Magazine article Science News

Trees' Growth Keeps Climbing with Age: Oldest Specimens Pack on Weight Fastest, Making Them Excellent Carbon Collectors

Magazine article Science News

Trees' Growth Keeps Climbing with Age: Oldest Specimens Pack on Weight Fastest, Making Them Excellent Carbon Collectors

Article excerpt

As trees grow older and bigger, they bulk up faster and faster, researchers report January 15 in Nature.

The findings revise scientists' understanding of big trees' role in stockpiling carbon drawn from the air.

"This will come as a surprise for many people," says Maurizio Mencuccini, an ecologist at the University of Edinburgh. "The basic perception is that trees are less capable of growing as they age."

For years, many scientists believed that trees' growth was quick in the beginning and tapered off in old age. But the evidence for this pattern is mostly indirect, says study coauthor Nathan Stephenson, an ecologist at the U.S. Geological Survey in Three Rivers, Calif.

In a forest with trees of the same age, scientists have found that productivity--the mass of all the limbs, branches and trunks in a forest--tends to decline over time. And the leaves of big, old trees don't convert sunlight into sugar as well as the leaves of small, young trees do.

"The in-between scale-the individual tree--has tended to be ignored," Stephenson says.

Though some researchers have suggested that trees' growth rate increases continuously rather than declining, until now no one had examined a large collection of individual trees. So Stephenson and colleagues measured the diameters of thousands of trees in California's Sierra Nevada mountains and teamed up with other scientists who had collected similar measurements on forested continents around the world. The researchers estimated the growth rate of each tree from two measurements, taken on average five to 10 years apart. …

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