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U.S. Forest Service
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United States Department of Agriculture

What is FVS?

The Forest Vegetation Simulator (FVS) is a family of forest growth simulation models. It is a system of highly integrated analytical tools that is based upon a body of scientific knowledge developed from decades of natural resources research and experience. Since the development of the first model for northern Idaho in 1973, FVS has evolved into a collection of “variants” which represent different geographic areas across the country.

FVS answers questions about how forest vegetation will change in response to natural succession, disturbances, and proposed management actions. Extensions to the base model are available to assess the effects of insects, disease, and fire. The Fire & Fuels Extension (FFE) includes live tree, dead tree, down dead wood and forest floor biomass information, which can be used to estimate changes in carbon stocks over time.

A climate-sensitive version known as Climate-FVS is currently available for western states, and an eastern version is in development. Climate-FVS changes core growth, mortality, and regeneration estimates to respond to climate change, according a user-selected general circulation model (GCM), thereby allowing users to model the effects of management under changing climate conditions.


The Forest Vegetation Simulator (FVS) is an individual-tree, distance-independent, growth and yield model (Dixon 2002). It has been calibrated for specific geographic areas (variants) of the United States (Figure 1). FVS can simulate a wide range of silvicultural treatments for most major forest tree species, forest types, and stand conditions.

Map of the United States with an inset map of the west coast of Canada and southern Alaska showing the FVS Variant locations.

The original Prognosis model (Stage 1973) was developed for northern Idaho and western Montana. The Prognosis model framework was retained as data from other geographic areas was analyzed to develop new model variants. In the early 1980s, Prognosis became the Forest Vegetation Simulator (FVS) and was adopted by the USDA Forest Service National Forest System as the national standard for forest growth and yield modeling.

The FVS Staff of the Forest Management Service Center (FMSC) in Fort Collins, Colorado, maintains, supports, develops, and provides training for FVS. The FMSC performs a technology transfer role, working with researchers and National Forest staff from various geographical areas to incorporate their findings into the FVS framework. The FMSC is constantly upgrading existing variants and developing additional variants.

FVS Models and Components

The FVS software system is comprised of the regional FVS variants, model extensions, a graphical user interface (called Suppose), and a suite of post-processing programs that allow stand visualization and customize output reports to meet user requests.

FVS Geographic Variants

An FVS variant is a growth and mortality model calibrated to a specific geographic area of the United States. There are 20 different FVS variants. Users select an appropriate FVS variant for their area. FVS variants are calibrated for each of the major tree species within a geographic region. Extensions to the base variants are also available to assess the effects of insect, disease, and fire.

You can find information regarding the codes, relationships, and logic specific to the individual variants in the Variant Overview documents. We developed an FVS Variant Map to suggest the FVS variant for any point in the United States, and is distributed in the form of a shapefile.

Model Extensions

Extensions to FVS are models that function interactively with the base FVS geographic variant to simulate the effects of various forest ecological disturbances on forest growth and mortality.

Insect and Disease Extensions

The insect and disease extensions incorporate the effects of insects and forest pathogens on forest stands. Fully functioning physiologic sub-models include:

  • Western root disease model
  • Douglas-fir Beetle Model
  • Douglas-fir Tussock Moth Model
  • Dwarf Mistletoe Model
  • Lodgepole Mountain Pine Beetle Model
  • Western Spruce Budworm Damage Model
  • White Pine Blilster Rust Model
  • Westwide Pine Beetle Model 

Fire and Fuels Extension (FFE)

The FFE links the FVS variant with models of fire behavior, fire effects, fuel loading, and snag dynamics. Model outputs include predictions of potential fire behavior and effects and estimates of snag levels and fuel loading over time.

Carbon Submodel

The FVS carbon reports are part of the Fire and Fuels Extension to FVS and estimate the amount of carbon stored in various forest stand components, such as standing live and dead trees and surface fuels, over time.


The Climate Extension to the Forest Vegetation Simulator (Climate-FVS) provides forest managers a tool for considering the effects of climate change on forested ecosystems.


The Economic Extension (ECON) computes economic measures during FVS simulations to aid evaluation of silvicultural alternatives.

Suppose User Interface

Suppose is the graphical user interface for the FVS software. It permits entry of proposed management plans or policies into the FVS system using specific FVS keywords or using standard forest management terminology

Post Processing FVS Output

Examples of FVS Post-Processor outputs: reports, graphs, and SVS.

Post processors are stand-alone applications that manipulate FVS output information. They extend FVS's capabilities performing additional computations, producing additional reports, providing graphical display, and simulated stand images. Examples of FVS post-processors include Bark Beetle Risk Calculations, calibration summary statistics, stand and stocking tables, Multistory Elk Hiding Cover, and Spectrum Export Tables.

FVS Steering Team

An FVS Steering Team monitors and guides requests for system refinement. The fifteen member FVS Steering Team includes a mix of Forest Service field and research personnel, other agencies, and various other personnel with the purpose of providing strategic guidance to the FVS group in development, enhancement, and application of the model using best available science.

FVS Validation

In the spring of 2008, the Validation Subcommittee of the FVS Steering Team established protocols for variant testing and validation. The FVS Validation page contains the validation protocols document along with validation results and related documents.