![Photo: Leafy spurge. Link to photo information](https://webarchive.library.unt.edu/eot2008/20090508085401im_/http://www.ars.usda.gov/is/graphics/photos/nov01/k2601-1i.jpg) Global change is likely to
exacerbate invasion and spread of exotic plants like leafy spurge, which
already costs millions of dollars to control each year.Click the image for
more information about it. |
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Why Invasive Plants Take Over
By Don Comis
April 30, 2009
New research shows that two key causes of plant invasion--escape from
natural enemies, and increases in plant resources--act in concert. This result
helps to explain the dramatic invasions by exotic plants occurring worldwide.
It also indicates that global change is likely to exacerbate invasion by exotic
plants.
Agricultural Research Service
(ARS) ecologist
Dana
Blumenthal reached these conclusions after studying 243 European plant
species and their fungal and viral pests, both in Europe and in the United
States.
The
study was published this week in the Proceedings of the National Academy of
Sciences.
Blumenthal, based at the
ARS
Rangeland Resources Research Unit in Fort Collins, Colo., and colleagues at
the University of North Carolina and in the
Czech Republic showed that fast-growing
plant species adapted to moist, nitrogen-rich soils had many fungal and viral
pathogens in the areas where the weedy species evolved. Once these species
arrived here, they escaped many of their long-time enemies.
Such an escape from numerous enemies is thought to provide exotic
species with an advantage over native species still burdened by their enemies.
This is the first study, however, to show that whether a plant escapes from a
few or an unusually larger number of enemies can be predicted from the type of
plant: Exotic species that are fast-growing and weedy are likely to have more
enemies to escape from.
Unfortunately, these are the same species most favored by global
change. Fast-growing weedy species thrive in environments with ample plant
resources. And global change increases key plant resources, such as carbon
dioxide and soil nitrogen, through increases in the greenhouse gases carbon
dioxide and nitrous oxide, respectively.
Fast-growing, weedy exotic species therefore have a double advantage
in today's world. Increases in resources enable them to outcompete slow-growing
plants. An escape from an unusually large number of enemies enables them to
outcompete even fast-growing native plants. As global change proceeds,
continuing increases in resource availability are likely to exacerbate such
plant invasions.
The National Science Foundation, the
European Union, and the Czech
Republic supported the study.
ARS is the principal intramural scientific research agency in the
U.S. Department of Agriculture.