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

Abstract

Abstract. The perceived health of forest ecvqems over large temporal and spatial scalm can be strengly inlluenced by the frames of refmence chosen to e+aluate both forest condition and the timctional integrity of sustaining forsl processes. North American forests arc diverse in range, species compceiti~ past disturbance history, and current managementpracticcs.~~eforcthcimplikltionsofchangesinenvLonmentalstessGan~h~cpollution~or global climate change on health ofthese for&s will vary widely acrom the la&cape. Forest health surveys that fon the average forest condition may do a credible job of representing the near -term trends in economic value while failing to detect tin&mental changes in the processes by which thcae values are sustained over the longer term Indications of increased levels of environm mtal stress on foreat growth and nutrient cycles are currently apparent in several forest types in North America Measurements offorest ecophysiological responses to air pollutants in imegmud 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 ofnatural stresses that also a&d and are a&&d by these resources. Future clin+c changes may ameliorate (+ COJ or exacerbate (+ temperature, + W-B) them effects. Current projections of forest responses to global cliite change do not consider important physiological changes induced by air pollutanta that may amplitj climatic streasos. These include reduced rooting mass, depth, and function, increased respiration, and reduced water uee effkiency. Monitoring and understanding the relative roles of natural and anthropogenic stress in intluencing future forest health will requLs programs that are structured to evaluate reaponaea at appropriate Bequencia across gradients in both forest resourcea and the stresses that intlumce them Such programs must also be accompanied by supplemental pr--oriented and pattern -oriented investigations that more thoroughly test cause and effect relationships among str-and responses of both forests and the biogeochemical cycles that sustain them.

Community and population dynamics of spruce–fir forests on Whiteface Mountain, New York: recent trends, 1985–2000

“…We also did not find any evidence of collateral damage to balsam fir or paper birch in the wake of widespread spruce mortality (Perkins et al 1992;McLaughlin and Percy 1999). However, there were important changes in the rate and nature of biomass accumulation since the mid-1980s.…”

New exposure-based metric approach for evaluating O3 risk to North American aspen forests

“…In a comprehensive retrospective review of the roles of air pollutants and climate in North American forest health, McLaughlin and Percy (1999) reported that O 3 was deleteriously affecting forest ecosystem function across large and geographically widely separated areas of the continent. When considering relevance of this current research within the ambient exposure-based metric context (Foley et al, 2003), it is important to note that the growing season 4th highest daily max.…”

“…Since the late 1950s, an extensive scientific literature has been built on the O 3 impacts on forest trees (see reviews by Kickert and Krupa, 1990;Chappelka and Samuelson, 1998;McLaughlin and Percy, 1999;Percy, 2002;Percy et al, 2003;Andersen, 2003;Ashmore, 2004;Karnosky et al, in press), forest ecosystems (Miller and McBride, 1999;Bytnerowicz et al, 2003) and physiologically based modeling of North American forest response. Ollinger et al (1997) simulated the effects of O 3 on hardwood forest types in the northeastern US and estimated growth reductions between 3% and 22%.…”

Climate Change Projections for the United States Midwest

“…Enhanced carbon fixation during non-stressed periods, driven by the fertilization effect of elevated CO 2 , may compensate for reduced availability of soil moisture (Hanson and Weltzin 2000). However, changes in ambient levels of ozone and/or acidic deposition can alter basic processes of water, carbon, and nutrient allocation by trees (McLaughlin and Percy 1999). Increased nitrogen levels in the atmosphere may also promote plant growth, but could potentially pollute water resources (Johnson et al 2000).…”