Assessing Forest Health Conditions in Idaho with Forest Inventory Data

Abstract

Periodic inventory measurements of forest characteristics published by the U.S. Forest Service are used to assess trends in forest conditions in Idaho. Forest species composition, measured by growing stock volume, has changed since 1952. Western white pine and ponderosa pine have declined by 60% and 40%, respectively. True firs (mostly grand fir) increased by 60% lodgepole pine by almost 40%, and Douglas-fir, the predominant species throughout the state, increased by 15%. Measurements of tree mortality across the state and region from 1952 to 1987 establish a baseline regional range for judging current conditions. Recent mortality data from some Idaho national forests are much higher than the upper limit of the baseline regional range. On the Boise and Payette National Forests in southwestern Idaho, annual mortality exceeds annual growth. Recent inventories of national forests in northern Idaho show mature stands have mortality well above the baseline regional range, which projects into a negative net gro...