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Abstract

Understanding historical ecosystem diversity and wildlife habitat quality can provide a useful reference for managing and restoring rangeland ecosystems. We characterized historical ecosystem diversity using available empirical data, expert opinion, and the spatially explicit vegetation dynamics model SIMPPLLE (SIMulating Vegetative Patterns and Processes at Landscape ScaLEs) for a landscape of approximately 946,000 ac in eastern Wyoming. We used SIMPPLLE to simulate plant community dynamics as a result of historical disturbance events (for example, fire, bison grazing, and prairie dog activity), climate, and landscape elements (for example, ecological site, proximity to water, and elevation) and their interactions to derive estimates of the historical range of variability for each grass/shrub ecosystem. For each NRCS designated ecological site we defined the historical states that occurred in the presence of grazing by native herbivores and fire, and identified the processes for movements among states within each site. For each historically occurring state within the delineated landscape we determined the mean ac it occupied and the range of variability (in other words, minimum and maximum ac a state occupied). Comparisons of historical grass/shrub ecosystem diversity of the area with existing conditions indicate that there have been significant changes, most notably the lack of representation of ecosystems dominated by grass species that typically decrease with grazing, the widespread presence of introduced species especially annual brome, and alterations to fire regimes. Through comparisons of historical ecosystem diversity with existing conditions, we identified specific plant communities that are underrepresented and in need of restoration to maintain ecosystem diversity and wildlife habitat.

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