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.