international trade could be death knell to many of our native
species, says UC Berkeley ecologist
Robert Sanders, Public Affairs
D.C. - While the booming global economy promises greater prosperity
in the next century, it poses a real threat to the country's
native plants and animals as well as to its productive croplands,
says an ecologist from the University of California, Berkeley.
trade has a really big cost associated with it," said Carla
M. D'Antonio, associate professor of integrative biology and
an expert on invasive plants. "Most harmful non-indigenous
insect pests and plant pathogens arrive in the U.S. as stowaways
on nursery stock, raw logs or cargo containers. And many invasive
exotic plants are purposely introduced through the horticultural
invaders already cost the country $136 billion every year in
lost and damaged products and the expense of controlling them,
according to a January article in the journal Bioscience. With
a predicted exponential rise in international trade, D'Antonio
predicts at least a 50 percent rise in this cost in the next
20 years, not including any increased costs from battling invaders
already established in this country.
obviously can't get rid of trade, but we have to make a commitment
to inspection, quarantine and control to accompany the rise
- and that is just to maintain things as they are today,"
she said. "The first place to stop these exotic species
is at the dock, or even better, before they leave their native
will lay out her predictions in a talk on Sunday, Feb. 20, at
this week's meeting of the American Association for the Advancement
of Science in Washington, D.C., at a session on "Ecological
Forecasting: How Will Human Domination Impact Ecosystems This
estimates that some 1,500 new insects and 50 new pathogens -
fungi or bacteria - will make their way into the United States
in the next 20 years, with perhaps 15 percent causing serious
ecological and/or economic harm.
economic effects come primarily from invaders, like the Russian
wheat aphid, that attack crops; parasitic plants like witch
weed, which now affect corn farmers; or weeds, such as thistles,
that invade cropland. Alien weeds like spotted knapweed, star
thistle and cheat grass reduce the quality of rangeland for
grazing cattle, while fungi and insects plague both croplands
and forest trees. A recent arrival is the Asian long-horned
beetle, first detected only in the past three years, now feasting
on hardwood trees in the Northeast.
beetle came over from China in wood packaging material and is
destroying street trees in several cities in the East,"
she said. "It has a very wide host range and, while it
is currently feasting on a variety of maple species, it has
the potential to expand to many other types of trees."
weeds accounted for $26 billion in loss and control last year,
while agricultural pests cost the country $14.4 billion, according
to the report in Bioscience. Forest pests, on the other hand,
cost $2.1 billion, counting control costs and lost production.
Fire ants alone accounted for a billion dollars last year in
control costs and the loss of rangeland in the Southeast and
from economic damage, however, these invaders upset the ecosystem,
preying on native species, outcompeting them and spreading disease.
They also can alter ecosystem processes to the point that the
systems can no longer support native species. Non-indigenous
species are second only to land use change in causing species
extinction, D'Antonio said.
don't think any native communities are entirely resistant to
invasion," she said. "With repeated introduction of
new propagules, you increase the probability that a few of them
will establish themselves, and eventually some will cause the
extinction of native species."
are larvae, seeds or pieces of plants or fungi capable of developing
into mature adults.
of the major sources of alien pathogens such as fungi are nursery
plants imported for the horticultural market. These come into
the country carrying foreign contaminants in the soil around
their roots or in the roots themselves. Though all nursery stock
must be quarantined and irradiated, this is not sufficient to
prevent the entry of many harmful pathogens, D'Antonio said.
stock has really been bad news for U.S. forests," she said.
U.S. Department of Agriculture's Animal and Plant Health Inspection
Service (APHIS) is responsible for inspecting all imports for
hitchhiking invaders, but huge container ships are difficult
to inspect thoroughly. And some imports, such as seeds, are
immune from inspection. More than 100,000 different seeds are
involved in the uncontrolled seed trade today, with at least
59,000 species available in U.S. seed catalogs alone, she said.
addition, many species introduced as ornamentals have become
highly invasive and ecologically damaging plants. These range
from kudzu and the tree melaleuca in the South to giant reed
grass and saltcedar in the West and Japanese honeysuckle in
the USDA is now studying its future needs, partly as a result
of President Clinton's decree several years ago to do everything
possible to control the introduction of new species, it is unclear
whether APHIS can keep up with the increase in imports.
inspection and quarantine and eradication efforts must be commensurate
with the increase in trade," D'Antonio said.
specialty is invasive plants in the Western U.S. and Hawaii.
Among the plants she has studied are ice plant, a South African
succulent that invades dune and shrub communities in coastal
areas; French broom, an abundant invasive shrub along the Pacific
coast; African pasture grasses that have invaded Hawaiian dry
forests and caused their almost complete demise; and grasses
introduced long ago, such as velvet grass, canary grass and
tall fescue, that force out native bunch grasses in the continental
U.S. Of primary interest are the ways through which exotic plants
outcompete native plants.
of her current new concerns is African buffel grass, planted
by Mexican cattle ranchers and now invading desert areas in
plant has the potential to enhance the occurrence of fire -
a disturbance to which the native species are not adapted,"