Western Root Disease Model

The Western Root Disease Model (WRDM) extension to FVS/Prognosis is a non-spatial model that simulates the impacts of Armillaria mellea, Phellinus weiri, and S- and P-type Annosus on the growth and mortality of trees in a stand. Stand and disease management options, such as clear cuts, partial cutting, planting, stumping, or borax application can affect the spread of the infection.

The model simulates the spread of disease patches (“centers”) within the stand. New infections occur between trees within patches or as the center spreads into uninfected areas. Once a tree is infected, the disease spreads through its root system, spreading more slowly in larger trees. As the disease spreads, growth slows and the tree ultimately dies. Each tree species reacts differently to infection; some species, such as Douglas-fir, are highly susceptible while others are immune. Thus, the impact of the disease in the stand is highly dependent on the species composition of the stand as well as the size and density of the trees.

The initial root disease conditions in the stand are set by the user based on tree inventory damage codes, estimates of the density of infected and uninfected trees, and information about root disease centres present in the stand. The user also has access to a number of parameters which describe, among other options, the relative susceptibility of different tree species to the root disease, and the rate of progress of the disease in the tree.

Because stands that contain root disease are often more susceptible to bark beetles or windthrow, the model also includes the ability to simulate these events with user-defined parameters. Since different species of bark beetles may attack the stands, four functionally different bark beetle types are available, and the user is thus able to create a wide range of different infestations.

This model was created by ESSA in cooperation with the USDA Forest Service and the BC Ministry of Forests. It is linked to most of the US western variants of FVS, and to Prognosis^BC.

Case study: Partial Harvesting in the Nelson Forest Region, British Columbia

Additional Information at Related Sites:
USDA Forest Service Western Root Disease Model site
Prognosis^BC web site - Extensions to Prognosis^BC, Western Root Disease Extension

Western Root Disease Model Reports and Publications