Global Climate Change Model Predicts Changes In U.S. Ecosystems

January 22, 1999

Ron P. Neilson, makes his presentation, "Projections of Changes in U.S. Ecosystems and Land Cover," January 22 at the American Association for the Advancement of Science Annual Meeting and Science Innovation Exposition in Anaheim, California.

PORTLAND, Ore. January 22, 1999. What might be the impacts of global warming? How could those impacts affect forest growth, water resources, and land use? Dr. Ron Neilson, a bioclimatologist with the USDA Forest Service, has developed a computer model that simulates vegetation type in any area of the world and can determine the impact of global climate change.

Dr. Neilson's model, the mapped-atmosphere-plant-soil system (MAPSS) is one of six in the high-visibility vegetation ecosystem modeling analysis project (VEMAP) and is affecting national policy considerations on global warming, including the position the United States presented at the Framework Convention for Climate Change in Kyoto, Japan, in 1997.

"To make a fully dynamic model," Neilson says, "you must include vegetation distribution and vegetation productivity. Disturbance by fire should be thrown in as a third ingredient. You can then make quantitative predictions about vegetation, natural disturbance, and hydrolic change. In the future, these new dynamic models will allow you to get feedback between vegetation and the atmosphere."

Simulations from MAPPS show great changes in the United States in vegetation distribution and water resources under various global warming scenarios. Mixed conifers and hardwoods in the Northeast could decrease significantly and move into Canada. Certain desert species in the Southwest could shift north as far as eastern Washington. Fire could increase over large parts of the country because of widespread drought conditions. This could occur in the Great Lakes area and in the Southeast and Northwest forests.

Vegetation growth could increase over large areas because of longer growing seasons or more rainfall. It might even be possible, under some scenarios, to grow more trees in the Great Plains, allowing more sequestration of carbon.

Annual water yield is predicted to decline dramatically over most of the Eastern United States. The mountainous West, however, produces a range of scenarios from increases to decreases in annual water yield. Under all scenarios, winter runoff would increase because of a decreased snowpack, with the possibility for widespread flooding in the West.

What can be done to manage global warming? "These changes likely will result in large regional upheavals and require significant and very careful management," says Neilson. "For example, if forests over large areas begin to undergo drought stress, it might be prudent to 'trim the wick' or use some form of density control to save trees and conserve water in streams. Another alternative is to use the landscape as a 'carbon pump' and move rapidly growing forests over short rotations into long-lived forest products like houses and furniture. Careful balance of these considerations may be required."

Neilson's study provided mapped vegetation change assessment products to Federal agencies for use in national and international assessments of the impacts of global warming on natural vegetation.
Scientist Profile:
Ronald P. Neilson is an internationally recognized bioclimatologist and is team leader of the Mapped-Atmosphere-Plant-Soil System team, Pacific Northwest Research Station, USDA Forest Service. He is based at the Agency's laboratory in Corvallis, Oregon. Neilson received his Ph.D. at the University of Utah and is a courtesy professor at Oregon State University. He has been developing his global change model since 1988. He is a 1987 recipient of the Cooper Award, Ecological Society of America.

Nielson can be reached at:

Pacific Northwest Research Station/USDA Forest Service
Corvallis Forestry Sciences Laboratory
3200 SW Jefferson Way
Corvallis, Oregon 97331
e-mail: rneilson/
Phone: (541) 750-7303

USDA Forest Service - Pacific Northwest Research Station

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