Research Abstract.--Under the paradigm of ecosystem management, there is widespread recognition of the need to better understand the interplay between process and pattern in ecosystems and landscapes. There is growing interest in understanding how these processes and patterns change ecosystems and landscapes over time, and whether human activities have caused ecosystems or landscapes to move outside their expected range of variation. To establish the expected range of variation under a natural fire disturbance regime, we developed a spatially explicit dynamic landscape simulation model (RMLANDS). The simulation model provides control over various details of the fire disturbance regime such as the fire frequency, fire size distribution, and rotation period.

I applied this simulation model to a representative area of high-elevation forests in Southwestern Colorado on the Pagosa District of the San Juan National Forest. The purpose of the simulations was:

1. To quantify the expected range of variation in landscape structure under the current climate disturbance regime, as representative of pre-settlement conditions;
2. to characterize the relationship between landscape extent and the expected range of variation in landscape structure; and
3. Tto determine the sensitivity in landscape structure dynamics to variation of fire frequency, size, and rotation period.

I quantified the variation in landscape structure dynamics using FRAGSTATS. The results indicate that (1) under the current climate disturbance regime, the range of variability for all metrics was surprisingly small; (2) temporal variability in landscape structure increased nonlinearly as the spatial extent of the landscape decreased; and (3) landscape structure dynamics were most sensitive to changes in rotation period, where decreasing fire frequency increased the range of variability in landscape structure metrics, and changes in maximum fire size shifted the landscape into a new equilibrial condition. The results of this study provide a framework for comparison with subsequent simulations of anthropogenic disturbance regimes.