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Redwood fog drip

dwheeler at teleport.com dwheeler at teleport.com
Thu Dec 3 12:11:27 EST 1998

The following article appeared in The Oregonian on Dec. 2, 1998, pC11-12, and
is posted as a courtesy.

Forest giants furnish water to neighbors

The dense needles of redwoods are a perfect mechanism for collecting the water
from fog.

By CAROL KAESUK YOON, New York Times News Service

	Always an a 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.    
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, 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," Dawson said. "They're
active in influencing their own environment. I've never been more wet in my
life than when I have been in the redwood forest during a major fog event.
You're soaking wet when yoiu're underneath one."	Dr. Kathleen
Weathers, forest ecologist at the Institute of Ecosystem Studies in
Millbrook, N.Y., said, "This is really imoportant, 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 the 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, Dawson measured the water dripping
off redwoods and off artificial fog collectors in forested and deforested
areas. He found that redwoods are extremely efficient producers of fog drip.
In deforested areas, which warm up and dry out quickly, it is much more
difficult to capture water from fog.  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. 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 redwood trees.

Positive feedback loop

	With redwoods thriving in a wet environment and thriving redwoods
making the environment wetter, the interaction forms a positive feedback
loop. 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 eons becuase the complex
structure so efficiently strips fog.	    "This is a story that gets
repeated in a lot of diferent 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 conservationsit 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 dry up."	 Paul Carroll, lawyer
for Friends of the Old Trees, a conservation group in California, said the
group has 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.

Difficult battle fought

	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 of
dollars.      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 built elaborate
structures -- which function like a redwood's many branches and needles -- to
capture water from rolling banks of fog.

Illustration captions:

1) Moisture-laden air from the Arctic warms as it descends over the Pacific
coast. 2) As it hits air coming off the Pacific, moisture condenses, creating
fog. 3) The fog hangs suspended over the ocean until inland air heated by the
afternoon sun rises, causing the cooler air suspended over the ocean to rush
in. 4) As the incoming fog makes contact with the redwood branches, which are
covered with dense groups of fine needles 1/2 to 3/4 of an inch in length,
the moisture accumulates and falls from the branches to the vegetation and
soil below. 5) The fog drip reduces temperature and raises relative humidity
during summer droughts. A relatively small 100-foot-tall redwood can gather
the equivalent of four inches of rain in a single evening. 6) Portions of the
fog drip are then absorbed into the tree's internal water system. Columns of
water are drawn up the tree's tissues from roots to leaves by dragging water
up the sapwood, molecule by molecule. Large redwoods release hundreds of
gallons of water vapor daily through their foliage, about twice the average
use of water for a household of three.

Where does the drip water go? 40% - either evaporates or works its way
through the ground to the local water system. 25% - moves by runoff toward
the ocean 35% - of water is absorbed by roots, which grow only 10-13 feet
deep but spread up to 80 feet wide to absorb the fog drip.

Posted as a courtesy by:
Daniel B. Wheeler

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