NY Times, November 24, 1998
(Section D, Page 1)
Clues to Redwoods' Mighty Growth Emerge in Fog
By CAROL KAESUK YOON
Always an awe-inspiring sight, the giant redwoods that tower along the
California coast are perhaps at their majestic best on foggy days, when
these ancients, among the botanical wonders of the world, can be
glimpsed through wisps of swirling mist.
But now scientists are learning that fog among the redwoods is more than
just picturesque. They believe fog may be crucial to the well-being of
these rapidly disappearing forests and an answer to the long-pondered
question: Why are redwoods the tallest trees on earth?
Scientists have long known that when fog rolls into a redwood, water
suspended in the fog begins dripping down the tree's limbs, needles and
trunk. But in a study to be published in January in the journal
Oecologia, Dr. Todd Dawson, a plant ecologist at Cornell University and
the University of California at Berkeley, has shown that this curious
mechanism can provide an immense amount of water to the trees -- and to
the ground around them. The
study overturns a major piece of ecological dogma, that plants steal
water rather than contribute it to a habitat.
In one foggy night, a single redwood can douse the ground beneath it
with the equivalent of a drenching rainstorm and the drops off redwoods
can provide as much as half the water coming into a forest over a year.
In fact, Dr.Dawson concluded, the redwoods' ability to draw water from
fog appears crucial in maintaining the wet climate that they and so many
other species, some endangered, thrive in.
"Plants aren't passive players out there," Dr. Dawson said. "They're
active in influencing their own environment. I've never been more wet in
my life than I have been in the redwood forest during a major fog event.
You're soaking wet when you're underneath one."
Dr. Kathleen C. Weathers, forest ecologist at the Institute of Ecosystem
Studies in Millbrook, N.Y., said, "This is really important, not just
for redwoods but for the other plants. If you cut the redwoods down, you
take away that structure that can intercept the fog and the water will
pass right by."
Conservationists working to save these charismatic trees, which can
inspire people to extremes of impassioned zeal, have long argued that
fog drip is vital not only for plants, but for endangered animal
species, as well as the people who struggle to maintain water supplies
in habitats that can see little or no rain in the summer. Coastal
redwoods, or Sequoia sempervirens, are found patchily mostly along the
California coast and into southern Oregon.
Working in Northern California, Dr. Dawson measured the water dripping
off redwoods and off artificial fog collectors in forested and
deforested areas. He found redwoods are extremely efficient producers of
In deforested areas, which warm up and dry out quickly, it is much more
difficult to capture water from fog.
Dr. Dawson also took advantage of the fact that not all water is created
equal. Hydrogen and oxygen, the two components of water, come in
different forms, or isotopes. Fog water and rainwater can be
distinguished from one another by the varying ratio of isotopes they
contain. Studying the isotopes in water in different plants, Dr. Dawson
found that fog drip was an important source of water to redwoods as well
as many other plants. He said sword ferns were at times entirely
dependent on the water coming off of redwood trees.
With redwoods thriving in a wet environment and thriving redwoods making
the environment wetter, the interaction forms a positive feedback loop.
Dr. Dawson said even the handsome structure of a redwood itself may help
with this feedback. Redwoods may have evolved their structure of many
branches and an array of fine needles over the aeons because the complex
structure so efficiently strips fog.
"This is a story that gets repeated in a lot of different environments
around the world," Dr. Tom Hinckley, forest biologist at the University
of Washington, said of the interaction between fog and trees. "Until now
these fog phenomena have been largely discounted."
For local activists who live in and around redwood forests, scientific
confirmation of their theories was good news.
"When you clear cut, you don't have any input from the fog," said Els
Cooperrider, a redwood conservationist and local radio talk show host,
who said she has made fog drip a household word in Mendocino County.
"One of the reasons so many people around here have begun to listen to
this phenomenon of fog drip is that they've seen their wells and springs
Paul Carroll, lawyer for Friends of the Old Trees, a conservation group
in California, said the group had already used fog drip as an arguing
point to stop logging. Twice, the group prevented cutting in a redwood
forest using the objection that the loss of water from fog drip was not
addressed adequately in the logging plans that had been submitted.
Conservationists are fighting a difficult battle as researchers say only
4 percent of the original redwood forest remains standing today and a
single old growth redwood can contain wood worth hundreds of thousands
Dr. Dawson said it remained an open question whether the fog water he
studied replenished streams or ground water.
Among those eager for answers are biologists interested in the fate of
endangered species like the Coho salmon, whose streams run through
redwood forests before reaching the sea.
"I can see this being hugely important," said Dr. Terry Roelofs, salmon
stream ecologist at Humboldt State University in Arcata, Calif.,
explaining that the time Coho spend in shallow, drying streams in the
summer can be a crucial bottleneck for these fish.
"If fog drip contributes to stream flows that would be a real plus for
these animals," he said.
While new to biologists, the idea that fog can be a crucial source of
water has in fact been around for some time.
In coastal regions of South America and in Namibia, where fog is common
but water is not, people build elaborate structures -- which function
like a redwood's many branches and needles -- to capture water from
rolling banks of fog.
Whatever else biologists may learn about redwoods, the most stunning
thing about them remains their sheer, jaw-dropping size.
Dr. John Sawyer, vegetation ecologist at Humboldt State University, said
the tallest tree alive in the world today is a 370-foot-tall redwood
whose location biologists declined to disclose, to protect its fragile
habitat from visitors.
But given the physical challenge of moving water up to high leaves and
branches, biologists have long wondered how redwoods achieved their
Plants do not have an active pumping system to move water and depend
on the evaporation of water out of the leaves, an action that draws up
more water from below. But this passive movement of water has to be
strong enough to overcome the resistance within the pipe-like structures
that transport water throughout a plant, and the taller the pipe the
greater the resistance. With too much resistance a plant can suffer a
break in the water column, which could stop the flow of water
In a new book on redwoods scheduled to be published next fall by Island
Press, Dr. Dawson has contributed to an article that suggests that the
ability of redwoods to keep their environment so moist with fog water
may reduce the rate at which they lose water and the rate at which water
must move up through them, thereby reducing the water demands that keep
other plants from growing to such great heights.
In addition, Dr. Dawson said it was possible that redwoods were taking
in fog water through their foliage, an ability that could greatly reduce
their need to move quantities of water upward.
Dr. Reed Noss, co-director of the Conservation Biology Institute and
editor of the upcoming volume on redwoods, said that understanding the
relationship between fog drip and the stupendous height of redwoods was
more than a mere curiosity.
"It tells us something about restoration," said Dr. Noss. If it is the
presence of a lot of big, fog-stripping redwoods that allows redwoods to
soar skyward, he asks, "once we deforest a site, will we ever be able to
grow these giants back?"
Tuesday, November 24, 1998
Copyright 1998 The New York Times
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