After all that talk, it seems that forests might not do such a great job sucking carbon dioxide emissions out of the air, according to two studies published today in the journal Nature. During negotiations over a climate change treaty, the U.S. and Canada have made a big to-do about the potential for forests to act as carbon sinks, arguing that countries should get credit for reducing greenhouse gas emissions if they have big forest reserves or plant new trees. But Duke University researchers in one of the studies exposed pine trees to elevated levels of CO2 and found that after an initial growth spurt, the trees grew more slowly and didn’t absorb as much carbon as expected. In the second study, researchers from Duke and Bowdoin College found that carbon returns to the atmosphere, rather than being incorporated into soil, as organic material in the soil around trees decomposes.