By Steven McNulty, U.S. Department of Agriculture, Forest Service

Environmental factors controlling forest distribution and growth vary across the nation (Figure 1). Precipitation, minimum and maximum air temperature, or soil conditions can dominate ecosystem structure and function, depending on geographic location. During the past decade, field observation and experimentation have been combined with forest process models to examine the impacts of changing precipitation, air temperature, ozone, and carbon dioxide on forest structure and function. This research suggests that the impacts of climate change will not be uniform across all forests types.

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Tree species that currently exist within a narrow range of soil or climate conditions are particularly vulnerable . For example, spruce-fir forests are often located across a narrow elevational range in mountainous areas where climate and soil conditions provide them with a competitive advantage over other tree species. In warmer areas below this elevational range, hardwood forests dominate. In colder areas above the elevational range of spruce-fir, climate and soil conditions restrict vegetative growth. Under a warmer environment, hardwood forests will move to higher elevations; however, spruce-fir forests will be limited from also moving to higher elevations due to poor soil conditions in those areas.

 Therefore, spruce-fir forests could be replaced with hardwood stands across much of the country. Similarly, the competitive advantage that other forest types have developed to survive in very dry or wet environments may also be disrupted by climate change. The rate of potential climate change that forests are subjected to may be faster than the rates at which they can adapt. This could result in specific forests being displaced or in species extinction. Therefore, the degree of climate change, geographic location, and forest species composition will all contribute to the positive or negative impacts of climate change across the country.

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The ecological and economic importance of forests varies across the nation. For example, in the southern U.S., much of the forested land is intensively managed for lumber production, while mid-west forests serve more of a recreational purpose. In addition to ecological and economic considerations, forests and soils may be important sinks of atmospheric carbon dioxide. Relatively young forests that are strong carbon sinks cover much of the U.S, providing an important link to changes in atmospheric carbon dioxide concentrations.

For the national forest sector assessment, discussion of climate change impacts on the forest sector will be compiled from the twenty regional workshops. Other components of the forest sector, including recreation, wildlife diversity, population size, and water use and yield, may also be impacted by climate change. To examine these components, the forest sector assessment team has formed a committee to compile, review and present the available information from many published sources including the United States Resource Planning Assessment Report and the Vegetation/Ecosystem Modeling and Analysis Project.

The forest sector committee is co-chaired by Dr. John Aber of the University of New Hampshire IN Durham, NH and Dr. Steven McNulty of the USDA Forest Service IN Raleigh, North Carolina. The sector team will develop alternate impact projections and mitigation strategies based upon the scenarios supplied to the sectors. Working drafts of the assessment will be posted to the sector web site to solicit public comments. For the latest status and information on the forest sector assessment, see the sector web site.

For more information, contact:

Steven McNulty, USDA Forest Service; 1509 Varsity Dr., Raleigh, NC 27606; phone: (919) 515-9489; email: mcnulty@arrc.ncsu.edu.