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NCEAS Study
updated: Jan 04, 2012, 2:37 PM
Source: UCSB
A recent study conducted by a working group at UC Santa Barbara's National
Center for Ecological Analysis and Synthesis (NCEAS) suggests that climate
change predicted for the United States will boost demand for imported drought-
and heat-tolerant landscaping plants from Africa and the Middle East. This
greatly increases the risk that a new wave of invasive species will overrun
native ecosystems in the way kudzu, Oriental bittersweet, and purple loosestrife
have in the past, the international team of scientists says.
The kudzu invasion of the past few decades saw whole forests overgrown in the
Southeast, along with hedgerows, power lines, and even houses. In wetlands
across the nation, purple loosestrife is crowding out native marsh plants; and
Oriental bittersweet, if left unchecked, shades and chokes out native trees,
bushes, and shrubs along streams, forests, and field edges.
The scientists recommend that U.S. authorities adopt proactive management
practices, in particular pre-emptive screening of nursery stock before new
plants are imported, to prevent such an explosion of new invasives. Their
conclusions appear in an early online edition of the Feb. 1 issue of the journal
Frontiers in Ecology and the Environment.
As lead author Bethany Bradley of the University of Massachusetts Amherst
explains, the U.S. Department of Agriculture (USDA) has proposed the Not
Authorized Pending Pest Risk Analysis rule to regulate the industry. The rule
would require importers to notify the USDA of proposed imports. USDA scientists
would then conduct a timely risk assessment and issue a recommendation to allow
or curtail the imports.
"Our study identifies climate change as a risk, which, combined with other
factors, is likely to increase demand for imported heat- and drought-tolerant
plants, but this emerging threat is one that policy can effectively address,"
Bradley says. "The USDA has tools to reduce import risk and we advocate that now
is the time to put them in place. Pre-import screening has been tested in
Australia for about 10 years now and it's not foolproof, but it seems to have
done a good job of separating the really bad import ideas from more benign
introductions."
Stephanie Hampton, deputy director of NCEAS, adds: "This research group has
undertaken a tough synthesis challenge: to anticipate invasion risk and identify
pragmatic precautions that could be taken. As climate changes, it alters not
only the environment that non-native species encounter, but also society's
demand for exotic imports."
Not all imported plants become invasive, but those that do can become a
significant threat to native plants and we should not be complacent about the
current situation, Bradley says. About 60 percent of plants now considered
invasive were introduced deliberately through the plant trade. The other 40
percent are human-related accidental introductions such as seeds stuck in cargo
or shipping containers. Only a tiny fraction of non-native introductions are
from natural causes such as blowing in with a hurricane, Bradley says.
She and colleagues point out that rising average temperatures in certain regions
of the U.S. are already shifting plant hardiness zones northward, and the trend
is expected to continue globally. Their study suggests that with the earlier
onset of spring, warmer winters, economic globalization, and increased trade
with emerging economies in Asia and Africa, we may face a significant new wave
of invasive plant introductions.
For this analysis of the intersection of global trade and climate change, the
ecologists used import values from 1989 to 2010 to identify emerging trade
partners, because earlier studies had established a clear link between increased
trade and the number of invasive species. They found 42 emerging trade partners
poised to supply new nursery plant varieties including Thailand, Egypt, Saudi
Arabia, Ecuador, Argentina, and several countries in equatorial Africa.
The rate of introduction is steepest in the early stages of new trade
relationships, the authors say. "Unfortunately, increasing the variety and
availability of non-native, drought-tolerant species could also increase the
probability of introducing species capable of invading dryland regions." Bradley
adds: "In the desert Southwest this has already been happening with xeriscaping,
which is becoming more and more popular." Xeriscaping refers to gardening with
low or no need for watering.
The scientists' work focuses on introduction, the first of three stages of
invasion, because "stopping invasions before they start is the most effective
way of preventing widespread ecological and economic impacts," Bradley says.
"Globalization has accelerated the rate of introduction from a few species at
the first colonization of North America to now, when we probably see thousands
of new species each year. All we need is another kudzu to have a big impact."
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