Will a warmer climate make plants more prone to spring freezes?
(Photo by Carlye Calvin.) An analysis of an April 2007 freeze that devastated
crops and forests across the mid-South warns
of the risk of more such events as climate change
unfolds and the potential variability of
springtime temperatures goes up.
According to the
authors of the study, published in the March
2008 issue of BioScience, “Plant
ecologists have long been concerned with
a seemingly paradoxical scenario in the relationship
between plant growth and climate change:
warming may actually increase the risk of plant
frost damage.” The
study was led by Lianhong Gu (Oak Ridge National
Laboratory).
Temperatures dipped well below
freezing from Missouri to the mid-Atlantic
during the period of 5–9 April after a long
stretch of unusually warm weather. At the Missouri
Ozark AmeriFlux site, nighttime readings stayed
above 15°C (59°F)
for a full week before the freeze, then dipped
as low as –7°C (19°F). The early
warmth pushed plant growth two weeks ahead
of schedule in many areas, intensifying the
effects of the subsequent freeze.
More than $100
million in damage was reported in North Carolina
alone, and the effects on many crops and
trees persisted through the summer—a
sharp contrast to 1996, when a consistently
cold spring delayed greening but had less
impact on the year’s total plant growth.
Unusual damage patterns resulted from the asymmetric
nature of the 2007 freeze. For example,
the tops of forest canopies were
denuded, stimulating growth closer to ground
level, and trees near lakes and rivers were partially
protected by the relative warmth emanating from
those waters. The authors noted the role of the
freeze’s damage in
reducing regional carbon uptake: “All signs
have so far indicated that the 2007
spring freeze had at least a short-term, profound
effect on the terrestrial carbon cycle in much
of the central and eastern United States.”
Along
with generating climatic uncertainty,
greenhouse gases may also set up plants for freeze
damage in another way. According to the study, “There
is a mounting consensus that, for
many plant species, growth under elevated CO2
can reduce their resistance and tolerance to
freezing temperatures.” A
drop in stomatal conductance induced
by the extra CO2 appears to reduce plants’ ability
to acclimate to lower temperatures.
Oak Ridge National Laboratory
University of Missouri in Columbia
NASA
Six-year
assessment finds pollution plaguing national
parks
(Photo courtesy U.S. National Park Service.) Dozens of toxic compounds have invaded some
of America’s most-loved national parks,
designed to be sanctuaries from the industrialized
world. Over a six-year period, the Western
Airborne Contaminants Assessment Project
(WACAP)—the largest such study to date
outside of developed areas—sampled
snow, water, vegetation, lake sediment, and
fish at 20 national parks in Alaska, California,
Colorado, Montana, New Mexico, Oregon, Texas,
Washington, and Wyoming. The results were
released on 26 February.
Of the 100 contaminants tested for, the
study found evidence of 70, including long-banned
compounds such as DDT (dichloro-diphenyl-trichloroethane)
as well as still-legal pollutants such
as mercury and PCBs (polychlorinated biphenyls).
The focus of the study was on semi-volatile
organic compounds and heavy metals.
Along with studying the parks’ ecosystems,
researchers traced prevailing winds to
determine likely sources of pollutants.
Many long-lived pollutants appear to
have reached the parks from as far away
as Asia, especially for mountainous parks,
whose high terrain intercepts globe-circling
jet streams. However, even pesticides
with short atmospheric lifetimes affected
some parks located near high-intensity
agricultural areas.
Results from the project add considerably
to the state
of the science on contaminant transport
and subsequent biological and ecological
effects on remote ecosystems in the
western United States. “These
well-documented
and carefully analyzed data will provide
a basis for evaluating future changes
in the status of these ecosystems,” says
WACAP scientific director Dixon Landers
(U.S. Environmental Protection Agency).
The
core study area
included eight national park areas:
Glacier, Mount Rainier, Olympic, Rocky
Mountain, Sequoia and Kings Canyon,
Denali, Gates of the Arctic, and Noatak.
The study was funded primarily by the
National Park Service (NPS). Principal
investigators included scientists from
NPS, EPA, the U.S. Geological Survey,
the Forest Service, and the universities
of Oregon State and Washington.
www.nature.nps.gov/air/studies/air_toxics/wacap.cfm
U.S.
National Park Service
U.S.
Forest Service
U.S. Geological
Survey
Oregon
State University
U.S. Environmental
Protection Agency
University
of Washington
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