Responses of Northern U.S. Forests to Environmental Change

In the Global Change Research Act of 1990, "global change" is defined as "changes in the global environment (including alterations in climate, land productivity, oceans or other water resources, atmospheric chemistry, and ecological systems) that may alter the capacity of the Earth to sustain life. " For the purposes of this book, we interpret the definition of global change broadly to include physical and chemical environmental changes that are likely to affect the productivity and health of forest ecosystems over the long term. Important environmental changes in the Northern United States include steadily increasing atmospheric carbon dioxide, tropospheric ozone, wet and dry deposition of nitrogen and sulfur compounds, acidic precipitation and clouds, and climate variability. These environmental factors interact in complex ways to affect plant physiological functions and soil processes in the context of forest landscapes derived from centuries of intensive land use and natural disturbances. Research in the North has begun to unravel some key questions about how environmental changes will impact the productivity and health of forest ecosystems, species distributions and abundance, and associations of people and forests. Initial research sponsored by the USDA Forest Service under the United States Global Change Research Program (USGCRP) was focused on basic process-level understanding of tree species and forest v VI Preface ecosystem responses to environmental stress. Chemical pollution stresses received equal emphasis with climate change concerns.

This volume presents five years of research in the Northeastern and North Central United States by the U.S. Department of Agriculture Forest Service's Northern Global Change Program. This longterm research contributes to our understanding of the effects of multiples stresses on forest ecosystems over multiple spatial and temporal scales. The book provides sound ecological information for policy makers and land-use planners as well as for researchers in ecology, forestry, atmospheric science, soil science and biogeochemistry.

Section 1. An Introduction to Northern U.S. Forest Ecosystems.- 1. Forest Resources and Conditions.- 2. Geologic and Edaphic Factors Influencing Susceptibility of Forest Soils to Environmental Change.- 3. Climate and Atmospheric Deposition Patterns and Trends.- 4. Forest Declines in Response to Environmental Change.- Section 2. Global Change Impacts on Tree Physiology.- 5. Interacting Effects of Multiple Stresses on Growth and Physiological Processes in Northern Forest Trees.- 6. Physiological and Environmental Causes of Freezing Injury in Red Spruce.- 7. Tree Health and Physiology in a Changing Environment.- 8. Atmospheric Deposition Effects on Surface Waters, Soils, and Forest Productivity.- Section 3. Ecosystem-Scale Interactions with Global Change.- 9. Nitrogen Saturation in Experimental Forested Watersheds.- 10. Effects of Soil Warming on Carbon and Nitrogen Cycling.- 11. Regional Impacts of Climate Change and Elevated Carbon Dioxide on Forest Productivity.- 12. Regional Impacts of Ozone on Forest Productivity.- 13. Effects of Climate Change on Forest Insect and Disease Outbreaks.- 14. Forest Responses to Changing Climate: Lessons from the Past and Uncertainty for the Future.- Section 4. Summary.- 15. Summary of Prospective Global Change Impacts on Northern U.S. Forest Ecosystems.