especially in winter (Koehler et al. 1990, Ruggerio et al. 1994). Marten also appear to respond negatively to habitat fragmentation and may require a certain proportion of forest interior within their home ranges. Hargis et al. (1999) found that marten were nearly absent from landscapes having > 25% non-forest cover, even though forest connectivity was still present. Marten were sensitive not only to loss of habitat area, but also to the size and proximity of open areas (Hargis et al. 1999). However, forest edges may not always be detrimental to marten. Buskirk and Powell (1994) concluded that marten use of forest edges may depend on the vegetation composition and structure on either side. In California, marten preferred edges that bordered mesic meadows (Simon 1980, Spencer et al. 1983). In Maine, edge between residual conifer forests and regenerating clearcuts was used in proportion to availability (Chapin 1995, Chapin et al. 1998). Nevertheless, most of the literature and all of the wildlife experts we surveyed suggest that edges adversely affect marten habitat capability.
The size of marten home ranges is influenced by such factors as the abundance of food, population density, and the physiological condition of individual martens (Marshall 1951, Weckwerth and Hawley 1962, Soutiere 1979). Typically, male home ranges (200-1500 ha) are two to three times greater than female home ranges (80 - 840 ha) (Lofroth and Banci 1991). Adult martens tend to be solitary, somewhat territorial, and intrasexually tolerant in terms of sharing the same territories. Often adult male home ranges may overlap two to six adult female home ranges (Powell 1994, Clark 1984). The maximum density is 2 marten per km2 (Thompson and Colgan 1994). The marten's preferred prey is the red-backed vole (Clethrionomys spp.), which also occupies late-seral interior conifer forests (Nordyke and Buskirk 1991).
Effects of fire on marten habitat vary with size and severity of fire (Koehler and Hornocker 1977, Spencer et al. 1983, Koehler et al. 1990). Severe fire returns late-seral forest to early-seral conditions, which are not preferred by marten. Under natural conditions, however, a mosaic of early- and late-seral forests ensures that suitable marten habitat always exists somewhere in the landscape. Pine marten are a permanent resident in our study area, and are listed regionally as a sensitive species due to recent loss of habitat and apparent decline in their populations. We included the pine marten as a habitat specialist associated with late-successional high-elevation conifer forests, and expect populations to be sensitive to fluctuations in habitat availability caused by natural stand-replacing disturbances.
Three-toed Woodpecker
Three-toed woodpeckers are considered post-disturbance specialists; e.g., they have been found in high densities for a period of five to seven years following fire in conifer or aspen stands (Yaeger 1955, Harris 1982, Hitchcox 1988, Hutto 1995, Caton 1996, Hoffman 1997). The increase in woodpecker density is due to the increase in snag density and bark beetle (Dendricotonus spp.) populations (Koplin 1969, Taylor and Barmore 1980). Three-toed woodpeckers apparently feed almost exclusively on wood-boring insects, especially larvae and pupae of bark beetles (Goggans et al. 1989). In the absence of stand-replacing fires and bark beetle outbreaks, three-toed woodpeckers persist at low densities in late-seral spruce-fir, mixed-conifer and aspen forests where snags and older trees are present (Short 1974, Toone 1993, Villard 1994, Hutto 1995).
Three-toed woodpeckers are thought to have evolved circumboreally with spruce (Picea spp.) forests and seem to prefer these tree species over others in montane forests (Bock and Bock 1974). Furthermore, clumping of snags in small patches in forest stands seems to enhance habitat for this species (Thomas 1979). Both frequency and intensity of fire and bark beetle outbreaks influence habitat quality (Hoffman 1997).
Territories vary in response to prey availability; in late-seral forests territories range from 20-528 ha, and in extremely favorable conditions (e.g., recent burns or insect outbreaks) territories range from 0.5-5 ha (Towery 1984, Goggans et al 1989). Density varies as well, from one pair per 0.4 ha to one pair per 40 ha. Both sexes maintain breeding territories during winter, living either solitarily or in pairs (Hogstad 1970).
Recently disturbed areas with standing dead trees are beneficial to this species, and so we used three-toed woodpecker as an example of a species associated with transient post-disturbance habitats. Three-toed woodpeckers are regionally listed as a sensitive species due to population declines throughout the United States. Since three-toed woodpeckers specialize on conditions following fires and bark beetle outbreaks, we expect the availability of habitat to vary dramatically in response to fire and bark beetle disturbance and successional processes over time.
Olive-sided Flycatcher
Olive-sided flycatchers are neotropical migrants that select high-contrast edges between early- and late-seral conifer forests. As summarized by Altman (1997), their preferred breeding habitat typically occurs 1) within forest burns where snags and tall, residual live trees remain (Hutto 1995, Raphael et al. 1987, Kotliar and Melcher 1997); 2) near water along the wooded shores of streams, lakes, rivers, beaver (Cantor canadensis) ponds, bogs, and muskegs, often where snags are present (Gibson & McDonald 1975, Kessel and Gibson 1978; Godfrey 1986, Cheskey 1987, Kotliar and Melcher 1997); 3) at forest edges near openings in the forest, often at the juxtaposition of late- and early-seral forest (McGarigal and McComb 1995, Kotliar and Melcher 1997); and 4) in semi-open forest stands with a low percentage of canopy cover (Scott et al. 1982, Carey et al. 1991). Olive-sided flycatchers use open areas as foraging habitat and use "edges" of conifer stands next to open areas as nesting habitat (Altman 1997, Bent 1942). The presence of prominent trees or snags, which serve as foraging and singing perches, is a common feature of all nesting and foraging habitat. Finch and Reynolds (1988) reported that the species was more abundant along edges of spruce-fir forests than in aspen or mixed aspen-conifer forests in the central Rocky Mountains.
Olive-sided flycatchers are frequently reported as a species associated with burned-over forest (Raphael et al. 1987, Bock and Lynch 1970, Granholm 1982, Pfister 1980, Edwards 1973). It was one of 15 species more abundant in early post-fire communities than in any other major cover type in the Northern Rocky Mountains (Hutto 1995). This association is likely due to creation of forest openings and increased edge at the interface of burned and unburned forest, as well as an increase in populations of aerial insects (Hutto 1995).
Nesting territories are relatively large for a passerine bird, up to 40-45 ha per pair, but most often are in the range of 8-20 ha per pair (Altman 1997). Furthermore, limited banding data suggests strong site fidelity (Altman 1997). Nests generally are often placed no more than 50 m from the stand edge (pers. comm. Schultz). These flycatchers prey exclusively on flying insects, including bees, wasps, flying ants, beetles, moths and dragonflies (Bent 1942, Altman 1997). Current data indicates population declines in western North America due to habitat loss/alteration on wintering and breeding grounds. They are regionally listed as a sensitive species and occur within our study area. Since stand-replacing disturbances result in a mosaic of early and late-successional forests, we expect olive-sided flycatcher habitats to vary in response to natural disturbance processes.
Elk
Elk are a generalist species found in association with high-elevation conifer and aspen forests and subalpine meadows during the summer (Boyce and Hayden-Wing 1980). They prefer conifer and aspen forests as hiding cover, and use forest openings and subalpine meadows for foraging (Reynolds 1966, Thill et al. 1983). This large ungulate usually has distinct summer and winter ranges which are often reached by recognizable migration routes. Many researchers have reported the importance of mature conifer forests associated with poorly drained, cool, moist soils as important habitat components for cover during late summer (Edgerton and McConnell 1976, Pederson et al. 1980). Riparian areas, drainage heads, saddles, and wet meadows also contribute significantly to overall use of an area by elk (Christianson et al. 1993). Coniferous cover provides protection for calves from predators such as coyotes (Canis latrans) and bobcats (Lynx rufus) (Waldrip and Shaw 1980). Elk also use conifer stands as movement corridors (Brazda 1953, Bear 1989).
Size, location, and connectedness of cover and foraging areas are important considerations in elk habitat (Hillis et al. 1991). Data suggest that elk are less selective about vegetative characteristics of coniferous cover and more responsive to size and adjacency of habitat areas (Lyon and Canfield 1991). Specifically, they prefer both cover and foraging areas in close proximity. Results from many studies show decreased use of forage and cover habitat as the distance away from the cover-forage edge increases (Harper and Swanson 1970, Witmer 1981, Wilms 1971, Reynolds 1962, Thomas et al. 1979, Pederson et al.1980, Thomas and Toweill 1982, Leckenby 1984, Irwin and Peek 1983). Lyon (1976) reported heavier elk use in 5-20 ha openings when compared to larger openings. Reynolds (1962, 1966) reported that elk use of open areas for foraging decreases beyond 200 m from the edge of cover. Hershey and Leege (1982) reported that elk that are observed from the air in northern Idaho were usually within 150 m of cover. Witmer et al. (1985) found that the majority of elk use of foraging areas occurs within 100 m of the edge of cover and also that elk use of cover occurs within 300 m of the edge of forage. Furthermore, data suggest that elk prefer relatively level areas with less than 40% slope (Scott 1978, Lehmkukl 1981, Unsworth et al. 1998). Prefered sites for calving areas are on slopes of less than 15% with adequate hiding cover and forage nearby, and water should be available within 3,000 m of the calving site. Where the topography is steep, calving areas are usually situated on benches (Hershey and Leege 1982).
Data on home range sizes indicate a large variation among individuals of all ages and sexes (Bear 1989, Craighead et al.1973). Craighead et al. (1973) found that home ranges varied from 160 hectares to 3110 hectares (Bear 1989, Craighead et al.1973). Waldrip and Shaw (1980) found that cow home ranges varied from 619 hectares to 930 hectares.
Stand-replacing disturbances may cause an increase in habitat quality for foraging while also causing a decrease in habitat quality for hiding cover (Lyon and Basille 1979). Elk are a common species in the Rocky Mountains and have a large population within our study area. Since we incorporated elk as a generalist species, we did not expect a high degree of variation in the amount and configuration of capable habitat from disturbances over time.
HABIT@ Capability Models
Click on the links below for each species’ HABIT@ model. Note, a complete understanding of HABIT@ (see HABIT@ - Model Overview) is prerequisite to understanding these model descriptions.
*Note, the following links point to Microsoft Word Documents.