United States Department of Effects of Climatic Variability and Agriculture Forest Service Change on Forest Ecosystems: Pacific Northwest Research Station A Comprehensive Science General Technical Synthesis for the U.S. Forest Report PNW-GTR-870 Sector December 2012 D E E P R A U R T LT MENT OF AGRICU The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of multiple use management of the Nation’s forest resources for sustained yields of wood, water, forage, wildlife, and recreation. Through forestry research, coop- eration with the States and private forest owners, and management of the national forests and national grasslands, it strives— as directed by Congress—to provide increasingly greater service to a growing Nation. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, sexual orientation, marital status, family status, status as a parent (in education and training programs and activities), because all or part of an individual’s income is derived from any public assistance pro- gram, or retaliation. (Not all prohibited bases apply to all programs or activities). If you require this information in alternative format (Braille, large print, audiotape, etc.), contact the USDA’s TARGET Center at (202) 720-2600 (Voice or TDD). If you require information about this program, activity, or facility in a language other than English, contact the agency office re- sponsible for the program or activity, or any USDA office. To file a complaint alleging discrimination, write USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call toll free, (866) 632-9992 (Voice). TDD users can contact USDA through local relay or the Federal relay at (800) 877-8339 (TDD) or (866) 377-8642 (relay voice users). You may use USDA Program Discrimination Complaint Forms AD-3027 or AD-3027s (Spanish) which can be found at: http://www.ascr.usda.gov/complaint_filing_cust.html or upon request from a local Forest Service office. USDA is an equal opportunity provider and employer. Editors James M. Vose is a research ecologist, U.S. Department of Agriculture, Forest Service, Southern Research Station, Center for Integrated Forest Science and Synthesis at North Carolina State University, Department of Forestry and Environmental Resources, Campus Box 8008, Raleigh, NC 27695; David L. Peterson is a research biological scientist, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, Pacific Wildland Fire Sciences Laboratory, 400 N 34th Street, Suite 201, Seattle, WA 98103; Toral Patel-Weynand is a national coordinator for bioclimatology, U.S. Department of Agriculture, Forest Service, Research and Development, 1601 N Kent Street, RPC 4, Arlington, VA 22209. Effects of Climatic Variability and Change on Forest Ecosystems: A Comprehensive Science Synthesis for the U.S. Forest Sector Effects of Climatic Variability and Change on Forest Ecosystems: A Comprehensive Science Synthesis for the U.S. Forest Sector James M. Vose, David L. Peterson, and Toral Patel-Weynand, Editors Published by: U.S. Department of Agriculture Pacific Northwest Research Station Forest Service Portland, Oregon General Technical Report PNW-GTR-870 December 2012 i GENERAL TECHNICAL REPORT PNW-GTR-870 Abstract Vose, James M.; Peterson, David L.; Patel-Weynand, Toral, eds. 2012. Effects of climatic variability and change on forest ecosystems: a comprehensive science synthesis for the U.S. forest sector. Gen. Tech. Rep. PNW-GTR-870. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 265 p. This report is a scientific assessment of the current condition and likely future condition of forest resources in the United States relative to climatic variability and change. It serves as the U.S. Forest Service forest sector technical report for the National Climate Assessment and includes descriptions of key regional issues and examples of a risk-based framework for as- sessing climate-change effects. By the end of the 21st century, forest ecosystems in the United States will differ from those of today as a result of chang- ing climate. Although increases in temperature, changes in precipitation, higher atmospheric concentrations of carbon dioxide (CO2), and higher nitrogen (N) deposition may change ecosystem structure and function, the most rapidly visible and most significant short-term effects on forest ecosystems will be caused by altered disturbance regimes. For example, wildfires, insect infestations, pulses of erosion and flooding, and drought-induced tree mortality are all expected to increase during the 21st century. These direct and indirect climate-change effects are likely to cause losses of ecosystem services in some areas, but may also improve and expand ecosystem services in others. Some areas may be particularly vulnerable because current infrastructure and resource production are based on past climate and steady-state conditions. The ability of communities with resource-based economies to adapt to climate change is linked to their direct exposure to these changes, as well as to the social and institutional structures present in each environment. Human communities that have diverse economies and are resilient to change today will also be prepared for future climatic stresses. Significant progress has been made in developing scientific principles and tools for adapting to climate change through science-management partnerships focused on education, assessment of vulnerability of natural resources, and development of adaptation strategies and tactics. In addition, climate change has motivated increased use of bioenergy and carbon (C) seques- tration policy options as mitigation strategies, emphasizing the effects of climate change-human interactions on forests, as well as the role of forests in mitigating climate change. Forest growth and afforestation in the United States currently account for a net gain in C storage and offset approximately 13 percent of the Nation’s fossil fuel CO2 production. Climate change mitigation through forest C management focuses on (1) land use change to increase forest area (afforestation) and avoid deforestation, (2) C management in existing forests, and (3) use of wood as biomass energy, in place of fossil fuel or in wood products for C storage and in place of other building materials. Although climate change is an important issue for manage- ment and policy, the interaction of changes in biophysical environments (e.g., climate, disturbance, and invasive species) and human responses to those changes (management and policy) will ultimately determine outcomes for ecosystem services and people. Although uncertainty exists about the magnitude and timing of climate-change effects on forest ecosystems, sufficient scientific information is available to begin taking action now. Building on practices compatible with adapting to climate change provides a good starting point for land managers who may want to begin the adaptation process. Establishing a foun- dation for managing forest ecosystems in the context of climate change as soon as possible will ensure that a broad range of options will be available for managing forest resources sustainably. Keywords: Adaptation, carbon, climate change, climate-change effects, climate-smart management, ecological distur- bance, forest ecosystems, mitigation, National Climate Assessment. ii Effects of Climatic Variability and Change on Forest Ecosystems: A Comprehensive Science Synthesis for the U.S. Forest Sector Acknowledgments English Equivalents The editors express their profound thanks to the many When you know: Multiply by: To find: authors who contributed excellent material to this report Millimeters (mm) 0.0394 Inches under a tight deadline. We also thank the following technical Centimeters (cm) .394 Inches reviewers who provided insightful comments and sugges- Meters (m) 3.28 Feet tions on earlier drafts, thus improving the quality of the Kilometers (km) .621 Miles final publication: Craig Allen, Dan Binkley, Barry Bol- Hectares (ha) 2.47 Acres lenbacher, Paul Bolstad, Marilyn Buford, Catherine Dowd, Square meters (m2) 10.76 Square feet Daniel Fagre, Bruce Goines, Margaret Griep, Sue Hagle, Square kilometers (km2) .386 Square miles Edie Sonne Hall, Jeffrey Hicke, Randy Johnson, Evan Megagrams (Mg) 1 Tons Mercer, David Meriwether, James Morrison, Charles Sams, Teragrams (Tg) 1,102,311.31 Tons Amy Snover, and David Theobald. Ellen Eberhardt assisted Degrees Celsius (C) 1.8 °C + 32 Degrees Fahrenheit with formatting the report and tracking many details of the editorial process. Patricia Loesche carefully edited the entire report and provided many helpful suggestions on writing quality. Robert Norheim created and revised several maps. Participants in the Forest Sector stakeholders workshop in Atlanta, Georgia, in July 2011 provided helpful input on the overall content of the report, owing in large part to the skillful facilitation and workshop design provided by Nancy Walters. Financial support for the editors and for publication was provided by the U.S. Forest Service Southern Research Station (James M. Vose), Pacific Northwest Research Station (David L. Peterson), and national research and development staff (Toral Patel-Weynand). iii GENERAL TECHNICAL REPORT PNW-GTR-870 Executive Summary discusses interrelated aspects of biophysical and socioeco-