Increased levels of carbon dioxide in the atmosphere are apparently causing forests in the eastern United States to grow faster, a new study says. Trees observed along the Chesapeake Bay in Maryland are growing two to four times faster than during earlier periods, and mixed hardwood forests are 
packing on an additional two tons of growth per acre, according to a report published in The Proceedings of the National Academy of Sciences. After controlling for other variables, researchers say the likely cause is higher levels of CO2. Because trees absorb and store carbon dioxide, they are an important factor in counteracting global warming. “My guess is that they are already sopping up some of the extra carbon,” said Geoffrey G. Parker, an ecologist at the Smithsonian Environmental Research Center and co-author of the study. The rate of growth is tracked by measuring tree diameter. How long this accelerated growth can be sustained is uncertain, however, since the growth rate depends on other factors, including water availability and soil nutrients. Since 1987, Parker has studied 55 stands of trees that are representative of other forests in the eastern United States.
An American sycamore