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Green Aliens Invade the US
© 1997, 1998 Streamline Publications
According to the U.S. Department of the
Interior, invasive nonnative plants are described as the second-most important
threat to native species after habitat destruction. Weeds have a far greater
negative effect on our lives than just being irritating intruders—flaws in
our perfect landscapes. They have become no less than an alien invasion bent on
destroying our environment and economy. The invaders have become an enemy within
and American citizens its willing accomplices. These invasive nonnative plants have
such a devastating effect because their natural controls are missing and some
can establish dominance in the absence of predators. Aggressive invaders
displace native species that may provide food and habitat for native animals.Foreign species were intentionally
introduced in the past with noble intentions. Florida is a particularly
instructive example having played willing host to hydrilla which now infests
over 75,000 acres of the state's waterways. Melaleuca, now a major threat to the
Everglades, was introduced in 1906 as an agricultural windbreak, soil stabilizer
and ornamental tree. Australian pine overruns the barrier islands endangering
sea turtle and American crocodile habitats. Many of these dangerous plants are
commercially available today in Florida and elsewhere.
A Worldwide ThreatOur globalized economy is part of the
problem with greater personal travel and increased cross-border commerce. The
problem is so threatening an all-out federal interagency government effort has
been launched to not only research and combat the invasion but to educate the
public and enlist cooperation of the states. The problem is not solely that of
the United States—nonnative weed problems affect the world's nations and
have been identified on every continent but Antarctica.
Of the thousands of alien plants
introduced to the U.S. fourteen hundred have been identified as pests and of
that number, ninety-four are recognized as noxious weeds. These invasive exotics
can have far-reaching impact on croplands, forests, parks, preserves, wilderness
areas, wildlife refuges and urban parklands. Expert estimates place the
infestation currently at over 100 million acres with an 8 to 20 percent increase
each year. Deputy Secretary of Agriculture Richard
Rominger calls the problem an economic and ecological threat that is a "...cancer
on our landscape."
Local Effects
In California's Sequoia National Park a
vegetation study has shown ninety-five percent of the herbaceous layer is made
up of introduced grasses and other herbs—in certain areas the nonnative
plants have totally taken over.According to an April, 1997 Interior
Department news release, in 1989, a single clump of a South African annual
composite (Osteospermum fruticosum) was found on Santa Cruz Island off the
Ventura County coast. The entire population was successfully removed. There has
been less success with other nonnative California invaders: Moroccan mustard,
iceplant and tree tobacco to name just a few. Of California's nearly 6,000 plants of
all kinds, nearly 18 percent have been introduced from elsewhere. Many, such as
Mediterranean grasses brought here by Spanish explorers and missionaries have
had hundreds of years to establish themselves.The Interior Department estimates that
noxious weeds are spreading to western wildlands at a rate of almost 5,000 acres
a day. The effects of invasive nonnative
plants can at times be bizarre. Saltcedar or tamarisk (Tamarix ramosissima) is
taking over many western riparian sites that have been disturbed by large-scale
changes in river systems such as dams and irrigation projects. The saltcedar's
leaves exude salts which increase salinity of the soil to a level native plants
cannot tolerate. Willows and cottonwoods along streams are displaced.
A High PriceNationwide, the bill farmers and
ranchers pay for weed control amounts to $5 billion annually. Lost productivity
of crops and rangeland exceeds $7 billion each year. These costs are fairly
easily quantifiable. But how can we determine the cost of an ecology that has
been changed forever?In the United States, introduced
invasive plants comprise from 8 to 47 percent of the total flora of most
states...
Read a fable about Mediterranean grasses and how they got here.
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