Giants in the mist

Giant redwood trees seem to water their own habitat

Last Updated: Saturday 04 July 2015

 Car and the beanstalk: A redw (Credit: vadim v aristov)those who have seen them say its an awe-inspiring sight: giant redwood trees in the fog. Towering above all other vegetation, these ancient biological wonders stand like mythical giants shrouded in the mist. It is a timeless landscape. But now, scientists think that the fog that wraps these giants in cloudy, wispy covers might be performing a more crucial biological role than merely a decorative one. They also think that the fog might finally reveal why redwoods are the tallest trees on Earth.

Scientists have always known that water suspended in the fog drips down the trees' limbs, needles and trunk. Now, Todd Dawson, plant ecologist at Cornell University and University of California at Berkely, usa , says that this curious mechanism provides an immense amount of water not only to the trees but also to the ground around them. His study, published in January 1999, contradicts a long-held piece of ecological dogma that plants 'steal' water rather than contribute it to their habitat.

On a foggy night, a single redwood tree can douse the ground beneath it with the equivalent of a drenching rainstorm and the drops off the redwoods can provide as much as half the water coming into a forest over a year. In fact, this unique ability to draw water out of a fog is important for maintaining the wet climate these and other trees -- some endangered -- thrive in, says Dawson. "Plants are not passive players out there, they are actively influencing their own environment," he says.

Kathleen Weathers, forest ecologist at the Institute of Ecosystem Studies in Milbrook, New York, thinks the redwoods are playing an extremely vital role: "if you cut redwoods down, you take away a structure that can intercept fog and the water will pass right by."

Conservationists working to save these charismatic trees have long maintained that this fog drip is essential not merely for the plants but many animals living within these forests. The phenomenon is also of immense value to humans -- the people struggling to maintain water supplies in habitats that see very little or no rain in the summers. Coastal redwoods ( Sequoia sempervirens ) are found in patches along the us 's California coast and also into southern Oregon.

Working in Northern California, Dawson measured the water dripping off redwoods and artificial fog collectors in forested and deforested areas. He found that the trees are extremely efficient producers of fog drip. In deforested areas, which warm up and dry quickly, it is much more difficult to capture water from fog.

Dawson says the redwoods are life-savers to many other plants. Ferns, he points out, depend entirely on the redwood fog drip for their water supplies. He believes that the giant structure of these trees evolved over millions of years primarily to draw water from the fogs.

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