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).