Climate Change and America's Forests

A supporting technical document to the 1989 RPA Assessment

The timber projections in the RPA Assessment assume a future in which the climate follows historic trends and in which changes in timber production and land use are an outgrowth of these trends, not abrupt discontinuities from the past. These assumptions may not be met if the earth's climate changes rapidly.

Our perception of change is often associated with seasonal to decadal regional weather changes, such as the summer drought of 1988 or the hot, dry years in the 1980s; and local to regional environmental changes, such as the impact of acid-rain or urban smog on vegetation. As we begin to understand the earth system, we need to consider long-term changes, such as those changes associated with global climate. There is great uncertainty in the projections of climate change on local ecosystem responses. However, we can say that these factors will play a major role in abrupt changes in the landscape: changes in precipitation and, to a lesser extent, temperature will restrict the persistence of ecological systems; and changes in disturbances, such as fire, insects, and disease, will impose new and different stresses on ecosystems. There is great need to determine the impact of this potential climate change on North American ecosystems and, in particular, our forest resources. Reliable estimates of the magnitude and rate of climate change are needed at many decision levels within society: individuals, industry, and governments. This document summarizes the current research on the impacts of climate change on America's forests.

While we have yet to detect the first signals of greenhouse warming, either through direct measurements of temperature or through impacts on forest ecosystems, we need to begin preparing for the inevitable changes. Our policy options are to conserve what we currently have in forest resources, to develop strategies to mitigate the effects of climate change, to adapt to change, or some combination of these three options. Each of these options raises many questions concerning management actions and our understanding of forest ecosystems.

The conservation option is undoubtedly the most difficult to achieve. In those areas where forest productivity will be significantly reduced, many resources will be diminished. While we could conserve some elements, albeit at a high cost, the external force, climate, will ultimately prevail. Different ecosystems will evolve in those areas where the future climate significantly differs from the current situation. Conservation actions might include installation of irrigation systems in plantations, or use of fertilizers to compensate for reductions in growth rates. The implementation of such conservation actions raises a policy question of future land use. Which forest types should be conserved, if any, and where should they be conserved? Competition for land use will be strong because other uses, such as agriculture or urban area will also be adjusting to climatic change.

The second option, mitigating the effects of climate change, involves the global community. Energy conservation or use of nonfossil fuel energy will slow global warming. Such actions require a global policy rather a local land management policy. Energy conservation or use of alternate energy sources can control the rate of greenhouse gases build-up, but cannot reverse the build-up of greenhouse gases that has already occurred in the atmosphere. Vegetation production removes carbon dioxide from the atmosphere and stores some of it as carbon either in wood aboveground or as roots below ground. Through aggressive reforestation and afforestation, we can offset some of the anthropogenic trace gases. To effectively accomplish accelerated tree planting on nonfederal lands would require close coordination and cooperation among federal and state forestry professionals, consulting foresters, and the tree nursery industry to ensure adequate supplies of quality trees of appropriate species were available to private landowners and local communities. Management questions that need to be answered include what tree species and where. Sustained technical assistance would be required to ensure that proper planting, silvicultural treatments, and tree maintenance take place.

The third option, adaptation, offers the greatest flexibility in managing forests in a changing climate. Adaptive strategies involve developing new technologies to use the resource of the future forest, importing new industries or businesses which are compatible with the resources of the future forest, or relocating existing activities in anticipation of a changing climate. Adaptive strategies also include developing or introducing species which are compatible with the changing climate.

Because forests are complex ecosystems, and because uses of the forests are so varied, there is no set formula which can be prescribed for all forests. Future forest management will undoubtedly contain elements of all three options to address the problems arising from global change. Because of the uncertainties in the current prediction of impact of climate change on America's forests, we will need to continue careful monitoring and surveillance of our forest ecosystems, particularly those components which are highly sensitive to the greenhouse effect in order to refine management strategies. Also, because our current capability to predict impacts is imprecise, we must continue to carry out research on the effects of multiple stresses on our forests in order to assure their health and productivity in a changing atmospheric environment.

Joyce, Linda A.; Michael A. Fosberg, and Joan M. Comanor. 1990. Climate Change and America's Forests. General Technical Report RM-187. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 12 p.