Development of Potential Vegetation Model to Assess Threats to Forest Health

T. M. Rice, J. E. Stewart, M.-S. Kim, and G. I. McDonald

USDA Forest Service Rocky Mountain Research Station

Habitat typing of forest stands provides a functional basis for development of tools to assess landscape-level potential threats to forest health. Habitat types (associations of plant species) are well-accepted indicators of general site conditions such as temperature and moisture; however, traditional assignment of habitat types at the landscape level lacks the resolution to discover important process-level parameters requisite to effectively assess diverse environmental threats posed by disease, insect attack, invasive weeds, fire and global climate change. While these threats tend to function across a wide range of plant communities, their behaviors differ within narrower ranges of site conditions influenced by interactions of topography, soil, temperature and precipitation patterns, as well as past disturbance and management practices. Environmental variations occurring within sites must be recognized and used along with broader-scale characteristics to create appropriate management strategies specific to the threat being addressed. For example, data from numerous sites throughout the western United States show that distribution and activity of Armillaria ostoyae, a causal agent of Armillaria root disease, is strongly correlated with plant communities defined by soil temperature-moisture regimes.

Geographic Information System (GIS) tools provided the ability to design an unbiased plant community classification system from terrain and climate analyses of a forested area in Montana, USA. GIS layers produced from stand maps and elevation and weather models were combined to more precisely predict landscape-scale hazard potential and help delineate appropriate management units for assessment of Armillaria threat. New plant community boundaries were drafted based on modeled soil temperature-moisture regimes and compared to traditionally defined stands, revealing significant variability within some stands. Capturing site variability was important in accurately assessing potential presence of pathogenic Armillaria species. Continued development and validation using issue-appropriate data should prove this approach useful for assessing diverse abiotic and biotic threats to forest health, even in the face of changing climate and continued disturbance.

corresponding author:

T.M. Rice
USDA Forest Service
Rocky Mountain Research Station
1221 S. Main Street
Moscow, ID 83843
208-883-2308
trice@fs.fed.us