Our thanks to Buckman for its support of the Wolf River Conservancy Education Program and the development of our online education resources.
Once an Exotic, Always an Exotic!
An estimated 3,500 species of exotic plants have escaped cultivation in the U.S., are able to reproduce in the wild, and have become established, or “naturalized”. These plants, however much a part of our current landscapes and ecosystems, are nonetheless exotic, since they were moved here by people. For centuries, horticulturists have imported and disseminated interesting new exotic plants. Unfortunately, many of these have become invasive pests that are having serious impacts to native species and ecosystems.
What Makes an Exotic Species Invasive? (When is a Guest a Pest?)
Many non-native species exist in apparent harmony in environments where they were introduced. For example, a relatively small number of exotic plants (e.g., corn,
wheat, rice, oats) form the basis of our agricultural industry and pose little to no known threat to our natural ecosystems. The most important aspect of analien plant is how it responds to a new environment. An invasive species is one that spreads and establishes over large areas, and persists. Invasiveness may be characterized and enhanced by robust vegetative growth, high reproductive rate, abundant seed production, high seed germination rate, and longevity. Some native plants exhibit invasive tendencies in certain situations.
How Many Plants are Invasive?
According to the Plant
Conservation Alliance’s Alien Plant Working Group, about 1,050 plant
species have been reported as being invasive in natural areas in the
United States. This represents an astonishing one-third or so of the
exotic plant species established and self-reproducing in the wild. Some
invasive species were planted intentionally for erosion control,
livestock grazing, wildlife habitat enhancement,and ornamental
purposes. Others have escaped from arboretums, botanical gardens, and
our own backyards.Free from the complex array of natural controls
present in their native lands, including herbivores,parasites, and
diseases, exotic plants may experience rapid and unrestricted growth in
How Bad Are Invasive Species?
Invasive species impact native plants, animals, and natural ecosystems by:
Reducing native biological diversity
- Altering hydrologic conditions & flooding regimes
- Altering soil characteristics
- Altering fire intensity and frequency
- Interfering with natural succession
- Competing for native pollinators
- Repelling or poisoning native insects
- Displacing rare plant species
- Increasing predation on native birds
- Serving as reservoirs of plant pathogens
- Replacing complex communities with monocultures
- Diluting the genetic composition of native species through hybridization