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January 27, 2009
A new study by researchers at
Princeton University’s
Woodrow Wilson School of Public and International Affairs has
found that global climate change may lead to the retreat of some
invasive plant species in the western United States, which could
create unprecedented ecological restoration opportunities across
millions of acres throughout America. At the same time, global
warming may enable other invasive plants to spread more widely.
The study, “Climate change and plant invasions: restoration
opportunities ahead?”, was co-authored by Bethany Bradley, a
biogeographer, Michael Oppenheimer, a geoscientist, and David
Wilcove, a conservation biologist, at Princeton’s Woodrow Wilson
School, and will soon be published in the journal
Global Change Biology.
The researchers assessed the relationship between climate change
and the distribution of five prominent invasive plants in the
western United States – known colloquially as the “kudzus of the
West” – cheatgrass; spotted knapweed; yellow starthistle;
tamarisk; and leafy spurge. Such plants are defined as invasive
because they were brought into this country from other lands and
now dominate and alter ecosystems in ways that threaten native
wildlife, agriculture, and ranching. All have greatly expanded
their ranges in recent decades in the western U.S., causing
millions of dollars in damage to farmlands and rangelands.
Invasive plants are increasingly expensive to control, and it is
widely believed that global warming will make the problem worse.
But Bradley and her co-authors find that global warming may also
reduce the competitiveness of some invasive plants if conditions
become climatically unsuitable to the weeds, “creating
opportunities for restoration in areas currently dominated by
intractable invasive species,” according to the study.
The five species were selected in part because they represent
the most problematic plants in the western U.S. The study
authors created “bioclimatic envelope models,” wherein the
authors identified where the invasive plant species occurred,
and identified critical climate variables such as precipitation
patterns and temperature patterns that are associated with the
presence of the invasive plants under investigation. The authors
then determined what combined set of climate variables best
described the distribution of these weeds, and mapped all of the
places in the U.S. where these climate conditions occur.
Developing such models is important because scientists can use
them to assess how changing climate conditions might affect the
distributions of invasive plants. Maps of how invasion risk is
likely to change with global warming are also important for land
managers designing long-term protocols for fighting invasive
plants.
The researchers employed 10 atmosphere-ocean general circulation
models (AOGCMs) that predict what climatic conditions in the
West are likely to be in 2100 if emissions are not limited, and
matched those predicted conditions to the climate conditions
associated with each of the invasive plant species. The
projected invasive species distributions for each of the models
were added together to create a map of invasion risk under
future climate conditions.
“Just as native species are expected to shift in range and
relative competiveness with climate change,” the authors wrote,
“the same should be expected of invasive species.”
Specifically, the researchers concluded that climate change is
likely to expand invasion risk from yellow starthistle in
California and Nevada – and lands currently occupied by invasive
populations of the weed in California, Oregon and Washington are
unlikely to become unsuitable for the species; hence, they have
low potential for restoration. Tamarisk distribution, they
found, is unlikely to be affected by climate change.
Cheatgrass, however, is likely to be affected by climate change,
potentially moving northwards into parts of Idaho, Montana and
Wyoming, but retreating in southern Nevada and Utah. And,
according to Bradley and her co-authors, the impacts of climate
change will likely shift spotted knapweed, currently distributed
throughout the foothills of the Rocky Mountains and the Colorado
Plateau, to higher elevations, leading to both expanded risk and
restoration opportunities in part of Montana, Wyoming, Utah, and
Colorado.
Leafy spurge, abundant in northern states west of the
Mississippi River and some rangeland west of the Rockies, will
likely retreat from some places in the face of climate change,
creating restoration possibilities in Colorado, Nebraska, Iowa,
and Minnesota – but potentially expanding into parts of Canada
not included in the researchers’ study. In addition, the
researchers found that leafy spurge is likely to retreat from
Nebraska and parts of Oregon and Iowa, creating strong potential
for restoration in these areas.
To better address the impacts of invasive species, the authors
note, further modeling and experimental work is needed to
determine which species will be able to occupy these sites if
the invasive species are reduced or eliminated by climate
change. Local native plants (the ones that were there prior to
the arrival of the invasive species) may be unable to reoccupy
these areas as a result of global warming. If local native
plants cannot reoccupy the areas, then native plants from
elsewhere in the West will need to be considered for restoration
to prevent new invasive species from quickly invading these
sites.
“The restoration opportunities associated with the retreat of
currently intractable invasive species are vast in the western
United States,” the authors wrote. “The uncertainties associated
with these changes, as well as the unknown makeup of viable
future vegetation… highlight a pressing need for integrated
modeling, monitoring, and experimental work to better address
the ecological consequences of climate change.”
“The question for policy makers and land managers is, ‘What do
we want these lands to be?’” said Wilcove. “These lands will
change, and we must decide now – before the window of
opportunity closes - whether we do nothing or whether we
intervene.”
“Governments need to reduce emissions quickly to avoid a variety
of dangerous climate changes, Oppenheimer warned. “At the same
time, it will be necessary to adapt to the inevitability of some
warming. Proper management of ecosystems to minimize the damages
is a key part of any effective adaptation strategy.”
Source: Wiley - Blackwell
Climate change and plant
invasions: restoration opportunities ahead?
Bradley B.A., Oppenheimer M., Wilcove D.S.,
Global Change Biology, 2009, DOI:
10.1111/j.1365-2486.2008.01824.x
ABSTRACT
Rather than simply
enhancing invasion risk, climate change may also reduce
invasive plant competitiveness if conditions become
climatically unsuitable. Using bioclimatic envelope
modeling, we show that climate change could result in both
range expansion and contraction for five widespread and
dominant invasive plants in the western United States.
Yellow starthistle (Centaurea solstitialis) and tamarisk
(Tamarix spp.) are likely to expand with climate change.
Cheatgrass (Bromus tectorum) and spotted knapweed (Centaurea
biebersteinii) are likely to shift in range, leading to both
expansion and contraction. Leafy spurge (Euphorbia esula) is
likely to contract. The retreat of once-intractable invasive
species could create restoration opportunities across
millions of hectares. Identifying and establishing native or
novel species in places where invasive species contract will
pose a considerable challenge for ecologists and land
managers. This challenge must be addressed before other
undesirable species invade and eliminate restoration
opportunities.
Source:
http://www3.interscience.wiley.com/journal/121521769/abstract.
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