BLM REA COP 2010 Inter-Mountain Basins Big Sagebrush Shrubland (LANDFIRE BpS): Change Agents and Disturbance Types

This dataset shows historic change agents and disturbance types within the historic distribution of this vegetation community as mapped in the LANDFIRE Biophysical Settings (BpS v1.0) dataset. The BpS provides an estimate of the distribution of this community under pre- Euroamerican settlement reference conditions (including historic fire regimes). While based on biophysical gradients and limited training plot data, with resultant inaccuracies of prediction, the BpS provides the best available estimate of the distribution of this vegetation community. Existing vegetation classifications are inadequate for estimating the distribution of this community for the purposes of this analysis, because they only provide a single, recent snapshot in time of vegetation conditions that are often variable over time (i.e., a recently burned area may be classified as low cover herbaceous in the existing vegetation, but occupying a site that over long periods of time is occupied by shrubland). Change agents are those factors that have converted this vegetation into another state, such as conversion to urban areas. These were extracted from the LANDFIRE EVT, NLCD Impervious Surfaces, BLM GTLF (roads), current predicted invasive vegetation dataset (produced for this REA), and LANDFIRE Succession Class dataset to express the following change agent types: development, agriculture, invasive vegetation, and uncharacteristic native vegetation. Disturbances are those factors that have occurred within this system in recent years, that may have modified the vegetation community composition, structure, and dynamics. These disturbances may be part of the natural disturbance regime and thus beneficial for the ecological dynamics of a site, or they may be uncharacteristic due to increases of fire frequency (in arid shrublands), fuel buildup due to legacy effects of fire suppression, or presence of invasive vegetation. These disturbances were extracted from USGS fire perimeters (2000-2010), LANDFIRE Disturbance datasets (1999-2008), and BLM Pinyon-Juniper treatments. Caution should be exercised in interpreting this dataset. The BpS provides one possible estimate of the historic distribution of this vegetation community, but may contain inherent inaccuracies and biases (and thus over- or under-represent the distribution of this community). The change agents are based on measures of existing vegetation and landscape condition, and may not contain all factors that have affected this vegetation community. In particular, long-term conversion to other vegetation communities was not addressed in this analysis (overlays of BpS and existing vegetation datasets generally do not indicate long-term versus short-term vegetation conversions). Not all disturbances that affect this community may have been detected in the available datasets used to estimate disturbance. Overall, this dataset should be taken to provide one estimate of the net changes that have affected this vegetation community historically and recently.