Erik Stokstad has a story in Friday's Science (paid sub. req.) about a research team creating artificial droughts in the Amazon to try to understand the implications of climate change on the rain forest:

What's worrisome is that when drought lasts more than a year or two, the all-important canopy trees are decimated. Everyone knows that a lack of water eventually kills plants. But by pushing the tropical forest to its breaking point, researchers now have a better idea of exactly how much punishment these forests can withstand.

These kinds of data will be indispensable for predicting how future droughts might change the ecological structure of the forest, the risk of fire, and how the forest functions as a carbon sink, experts say. Given that droughts in the Amazon are projected to increase in several climate models, the implications for these rich ecosystems is grim, says ecologist Deborah Clark of the University of Missouri, St. Louis, who works at La Selva Biological Station in Costa Rica. The forests are "headed in a terrible direction," she says. What's more, the picture includes a loss of carbon storage that might exacerbate global warming.