Forests on the East Coast of North America

Every spring, as the weather warms, trees in forests up and down the east coast explode in a bright green display of life as leaves fill their branches, and every fall, those same leaves provide one of nature's great color displays of vivid yellow, orange and red.

Over the last two decades, spurred by higher temperatures caused by climate change, Harvard scientists say, forests throughout the Eastern U.S. have experienced earlier springs and later autumns than ever before.

Using a combination of satellite imagery, tower-mounted instruments and on-the-ground observations, research associate Trevor Keenan and Andrew Richardson, associate professor of Organismic and Evolutionary Biology, along with colleagues from 7 different institutions, found that forests throughout the eastern US are showing signs of spring growth earlier than ever, and the growing season in some areas extends further into the fall. That expanded growing season, they say, has enabled forests to store as much as 26 million metric tons more CO2 than before. The study is described in a June 1 paper published in Nature Climate Change.

"What we find in this paper is an increase in the growing season of forests in the eastern U.S. due to recent climate change," Keenan said. "This has been beneficial for forests in the past, but we do not expect the response to continue unchecked in the future. It must also be kept in mind that this positive effect of warming is but one amid a barrage of detrimental impacts of climate change on the Earth's ecosystems."

Though the fact that forests can store more carbon is a good thing, both Keenan and Richardson warned that continued climate change could lead to more dramatic negative consequences in the future.

"If forests weren't storing additional carbon in this manner, we would be even worse off in terms of atmospheric CO2 levels, so at the moment, it's a good thing…but this is not going to solve the CO2 problem," Richardson said. "Yes, 26 million metric tons is a lot of carbon, but it's still small when compared to fossil fuel emissions.

"And climate change isn't just about warmer temperatures," he continued. "It's also about changes in precipitation patterns…so in the future, an earlier spring might not help forests take up more carbon, if they end up running out of water in mid-summer."

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