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Basic biology suggests that plants might grow faster in a world with more carbon dioxide, and field experiments bear that out: when you pump extra CO2 into a field or a forest, trees and other vegetation tend to get bigger...
That question is a long way from being answered, but a study published recently in the Proceedings of the National Academy of Sciences takes a small step in that direction. A team of researchers used 22 years' worth of carefully accumulated measurements of hardwood forests in and near the Smithsonian Environmental Research Center, in Edgewater, Md., to show that their growth has accelerated significantly. On average, the stands were expanding at a rate of two extra tons of mass per acre per year, by the end of the study - the equivalent of a single two-foot-diameter tree...
What made the study possible in the first place was the fact that pretty much none of the forest in this part of the U.S. is virgin; it's been cleared for agriculture at various times, and then allowed to regrow in patches. The result: individual stands of similar trees ranging from about 225 years old to just five. "You could do this experiment by measuring a single stand of trees as long as possible," says Parker, "but a scientific career lasts only a few percent of the life of a tree." This way, he explains, you have a snapshot...
...Forest biologists already know that, all things being equal, trees grow more rapidly when they're young, then taper off as they mature, and that you can chart the standard curve of growth for a given forest type by looking at the kind of snapshots Parker and his colleagues used. It takes only a couple of years of measurements to figure out the overall growth curve. This study has been going on for 22 years, conducted largely by technicians and volunteers trained by the Smithsonian scientists. "We have a huge corps of volunteers," says Parker. "It's not rocket science...
...Smithsonian experiment will continue to see what happens next in terms of forest growth, says Parker. His suspicion: because the trees aren't getting a boost in nutrients to match the extra CO2 and warmer climate, "it probably can't go on much too much longer...