BIOPLAN POSTING 2001-6-14

"David Duthie" <David.Duthie@unep.org>
Sent by: owner-bioplan@undp.org
05/30/01 10:33 AM

bioplan
"David Duthie" <David.Duthie@unep.org>
Dear BIOPLANNERS,

Carbon sequestration has been floated as both a potential (partial)
solution to global warming and to the biodiversity crisis at the same time.
But significant progress in this area is blighted by the difficulty of
establishing an accurate accounting system for carbon storage in both
natural and managed ecosystems.

The first posting below indicates that there might be significant carbon
storage gains to be obtained from  wide range of agricultural lands, whilst
the second posting reports on some of the most detailed quantitative
experiments on forest tree carbon sequestration undertaken to date.  These
experiments find that the law of limiting factors and compensatory
responses in complex nutrient and energy flows appear to restrain both
woody and soil carbon accumulation over longer periods of time to rates
much lower than previously predicted .

Whilst these results cannot be directly extrapolated to other forest
systems, they do indicate that carbon sequestration is no substitute for
addressing climate change directly at the level of energy consumption.

Copies of the CAST report can be requested from the contact at the end of
the first posting.  Those who wish to obtain more detail of the Nature
articles should contact me.

Best wishes
 

David Duthie
 

**************************************************************

World's Soils Can Store Carbon to Benefit the Environment Finds Paper
by the Council for Agricultural Science and Technology

The same farming practices that promote soil conservation can also
decrease the amount of CO2 accumulating in the atmosphere and threatening
a global warming, according to a new issue paper by the Council for
Agricultural Science and Technology (CAST). Agricultural practices that
conserve soil and increase productivity while improving soil quality also
increase the amount of carbon-rich organic matter in soils,
therebyproviding a global depository for CO2 drawn from the atmosphere by
growing plants.

"We call it a win-win. Returning carbon to the soil in the form of
organic matter is good agronomy. On farmed land, carbon has been released
through practices that promoted organic matter oxidation, but it can be
restored. An even greater opportunity for carbon storage lies in the some
2 billion hectares of desertified and degraded lands worldwide (75% in the
tropics) where improved land management could benefit soil quality and
hold carbon.

A significant fraction of the 30% increase in atmospheric CO2 over the
past 150 years stems from the breakdown of soil organic matter after
forests and grasslands were cleared for farming. So there is room for
it to go back," says Norman J. Rosenberg who authored the paper along with
R. Cesar Izaurralde.

There are opportunities to store carbon in soils around the world,
according to Izaurralde. The soil's storage capacity for carbon has
limits, but sequestration of carbon in soils offers a unique strategic
opportunity to slow global warming especially in the next 30 to 40
years while new, energy-efficient low-carbon power generation and
transportation technologies are phased into use.

The CAST paper highlights results of a workshop organized by the
Department of Energy's Pacific Northwest and Oak Ridge National
Laboratories in conjunction with CAST. Nearly 100 Canadian and U.S.
scientists, agricultural representatives, policy makers, and others
attended the workshop. New scientific opportunities were identified at the
workshop to increase both the content and duration of carbon in soils. The
need for inexpensive instruments and other ways of monitoring changes in
soil carbon also was recognized. Workshop participants also discussed the
question of what would encourage farmers to adopt practices that lead
to increased soil carbon storage.

The paper indicates that there are also energy costs associated with
capturing carbon in the soil -- through the production, transport, and
application of chemical fertilizers, manures, and pesticides; as well
as the pumping and delivery of irrigation water needed to increase plant
growth. But because these costs are primarily connected to food and fiber
production, the resulting increase in soil carbon storage might decrease
or even offset the net contribution of agriculture to global warming.

CAST is an international consortium of 38 scientific and professional
societies. Its mission is to identify food and fiber, environmental,
and other agricultural issues and to interpret related scientific research
information for legislators, regulators, and the media for use in public
policy decision making. More information on CAST and its numerous
scientific reports are available at http://www.cast-science.org. Copies of
the reports, including Storing Carbon in Agricultural Soils to Help
Mitigate Global Warming, are available from CAST at (515) 292-2152 or by
e-mail at cast@cast-science.org.

Contact: Norman J. Rosenberg, phone (202) 646-5029,
nj.rosenberg@pnl.gov;
R. Cesar Izaurralde, phone (202) 646-5227, cesar.izaurralde@pnl.gov;
Richard E. Stuckey, phone (515) 292-2125, rstuckey@cast-science.org; or
Karen Coble Edwards, phone (703) 502-8980, karen@kcegroup.com

***********************************************************************************
STUDIES CAST DOUBT ON CARBON SEQUESTRATION IN TREES

 WASHINGTON, DC, May 24, 2001 (ENS) - Two studies released today raise
questions about how much the planting of trees could reduce the effects of
global warming.

 Policy makers are searching for ways to reduce atmospheric levels of
carbon dioxide (CO2). One suggested way is to lock up some of the extra gas
in growing wood, or in the soil created by microbes from fallen vegetation.

 Some earlier experiments had suggested that the extra atmospheric carbon
dioxide might itself have a fertilizing effect on forests, causing them to
lock up extra amounts of CO2 and thus mitigate global warming impacts.

 But results from continuing experiments near Duke University - where
forest plots grow in the higher atmospheric levels of carbon dioxide
expected by the mid 21st century - suggest that trees and soil may not sop
up much of the extra gas over the long term under real world conditions.

 The two articles, published in today's issue of the journal "Nature,"
shows that while 20 year old loblolly pine trees began growing up to about
25 percent more wood after becoming exposed to 1.5 times current levels of
CO2, that initial growth spurt dropped back to only marginal gains after
the first three years.

 Researchers found they were able to enhance wood production as much as 74
percent at a nearby experimental site by providing extra nitrogen
fertilizer as well as CO2 to trees growing in nutrient poor soils. But
growth did not increase at all without the supplemental nitrogen.

 "When we exposed trees in low nutrient soil to elevated CO2, they
maintained growth increases only with added nutrients," said co-principal
investigator David Ellsworth, assistant professor of plant physiological
ecology in the School of Natural Resources and Environment at the
University of Michigan. "While CO2 initially acts as a stimulus to the
tree's physiology, our experiments suggest that short term increases in
growth are not sustainable over the long term in low nutrient
environments."

 "That suggests that CO2 effects on tree growth in pine forests will be
highly variable and depend greatly on site fertility, perhaps to the point
of not responding at all on the nutritionally poorest sites," concluded the
article's 11 authors, led by Ram Oren, an associate professor at Duke's
Nicholas School of the Environment and Earth Sciences.

*********************

SCHLESINGER, WILLIAM H. AND JOHN LICHTER (2001) Limited carbon storage in
soil and litter of experimental forest plots under increased atmospheric
CO2. Nature 411: 466-469.

Abstract: The current rise in atmospheric CO2 concentration is thought to
be mitigated in part by carbon sequestration within forest ecosystems,
where carbon can be stored in vegetation or soils. The storage of carbon in
soils is determined by the fraction that is sequestered in persistent
organic materials, such as humus. In experimental forest plots of loblolly
pine (Pinus taeda) exposed to high CO2 concentrations, nearly half of the
carbon uptake is allocated to short-lived tissues, largely foliage. These
tissues fall to the ground and decompose, normally contributing only a
small portion of their carbon content to refractory soil humic materials.
Such findings call into question the role of soils as long-term carbon
sinks, and show the need for a better understanding of carbon cycling in
forest soils. Here we report a significant accumulation of carbon in the
litter layer of experimental forest plots after three years of growth at
increased CO2 concentrations (565 µl l-1). But fast turnover times of
organic carbon in the litter layer (of about three years) appear to
constrain the potential size of this carbon sink. Given the observation
that carbon accumulation in the deeper mineral soil layers was absent, we
suggest that significant, long-term net carbon sequestration in forest
soils is unlikely.

**********************************
OREN RAM , DAVID S. ELLSWORTH, KURT H. JOHNSEN,NATHAN PHILLIPS, BRENT E.
EWERS, CHRIS MAIER,KARINA V.R. SCHÄFER, HEATHER MCCARTHY,GEORGE HENDREY,
STEVEN G. MCNULTY &GABRIEL G. KATUL (2001) Soil fertility limits carbon
sequestration by forest ecosystems in a CO2-enriched atmosphere. Nature
411: 469-472

Abstract:  Northern mid-latitude forests are a large terrestrial carbon
sink. Ignoring nutrient limitations, large increases in carbon
sequestration from carbon dioxide (CO2) fertilization are expected in these
forests. Yet, forests are usually relegated to sites of moderate to poor
fertility, where tree growth is often limited by nutrient supply, in
particular nitrogen. Here we present evidence that estimates of increases
in carbon sequestration of forests, which is expected to partially
compensate for increasing CO2 in the atmosphere, are unduly optimistic. In
two forest experiments on maturing pines exposed to elevated atmospheric
CO2, the CO2-induced biomass carbon increment without added nutrients was
undetectable at a nutritionally poor site, and the stimulation at a
nutritionally moderate site was transient, stabilizing at a marginal gain
after three years. However, a large synergistic gain from higher CO2 and
nutrients was detected with nutrients added. This gain was even larger at
the poor site (threefold higher than the expected additive effect) than at
the moderate site (twofold higher). Thus, fertility can restrain the
response of wood carbon sequestration to increased atmospheric CO2.
Assessment of future carbon sequestration should consider the limitations
imposed by soil fertility, as well as interactions with nitrogen
deposition.

Dr David Duthie
UNEP/GEF Biodiversity Enabling Activities
PO Box 30552
Gigiri, Nairobi
KENYA

Tel: +254-2-623717
Fax: +254-2-624868
E-mail: david.duthie@unep.org

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