To obtain sufficient moisture for photosynthesis and growth, redwoods reach into the air with leaves shaped like baseball mitts and capture the fog that rolls in by night and languishes through most mornings. "From 25 to 40 percent of the moisture in the system comes from fog," says Dawson, who has been studying the relationship between the coastal fog and the redwoods for two decades. Some of the fog simply covers the leaves and prevents evaporation. But some of it also enters the stomata, or tiny pores, on the leaves and is drawn down through the branches to the roots. This is the reverse of transpiration, the normal flow of water from the roots to the leaves that exists in most trees. Redwoods are the first trees found to move water in both directions, though others have been identified.
Fog is not just a vital element for the redwoods—it's also crucial to the entire redwood forest ecosystem. Some of the moisture drips off the redwood leaves, landing on the forest floor to water the trees and young saplings. "It's not just a drip, drip, drip," says ecologist Holly Ewing of Bates College in Lewiston, Maine, who also worked with Dawson. "The moisture can descend into the ground up to 35 centimeters deep, and that's a lot of water."
More information at Scientific American.