Using Forest Inventory Data to Assess Aspen Health in the Western United States

The health of the regional aspen (Populus tremuloides Michx.) community is currently a disputed topic in the Interior West. Numerous recent studies have addressed “aspen decline,” purportedly a regional phenomenon, using landscape-level analyses. While we assume that aspen conditions vary throughout the Interior West we believe a study of a regional forest health issue should employ a systematic plot network as a complement to local empirical studies. The study has four primary objectives: 1) Conduct an empirical assessment of aspen conditions across Utah using FIA (USDA Forest Service’s Forest Inventory and Analysis) annual inventory data; 2) Refine and enhance statistical methods employed in previous studies for potential export to other regional aspen assessments; 3) Assess the utility of extensive data sets in addressing large-scale forest health issues; 4) Place the Utah example in the context of the greater western U.S. aspen community.

In the Rocky Mountains “healthy” or “stable” aspen communities are regenerating vegetatively at relatively short time intervals (20-80 years) via disturbances such as fire, wind, avalanche, or management actions. Forest assessments from examination of FIA stand structure and condition variables (species, crown position, dbh, stand age, regeneration, tree damage, and recent disturbance) at a single point in time provide a ‘window on the past’ as to whether aspen is actively sustaining itself or declining. Variables that prove to have significant relations with NMDS (Nonmetric Multidimensional Scaling) ordinations of stand structure and composition will be combined into a synthetic aspen stability index through multivariate statistical analysis. Results presented here quantify the extent of aspen stability, and hence provide a current assessment of aspen community health in Utah.