Foreword

Forests & Global Climate Change: Potential Impacts on U.S. Forest Resources

Eileen Claussen, President, Pew Center on Global Climate Change

Approximately one-third of U.S. lands are covered by forests, which makes forest ecosystems prominent natural resources that contribute to biodiversity, water quality, carbon storage, and recreation. Forests also play a significant role in the U.S. economy, and forestry or forestry-related enterprises are the dominant industries in many U.S. communities. Human-induced climate change over the next century is projected to change temperature and precipitation, factors that are critical to the distribution and abundance of tree species.

Forests and Global Climate Change is the ninth in a series of Pew Center reports examining the potential impacts of climate change on our environment and health. A previous report in this series addressed the risks to terrestrial ecosystems posed by climate change. This report details the likely ecological and economic impacts of climate change over the next century on the U.S. forestry sector. Key findings include:

Forest location, composition, and productivity will be altered by changes in temperature and precipitation. Climate change is virtually certain to drive the migration of tree species, resulting in changes in the geographic distribution of forest types and new combinations of species within forests. Generally, tree species are expected to shift northward or to higher altitudes. In addition, climate change is likely to alter forest productivity depending upon location, tree species, water availability, and the effects of carbon dioxide (CO2) fertilization.

Changes in forest disturbance regimes, such as fire or disease, could further affect the future of U.S. forests and the market for forest products. Increased temperatures could increase fire risk in areas that experience increased aridity, and climate change could promote the proliferation of diseases and pests that attack tree species. Such disturbances may be detrimental to forests themselves, but may have a lesser impact at the market level due to salvage operations that harvest timber from dying forests.

U.S. economic impacts will vary regionally. Overall, economic studies indicate that the net impacts of climate change on the forestry sector will be small, ranging from slightly negative to positive impacts; however, gains and losses will not be distributed evenly throughout the United States. The Southeast, which is currently a dominant region for forestry, is likely to experience net losses, as tree species migrate northward and tree productivity declines. Meanwhile, the North is likely to benefit from tree migration and longer growing seasons.

As a managed resource, the implications of climate change for the forestry sector are largely dependent upon the actions taken to adapt to climate change. The United States has vast forest resources and currently consumes less timber than grows within the country each year. If professional foresters take proactive measures to substitute thriving tree species for failing species, to relocate forestry industry to productive regions, and to salvage trees during dieback, the sector may minimize the negative economic consequences of climate change.

A number of challenges currently limit our understanding of the effects of climate change on forestry. Existing projections for future changes in temperature and precipitation span a broad range, making it difficult to predict the future climate that forests will experience, particularly at the regional level. The ecological models used to relate forest distribution and productivity to changes in climate introduce additional uncertainty. Thus, current projections could fail to accurately predict the actual long-term impacts of climate change on the forestry sector.

The authors and the Pew Center gratefully acknowledge the input of Ralph J. Alig, Linda Joyce, G. Cornelis van Kooten, and William H. Schlesinger on this report. The Pew Center would also like to thank Joel Smith of Stratus Consulting for his assistance in the management of this Environmental Impacts Series.