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.
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 Manuala.
[Summary provided by The Nature Conservancy.]