Introductions All Around

Humans have always carried plants and animals with them as they move around the world. In some cases, these introductions were accidental. The destructive Japanese beetle came from Asia hidden in the soil of nursery plants. Many other times, though, the arrival of an exotic species was intentional--domestic animals and food crops among the most common.

The majority of plant introductions to North America have been relatively harmless, and are well adapted to the uses we make of them in our landscapes. The turf grasses are a good example of this. Bluegrass, ryegrass, and tall fescues are all European or Asian natives. On the East Coast, they do well in sunny open lawns. If the natural forest cover were to return, they would die out due to shading. Fescue in the plains, though, is of concern because it overtakes natural grasslands. It crowds out the many species of native grasses that provide superior forage for wildlife and livestock.

There is a stretch of Interstate 95 in Cecil County, Maryland, and another on U.S. Route 1 in Harford County that has dozens of huge clumps of miscanthus grass, a native of eastern Asia. Miscanthus cultivars became all the rage as landscape plants starting about 15 years ago. Now the seeds have escaped and colonized unintended sites. Environmentalists caution against introducing miscanthus near natural areas.

Dr. Ann Rhoads of the Morris Arboretum in Philadelphia found that over a third of the plants growing wild in Pennsylvania today were not present before European settlers arrived. There are other reports that from 12 to 37% of the species in the Northeast and Midwestern states are not native.

Native can be narrowly or broadly defined, and everything in between. This is often because of the artificial boundaries we've drawn. A good example of this is the Baldcypress. In the broadest sense, Baldcypress is native to North America--but not Canada. We could also say it is native from Louisiana up to Arkansas, southern Illinois and Missouri, and eastward to Delaware and Florida. To narrow the definition even more, it is native to Sussex County, DE, but not Kent or New Castle Counties. Baldcypress is adaptable and has been successfully introduced as a landscape plant well beyond its natural range, even into Canada.

Human disruption of the environment has tipped the balance to allow invasions of non-native plants in other ways. Loss of open spaces combined with ready food from farm fields has resulted in an explosion in the whitetail deer populations, concentrated into smaller areas. As deer move through open woods, they browse mostly on the native plants, while avoiding the non-natives they did not evolve with and develop a taste for. This gives the invaders even more sun, water, and soil nutrients to fuel their advance.

Some species have become so widespread that it is impossible to reduce their spread or persistence in areas they already inhabit. Organizations such as The Nature Conservancy and USDA encourage extra vigilance to prevent new introductions and escapes, and to funnel resources into identifying and stopping invasives before they become too widespread.

Master Gardener volunteers can answer your home lawn, garden and pest questions on The Garden Line. Master Gardeners are also offering a number of home lawn and garden workshops this spring. Email garden-line@udel.edu or phone 302-831-COOP for more information.

—Jo Mercer, Extension Educator, Horticulture & Environmental Science
Originally published in “Newark Outlook,” The Newark Post

Copyright © 1997-2002 NCC Cooperative Extension. Last revised July 23, 2003.