Forest Health in North America: Some Perspectives on Actual and Potential Roles of Climate and Air Pollution

Abstract

The perceived health of forest ecosystems over large temporal and spatial scales can be strongly influenced by the frames of reference chosen to evaluate both forest condition and the functional integrity of sustaining forest processes. North American forests are diverse in range, species composition, past disturbance history, and current management practices. Therefor the implications of changes in environmental stress from atmospheric pollution and/or global climate change on health of these forests will vary widely across the landscape. Forest health surveys that focus on the average forest condition may do a credible job of representing the near-term trends in economic value while failing to detect fundamental changes in the processes by which these values are sustained over the longer term indications of increased levels of environmental stress on foreat growth and nutrient cycles are currently apparent in several forest types in North America Measurements of forest ecophysiological responses to air pollutants in integrated case studies with four forest types (southern pine, western pine, high elevation red spruce, and northeastern hardwoods) indicate that ambient levels of ozone and/or acidic deposition can alter basic processes of water, carbon, and nutrient allocatipn by forest trees. These changes then provide a mechanistic basin for pollutant stress to enhance a wider range of natural stresses that also affect and are affected by these resources. Future climatic changes may ameliorate (+CO₂ or exacerbate (+ temperature, + UV-B) them effects. Current projections of forest responses to global climate change do not consider important physiological changes induced by air pollutants that may amplify climatic stresses. These include reduced rooting mass, depth, and function, increased respiration, and reduced water use effiency. Monitoring and understanding the relative roles of natural and anthropogenic stress in influencing future forest health will require programs that are structured to evaluate reaponses at appropriate Bequencia across gradients in both forest resources and the stresses that influence them such programs must also be accompanied by supplemental process-oriented and pattern-oriented investigations that more thoroughly test cause and effect relationships among stresses and responses of both forests and the biogeochemical cycles that sustain them.

Citation

McLaughlin, S.; Percy, K. 1999. Forest Health in North America: Some Perspectives on Actual and Potential Roles of Climate and Air Pollution. Water, Air, and Soil Pollution 116: 151-197, 1999.