In this issue:
Where Did They Come From?
How Did They Get Here?
By Libby Campbell
Invasive alien plants came here either accidentally
or deliberately. The accidentals include Japanese stilt grass, 
which
was used as packing material for shipments from Asia. Seeds escaped when the
boxes were opened, and this tough grass found no natural predators. Even deer
won't eat it. Consequently it spreads rapidly in over-grazed areas where deer
have eaten the more palatable native grasses. Many other alien invasives have
arrived by unintentional "hitchhiking" through international trade,
with exotics stowing away in ships, planes, trucks, and shipping containers,
or arriving on nursery stock, unprocessed logs, fruits, seeds, and vegetables.
Deliberate introductions were either for ornamental
or practical reasons. Gardeners constantly search for beautiful new species
to plant, and this often means an exotic plant from a similar but distant
biome. Of course, they do not want the insects or diseases that keep the plant
in check in its native habitat. Also, gardeners are seduced by descriptions
such as "hardy", "fast growing", and "care-free."
This is a perfect description of an exotic introduction that will escape the
cultivated confines of the garden and out-compete native flora. Examples of
beauties that have exceeded their welcome are wisteria (introduced in the
early 1800's), Princess Tree or Paulownia (imported in the 1840"s), Oriental
bittersweet (introduced in the 1860's), and Tree of Heaven or Ailanthus (imported
in 1784.)
Some introductions have been for very good reasons.
Kudzu was introduced into the U.S. in 1876 at the Philadelphia Centennial
Exposition, where it was promoted as a forage crop and an ornamental plant.
From 1935 to 
the
mid-1950s, farmers in the south were encouraged to plant kudzu to reduce soil
erosion, and Franklin D. Roosevelt's Civilian Conservation Corps planted it
widely for many years. Chinese lespedeza was introduced by federal and state
agencies for bank stabilization, soil improvement, wildlife and forage and
cover, and hay. Multiflora rose was introduced in 1866 as rootstock for ornamental
roses. Beginning in the 1930s, the U.S. Soil Conservation Service promoted
it for use in erosion control and as "living fences" to confine
livestock. State conservation departments soon discovered value in multiflora
rose as wildlife cover for pheasant, bobwhite quail, and cottontail rabbit
and as food for songbirds and encouraged its use by distributing rooted cuttings
to landowners free of charge. More recently, multiflora rose has been planted
in highway median strips to serve as crash barriers and to reduce automobile
headlight glare. Russian olive, first cultivated in Germany in 1736, was introduced
into the U.S. in the late 1800s, and was planted as an ornamental. Until recently,
the U.S. Soil Conservation Service recommended Russian olive for wildlife
planting and windbreaks. Though highly useful for these purposes, the exotic
plants have spread widely and dominate large areas formerly populated by a
wide variety of native species, greatly reducing biodiversity.
An important source of alien introductions has
been for food. Nearly all of our agricultural crops, with the notable exceptions
of corn, beans and squash (the Native Americans' Three Sisters), are originally
from E
urope,
Africa or Asia. Even the dandelion, so widespread as to be thought native
by most Americans, came from Europe with early colonists as a salad plant.
However, we do not see corn growing aggressively in our abandoned fields or
waysides. Only a few have escaped and become serious problems, most notably
herbs such as Beefsteak plant from Asia, and garlic mustard from Europe. Livestock
will not eat them, and pastures gradually lose valuable grazing space as these
aliens take over.
Plants, like people or any species, are appreciated
when they add beauty and grace, and are willing to peacefully coexist. A newcomer
who takes over, drives out the natives, and dominates the landscape has worn
out its welcome.
Above: Japanese Honeysuckle
Above left: Japanese Barberry
Oriental
Bittersweet
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