Measuring effects of air pollution stress on forest productivity: perspectives, problems, and approaches

Changing levels and patterns of emissions of atmospheric pollutants in recent decades have resulted in increased exposure of extensive forests in Europe and North America to both gaseous pollutants and acid rain. Reports of decreased growth and increased mortality of forest trees in areas receiving high rates of deposition of atmospheric pollutants have emphasized the need to better understand and quantify both the mechanisms and kinetics of potential changes in forest productivity. The complex chemical nature of combined pollutant exposures and the fact that these changes may involve both direct effects to vegetation as well as indirect and possibly beneficial effects mediated by a wide variety of soil processes make quantification of such effects particularly challenging. A variety of productivity studies in Europe and the US have been evaluated. Dendroecological approaches, which combine detailed analysis of long-term growth trends as influenced by tree age, competitive status, climatic variables, and pollutant levels, offer great promise for quantifying both the temporal and spatial relationships of productivity changes and their relationship to patterns of deposition of atmospheric pollutants. Subsequent research to delineate mechanisms of effects and simulate the long-term integrative effects of altered tree growth and soil nutrient dynamics will be required tomore » provide a strong scientific basis for establishing cause-and-effect relationships between air pollution and changes in forest productivity. 42 references.« less