Every species of plant has a native range. This is a region or habitat where the plant occurs naturally, meaning it has adapted to the local climate, soils, and surrounding species of plants and animals over thousands of years without any direct or indirect human action. When a species occurs outside of this native range, it is called a non-native or exotic species. Non-native species can be brought in from other habitats, ecosystems, regions, or even continents. For instance, Johnson Grass was introduced into the United States from its native range around the Mediterranean Sea.
The population of a plant species in its native range is controlled by a number of complex factors, including disease, parasites, and herbivorous (plant-eating) species. However, in a new environment, free from these natural constraints, some exotic species can undergo rapid and unrestricted growth, spreading over large areas. When an exotic species exhibits this rapid growth and spread, it is called an invasive species. One of the most notorious invasive plants in the southern United States is a climbing vine known as kudzu, or “the plant that ate the South.” Originally introduced to reduce soil erosion, kudzu can grow up to a foot a day, smothering native trees and shrubs under a solid blanket of leaves.
As demonstrated by the kudzu example, invasive species can severely threaten the ecology of the natural ecosystem, often outcompeting native plants for space and resources and disrupting the food chain. For example, chinaberry—an invasive tree found on the Preserve—grows extremely fast and forms dense thickets that shade out and exclude the native vegetation many birds, mammals, and insects rely upon for food and habitat. The vines of Japanese honeysuckle can kill native shrubs and trees by twisting tightly around the stem or trunk and cutting off the flow of water through the plant. Particularly devastating, the tree-of-heaven prevents the establishment of other plant species by releasing a toxin through its roots that functions as an herbicide.
Removal and control of invasive species is a critical part of Preserve management. The major source of invasive species on the Preserve is from the gardens and landscaping of nearby homes. One of the best ways to prevent this threat is through native landscaping, which is discussed further in the In the Neighborhood section. Native landscaping benefits native wildlife and reduces the staff time and budget consumed by the removal and control of invasive plants.