Preventing Plant Invasions

By Janet Marinelli
AS THE OLD saying goes, an ounce of prevention is worth a pound of cure. This is especially true of the struggle to control invasive species.

In the New York metropolitan area, where I live, roadsides have been overtaken by solid stands of purple loosestrife, and forest understories are thick with Japanese barberry.

Biologists consider invasive species such as these to be one of the two greatest threats to native plants and animals, second only to the outright loss of habitat to suburban sprawl, agriculture, and industrial development. Land managers fight a daily battle to remove invasives from important natural areas.

The conventional wisdom, at least in horticultural circles, used to be that most invasive plants were introduced accidentally—in agricultural seed stocks, say, or even on the bottom of some unsuspecting tourist’s shoes.

But during the course of researching Brooklyn Botanic Garden’s influential 1996 handbook Invasive Plants: Weeds of the Global Garden, my colleagues and I were dismayed to discover that about half of the worst invasive plants currently degrading natural habitats from coast to coast were brought here intentionally, for horticultural use.

While the vast majority of species planted on highway rights-of-way, in public landscapes, and in home gardens are not invasive, a small percentage have adapted too well and escaped cultivation. These plants have become established, or naturalized, in the wild.

Not every naturalized plant is a threat to native ecosystems, however. The BBG handbook Native Alternatives to Invasive Plants is concerned with those nonnative plants that not only establish viable populations in but also alter the structure and/or functioning of those ecosystems.

Many invasive plants are still being sold as garden specimens or for wildlife plantings and erosion control, despite their documented ability to degrade natural areas. And although no system is in place to effectively screen them for potential invasiveness, new plants from around the world are constantly being introduced to satisfy the preoccupation with the new and exotic that has characterized horticulture for at least the past hundred years.

The more we learn about invasive plants, the more we realize how difficult they are to control, much less eradicate. The most prudent course of action clearly is to avoid planting these species in the first place.

Since BBG’s original handbook on invasive plants was published, we have received numerous requests for a companion volume featuring ecologically safe alternatives. The Encyclopedia of Native Alternatives to Invasive Plants, at the heart of this book, recommends a variety of beautiful, regionally native species that fill the same needs as the worst nonnative invasive plants commonly used in horticulture.

If you select these species, it is highly unlikely that you will be unleashing North America’s next invasive menace. Regional natives aren’t the only ecologically responsible choices; nonnatives that have been planted in gardens for decades without demonstrating any signs of invasiveness are good candidates for landscaping as well.

But by selecting regional natives you will be preserving the natural character of your area. You will also be preserving the complex interrelationships between the native plants and the butterflies, birds, and myriad other creatures with which they have coevolved.– Brooklyn Botanic Garden