From: LARRY KLAES (ljk4_at_msn.com)
Date: Sat Mar 22 2003 - 05:17:58 PST
----- Original Message -----
From: Mark Hess
Sent: Friday, March 21, 2003 5:05 PM
To: News Media list.serv
Subject: GSFC 03-32 / FIRE FREQUENCY DETERMINES FOREST CARBON STORAGE
Rob Gutro March 21, 2003
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-4044)
Rgutro_at_pop900.gsfc.nasa.gov
Barbra Rodriguez
The University of Texas at Austin
(Phone: 512/232-0675)
brodriguez_at_mail.utexas.edu
Release No. 03- 32
FIRE FREQUENCY DETERMINES FOREST CARBON STORAGE
Scientists studying trees ranging from saplings to 130 years old in
Canada's northern forests have discovered that the period since a
fire last swept through an area determines how much carbon the forest
can store. Twenty to forty year old stands absorb more carbon than
those 70 years old and older, despite being smaller and having less
biomass or plant material.
Boreal or northern forests account for close to 25 percent of total
carbon stored in vegetation and soils in the Earth's biosphere.
Wildfires burn down individual areas every 40 to 250 years and are an
important part of this ecosystem. Whether or not these forests are
likely to lower or raise levels of carbon dioxide in the atmosphere
depends on how these carbon reserves respond to, and recover from,
both climate change and disturbances such as wildfires.
NASA funded part of this study under its Earth Science Enterprise
(ESE), whose mission is to understand and protect our home planet.
Earth Science in NASA seeks to understand trends in land cover and
land use, such as forest fires, that drive global climate. Another
Earth Science program objective is to understand the Earth system's
response to natural and human-induced changes, and effects on global
carbon cycle.
Marcy Litvak, plant ecologist at The University of Texas at Austin
and lead author of the study that appeared in a recent issue of the
Journal of Geophysical Research -
Atmospheres, said that the ability of tree stands to store carbon
changes as they regenerate from fire. Forests will store more or less
carbon depending on the dominant tree species, the amount of moss
cover, and changes in forest structure due to fire. Those factors
determine how much total carbon is exchanged with the atmosphere.
Carbon is transferred from the atmosphere to the forest through the
process of photosynthesis. Carbon is returned to the atmosphere
through the process of respiration as soil microorganisms decompose
dead organic matter, and trees and mosses metabolize the products of
photosynthesis. It is the balance between these two processes, taking
in carbon during photosynthesis and "exhaling" carbon through
respiration, that determines how much carbon is stored in the forest.
Between 1999-2000, Litvak and her colleagues, Scott Miller and
Michael Goulden of the University of California, Irvine, and Steve
Wofsy of Harvard University, used solar-powered anemometers and
infrared gas analyzers mounted on towers to monitor carbon emissions
over five black spruce stands in Manitoba, Canada. These stands
ranged in age from 11 to 130 years old. Results indicate that the
ability to store carbon is almost zero in the 11 year-old stand,
increases to a maximum in the 36 year-old stand, then gradually falls
back down to zero in the 130-year old stand. They concluded that most
of the net carbon absorption appears to take place from 20-50 years
after a fire.
"Seedlings of Aspen, Jack Pine, and Black Spruce all regenerate
simultaneously following wildfire in areas once dominated by mature
black spruce forests in this region of Manitoba. Aspen and Jack
Pine tend to dominate in young stands where light is not limited.
Black Spruce grow the slowest, but eventually out-compete the Aspen
and Jack Pine by blocking the sunlight available to these species. By
70 years following a burn, these forests are dominated by Black
Spruce once again," Litvak said.
Stands less than 20 years old store less carbon than older trees
because they lack sufficient leaf area for rapid carbon accumulation.
Carbon storage is highest in stands 20-50 years old that are
dominated by rapidly growing aspen trees that take up carbon at
higher rates than black spruce and jack pine trees.
"Stands [of trees] older than 70 years are dominated by black spruce
trees and thick moss cover that 'exhale and inhale' equal amounts of
carbon. That means stands older than 70 years are in near carbon
balance with the atmosphere," she said.
Knowing the rate at which trees respire will help scientists to
better estimate the trees' contributions to the global carbon cycle.
This is especially important because of the changing climate.
"Increased fire frequency, as predicted from global warming
scenarios, has the potential to significantly impact the contribution
boreal forests make to the global carbon cycle," Miller said.
NASA data from the Boreal Ecosystem-Atmosphere Study (BOREAS) was
also used in the study. BOREAS was a large-scale international
experiment in the northern forests of Canada between 1993 and 1996,
whose goal was to improve understanding of interactions between the
boreal forest and the atmosphere, and clarify their roles in global
change.
This work was supported by NASA, the National Science Foundation, and
U.S. Department of Energy.
For more information and images, see:
http://www.gsfc.nasa.gov/topstory/2003/0311firecarbon.html
The Boreal Ecosystem-Atmosphere Study (BOREAS):
http://www-eosdis.ornl.gov/BOREAS/bhs/BOREAS_Home.html
http://www.daac.ornl.gov/BOREAS/boreas_home_page.html
*****************************
Mark S. Hess
Chief, Office of Public Affairs
NASA/GSFC, Code 130
E-Mail: Mark.S.Hess_at_nasa.gov
Phone: 301 286-6255
Fax: 301 286-1707
*************
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