TIME: Almanac 1993/TIME Almanac 1993.iso/time/091090/0910340.000

Text File | 1992-08-28 | 3.9 KB | 85 lines

                                                                                NATURE, Page 75

Invasion of the Habitat Snatchers


Exotic plants and animals are ruining the nation's wilderness


    By the end of the year, well over 10 million people will
have traveled to America's national parks to see the few tiny
patches of land that are still as pristine as they were before
Columbus landed, or so most believe. In fact, the National Park
Service is coping with a growing problem that is partly
nature's doing but largely the result of civilization's subtle
intrusions. Far from being islands of primeval beauty, parks
from Hawaii to North Carolina are being overrun with nonnative
plants and animals, virtually all of them introduced,
inadvertently or on purpose, by man. These "exotic threats"
have become, officials say, the most serious danger facing the
323,750 sq. km (125,000 sq. mi.) national park system.

    The most dramatic threats are in Hawaii, where the 900
indigenous plant species -- some found nowhere else in the
world -- face new competition from another 900 species of
nonnative plants, including banana poka and ornamental ginger.
The banana poka was imported in the 1950s by a Japanese
gardener, and has since spread its vines over 16,200 hectares
(40,000 acres). Other exotics were introduced  in the 1930s in
an attempt to conserve water and stem soil erosion. Now
biologists fear a time when the native plants will be completely
gone from places like Haleakala National Park.

    Invading animals are also a difficult problem. Rats have
been hitching rides to the islands on ships for centuries, then
escaping into the forests where they feast on nesting birds and
their eggs. Local authorities imported mongooses to hunt the
rats in 1883. But no one considered that mongooses hunt in the
early morning and early evening, when the rats are not out. So
the mongooses switched to birds, compounding the problem.

    In Great Smoky Mountains National Park, the main culprits
are wild boars, descendants of animals imported to North
Carolina in 1912 for hunting. The boars weigh as much as 136
kg (300 lbs.), and, says park official Joe Abrell, "tear up
most everything in their paths." Man is responsible as well for
oriental bittersweet, a vine imported to control erosion. It
is strangling trees. Says park resource specialist Keith
Langdon: "Once it gets a grasp on the land, it doesn't
relinquish it."

    Another plant is overrunning parts of the Southwest,
including the Grand Canyon. Introduced about 70 years ago to
act as an erosion fighter and windbreak, the tamarisk tree has
taken over about 81,000 hectares (200,000 acres), pushing out
native trees and threatening eight species of birds that nest
in them. The Grand Canyon's major animal offenders are burros;
turned loose by prospectors generations ago, they have grown
into vegetation-devouring herds.

    Large animals can be either killed or removed, but that
sometimes causes problems of another sort: a burro-shooting
program at the Grand Canyon had to be halted after a public
outcry. In Hawaii Volcanoes National Park, though, a population
of 15,000 or so feral goats was reduced to only 4, and in the
Smokies the wild boar population has been pared. Smaller
animals are much harder to fight, and plants harder still.
Herbicides kill too indiscriminately, and bringing in new
exotic species to control the old is demonstrably dangerous.
Rangers often have to resort to chopping down or uprooting
invading plants one by one, a holding action at best. In the
end, park officials -- and visitors -- will have to accept that
the nation's wild lands will never return to their original
state. The best that can be done is to work hard to keep new
exotic threats from following on the heels of the old.


By Michael D. Lemonick. Reported by Scott Brown/Hilo and Michael
Mason/Atlanta.