Climate: NASA satellites see thinning forest cover

Study says mid-Atlantic region most affected

A spruce beetle infestation is thinning forests in southwestern Colorado, and in some cases, wiping out huge stands of mature trees. Photo courtesy U.S. Forest Service.

By Summit Voice

SUMMIT COUNTY — Between mountain pine beetles, sudden aspen decline, spruce beetles and ips beetles that attacked southwest Colorado piñon pines in early 2000s, a significant chunk of the state’s forests have changed significantly in the past decade.

But climate change is also driving more subtle changes in forests around the country, and on the ground, those changes may not be as easy to see as a stand of dead lodgepoles.

Using satellite images, to track vegetation patterns, NASA scientists say warmer temperatures and changes in precipitation have resulted in a significant decline in forest canopy cover.The changes were most striking in the mid-Atlantic region, where the researchers estimate that 40 percent forests have been affected.

The scientists analyzed monthly satellite images from a 10-year span (2000-2010), finding declining density of the green forest cover during summer in four sub-regions, the Upper Great Lakes, southern Appalachian, mid-Atlantic, and southeastern Coastal Plain. More than 20 percent of the non-agricultural area in the four sub-regions that showed decline during the growing season, were covered by forests.

“We looked next at the relationships between warmer temperatures, rainfall patterns, and reduced forest greenness across these regions,” said Christopher Potter, a research scientist at NASA’s Ames Research Center, Moffett Field, Calif. “This comprehensive data set gave us the evidence to conclude that a series of relatively dry years since 2000 has been unfavorable for vigorous growth of forest cover over much of the Eastern U. S. this past decade.”

Potter is lead author of the paper titled “Declining Vegetation Growth Rates in the Eastern United States from 2000 to 2010,” published by Natural Resources, Dec. 2012, (3), 184-190.

Their findings challenge earlier on-the-ground assessments that forest cover has increased in the eastern U.S. recently. The most recent studies  indicate that climate change could be having many adverse and interrelated impacts on the region. The warming climate this century has caused new stresses on trees, such as insect pest outbreaks and the introduction of new pathogens. Scientists consider both climate change and disease to be dominant driving forces in the health of forests in this region.

NASA’s technology is revealing an entirely new picture of these complex impacts. The MODIS satellite captures very broad regional patterns of change in forests, wetlands, and grasslands by continuous monitoring of the natural plant cover over extended time periods.

Now, with more than a decade of “baseline” data to show how trees typically go through a yearly cycle of leaves blooming, summer growth, and leaves falling, scientists are detecting subtle deviations from the average cycle to provide early warning signs of change at the resolution of a few miles for the entire country.

“The next studies at NASA Ames will research areas that appear most affected by drought and warming to map out changes in forest growth at a resolution of several acres,” said Potter.

This research was conducted under the National Climate Assessment as part of the United States Global Change Research Act of 1990.


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