February 2, 2010
Geoffrey Parker has been tracking the growth of trees since September 8, 1987—his first day working as a forest ecologist at the Smithsonian Environmental Research Center (SERC) in Edgewater, Maryland.
Parker estimates that he and his colleagues have made about 250,000 measurements of tulip poplars, sweetgums, American beeches, southern red oaks and others in 55 designated plots. The plots are stands of trees that range in age from five to 225 years. Since the plots represent the forest at different stages of development, the researchers have been able to use them to create a “chronosequence” from which growth predictions can be made.
However, according to a study by the scientists in this week’s Proceedings of the National Academy of Sciences, more than 90 percent of the trees monitored grew two to four times faster than they predicted. And it’s a recent phenomenon. They have found that the forest, on average, is growing by an additional two tons per acre annually—an amount that translates to a new tree with a diameter of two feet each year.
Parker and his team attribute the growth spurt to climate change, particularly the rising levels of carbon dioxide in the atmosphere, higher temperatures and longer growing seasons. According to measurements taken at SERC over the past 22 years, carbon dioxide levels at the scientific facility have risen 12 percent, mean temperature has increased by almost three-tenths of a degree and 7.8 days have been tacked on to the growing season.
“We suspect this is a widespread trend,” says Parker. “Other researchers may have similar data but have not yet examined it in the way we have.”
The finding raises new questions. Parker wonders if the accelerated growth is affecting the trees’ cycling of carbon, water and nutrients and how much longer this growth spurt can continue.
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