Tropical Forests not the carbon sinks they were once thought to be

Daniel B. Wheeler dwheeler at
Fri Apr 26 19:18:03 EST 2002

>From The Oregonian, Apr. 17, 2002, p B2 (Science)

Scientists recalibrate tropical rain forests' carbon absorption
By RICHARD L. HILL, The Oregonian
	Tropical rain forests may not be the carbon-absorbing sponges they
were thought to be, a new study suggests.
	The amount of carbon dioxide given off by rivers, streams and flooded
areas of tropical forests is three times that of some current
estimates, according to a research team led by Jeffrey Richey, a
professor of oceanography at the Un                                   
                                                   levels are
underestimating the amount of carbon dioxide in the air in and above
tropical forests, the new figures indicate. Richey and his colleagues
say their new numbers for waterways indicate that the amount of carbon
dioxide is about even, with as much being released as being absorbed
by the forests.
	Their calculations are based on water chemistry measurements made by
groups that Richey led in the central Amazon Basin.
	The researchers' efforts were aided by data from a new type of radar,
a Japanese system used on satellites that can measure the extent of
water. They obtained the data through NASA's Large-Scale Biosphere
Atmosphere Project.
	The study area in Brazil covered nearly 700,000 square miles, more
than four times the size of California. Water covers about 8 percent
to 20 percent of the study area, depending on the time of year and the
amount of flooding.
	Other researchers were from the University of California at Santa
Barbara, the University of South Carolina and the Centro de Energia
Nuclear na Agricultura in Sao Paulo, Brazil.

Comment by poster: while this will be surprising to some people, I
have personally felt the carbon sink status of tropical rain forests
such as the Amazon where yielding too much oxygen as first reported or
suspected. The reason: in the tropics, fungi and insects, much more
abundant than in temperate rain forests, degrade leaf and twig debris
much more quickly than in the temperate zone. In the Amazon, for
example, a leaf is degraded within 6 weeks to 6 months; in Oregon, a
Douglas-fir needle takes up to _7 years_ to degrade, but may sustain
millions more small soil-building organisms during that time. Over
time, the accumulated biomass in the process of decomposition on the
forest floor builds up, causing greater fire danger. Temperate forests
also clean water, increase soil fecundity, and support far more fungi
than in tropical rain forests.

While there are much more large insects and animals in tropical rain
forests, and often much more brilliantly colored; carbon sinks
actually release their stored carbon much slower in temperate forests,
where degradation takes much longer. That's one reason why old-growth
forests are so important: they have sequestered carbon for much longer
than most other life on earth, and take a relatively longer time to
re-release those nutrients back into the carbon cycle.

Daniel B. Wheeler

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