Estimating Extent of Mortality Associated with the Douglas-Fir Beetle in the Central and Northern Rockies

Data collected from Douglas-fir stands infected by the Douglas-fir beetle in Wyoming, Montana, Idaho, and Utah, were used to develop models to estimate amount of mortality in terms of basal area killed. Models were built using stepwise linear regression and regression tree approaches. Linear regression models using initial Douglas-fir basal area were built for all study sites but produce low precision estimates. Regression tree models using initial Douglas-fir basal area of stand density index or both were also build for all sites. Regression tree models provide a more realistic approach to estimate potential mortality by creating more homogenous mortality classes with reduced variance. The models developed provide land managers with a basis for determining the potential mortality should a Douglas-fir beetle outbreak develop

Biological Evaluation of Tree Survivorship within the Lowman Fire Boundary, 1989-1993

In 1989, the Lowman fire burned 47,600 acres in the South Fork Payette River drainage near the town of Lowman, Idaho. Impact plots were installed to monitor tree survivorship and causes of mortality. Eighty two percent of the ponderosa pine and 52 percent of the Douglas-fir monitored in this study survived the fire. Trees which died from fire had an average crown scorch of 74 percent and trees which died from beetles had an average crown scorch of 48 percent. The data set compiled during this study was used to validate a probability of mortality equation developed by Reinhardt and Ryan (1988). This equation accurately classified trees as dead or alive 83 percent of the time. Marking guidelines for both Douglas-fir and ponderosa pine based upon DBH and percentage of the crown volume scorched could be developed using this equation