LANDFIRE Rapid Assessment Reference Condition Model: Black sage

The Rapid Assessment (RA) vegetation dynamics data help to synthesize the best available knowledge of vegetation dynamics and quantify the natural range of variability in vegetation composition and structure.  Models consist of two components: (1) a comprehensive description and (2) a quantitative, state-and-transition (box) model, created in the public domain software VDDT (Vegetation Dynamics Development Tool; Beukema et al. 2003).

RA vegetation models were based on a simple, standardized five-box model that combines three generic succession stages with two canopy cover classes. Each class is specifically defined for individual models. Variations on this standardized model were also developed.  Models were developed in 2004-2005 during workshops across the conterminous United States where regional vegetation and fire ecology experts synthesized the best available data on vegetation dynamics and disturbances for vegetation communities in their region. A peer review process following workshops garnered additional expert input and offered an opportunity to refine models.

Quantitative models are based on inputs such as fire frequency and severity, the probability of other disturbances, and the rate of vegetation growth. Inputs are derived from literature review and expert input during and after modeling workshops. Models simulate several centuries of vegetation dynamics and produce outputs such as the percent of the landscape in each class and the frequency of disturbances. Outputs are checked against available data whenever possible, and are peer-reviewed during and after expert workshops.

Model descriptions and quantitative outputs were used in the RA to help define and map potential natural vegetation groups, or the vegetation communities that are likely to exist under the natural range of variability in biophysical environments and ecological processes, including fire and other disturbances. Models are used as reference conditions to calculate Fire Regime Condition Class (FRCC), a standardized, interagency index to measure the departure of current conditions from reference conditions (Hann et al 2004).  For a complete description of the methodology used to develop RA vegetation models, please consult the “LANDFIRE Rapid Assessment Modeling Manual” (The Nature Conservancy et al. 2005).