Trees with a thirst for fog.

Fog may be the unsung hero of certain forests While common sense might dictate that rain or snow supplies the water used by vegetation, a study conducted on California's Point Reyes peninsula suggests that some trees also depend on fog water.

Neil Ingraham of the Desert Research Institute in Las Vegas and his colleagues at the University of California, Davis, analyzed water from the interior of trees at three locations on the peninsula - an area bathed in fog during summer and moistened by rain in winter. Because fog water and rain have different ratios of hydrogen and oxygen isotopes, the scientists were able to determine which kind of water the trees had absorbed. At one location, trees used rainwater during the rainy season and fog water during a foggy season. At another site, trees seemed to use fog water year-round, while trees at the third spot used only rainwater. This is the first study to document the uptake of fog water by trees, Ingraham says.

Trees don't absorb fog moisture directly out of the air, but instead use their leaves as a sort of collecting net. As the fog blows in, water droplets collide with the leaf surface. Coalescing into larger droplets, they drip to the ground and then soak into tree roots. Ingraham says his group's findings suggest it may be impossible to regenerate certain forests that have been cleared. If the trees depend on fog water, then cutting the forest will remove the fog-collecting system, and sprouts or young trees may not be able to catch enough fog water to sustain themselves, he says.