The Western Root Disease Model Version 3.0, an extension to the Forest Vegetation Simulator (FVS), simulates the increased mortality and reduced growth effects of four root diseases on 40 tree species. The root diseases represented are: P- and S-type annosus, armillaria, and Phellinus weirii (laminated root rot); the tree species represented in any given FVS variant are dependant on the tree species list for that specific variant. trees whose health and vigor have been compromised by root disease lend themselves to successful bark beetle attacks and windthrow; therefore, the ability to simulate four functional bark beetles types and windthrow is also provided in the model.
A simplified explanation of how the model functions involves four basic concepts: 1) root disease centers, 2) expansion of those centers, 3) infection of trees within centers, and 4) the progression (intensification) of the disease through a tree's root system. As root disease intensifies in a tree, the tree's growth potential is increasingly diminished until the level of infection in the root system kills the tree.
The model is highly parameterized, and the user has access to alter many of those parameters through keywords. Initialization of the model requires at least the specification of root disease type via a keyword, and the model can be directed to interpret or ignore root disease damage codes that may exist in the FVS input tree data. Direct root disease management options available are stump removal and the application of borate.
The Western Root Disease Model Version 3.0 was developed by a team of professionals from the USDA Forest Service and ESSA Technologies Ltd of Vancouver, B.C., with the completion of development occurring in 1996 and the placement of the model into production by the Forest Health Technology Enterprise Team . in 1997. The Western Root Disease Model is available as an extension to most western FVS variants.