Use of Permanent Forest Inventory Data to Determine Trends in Forest Growth and Their Relationship to Climate and Soil Sensitivity to Acid Deposition : Monitoring Air Pollution Impact on Permanent Sample Plots, Data Processing and Results Interpretation

1991

S. 78-83

2 Abb., 3 Tab., 4 Lit.

Unselbständiges Werk

200059917

Since 1987, TVA has been involved in a study to evaluate current forest growth trends and their relationship to naturally occurring stresses and atmospheric pollution. The study is based on an extensive historical database of permantent forest inventory information supplemented with comprehensive site descriptions, detailed disturbance histories, sitespecific soil series description, and tree-ring analysis. Three study sites were selected to represent the forest of the region based on availability of historical data from the permanent plot system and physiographic location. A total of 207 permanent plots were selected from these study sites for reinventory and collection of additional data based on species composition, sizes of trees on the plot, and absence of significant recent distrubance. Unfortunately, corresponding air pollution data are not available for comparison with observed growth trends. Therefore, our approach 1)to identify possible changes in sensitivity to other known environmental stresses that might be associated with a change in tree or forest vigor and 2) to stratify plots by hypothesized soil sensitivity to acidification and evaluate changes in growth relative to these classifications. Repeated measures analysis was used with the plot inventory data to identify changes between stand growth and site factors. A time-variant response function, the Kalman filter, was used with annual tree increment series to identify ttends in tree sensitivity to climate, results of the analyses of plot data indicated that within a forest stand, the influence of site factors on growth cecame less important over time, and that differences in growth attributable to soil sensitivity to acidification were not significant. Tree-ring analysis indicated that in general, individual trees became less sensitive to climatic extremes over time. However, a recent change in this trend was observed in the majority of series. This may indicate an undefined change in weather patterns, or a change in sensitivity to climate caused by an additional environmental stress.