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While almost all invasive plants are non-native, not all non-native plants are
invasive. Non-native plants, which are sometimes referred to as exotics, are plants that are
growing outside of their native range due to the action of human beings. They are mostly
introduced through the horticulture industry. While the majority of these non-native plants
do not spread beyond where they were planted, some of them become invasive. There are many
definitions for invasive species. The Nature Conservancy defines an invasive plant as a
species which spreads from human settings (gardens, agricultural areas, etc.) into the wild.
Once in the wild, invasive species may continue to reproduce, and displace native species.
They often spread rapidly and can seriously alter natural habitats.
Invasives are one of the major threats facing wildlands. An assessment of
plants and animals on the endangered species list in 1998 found that 49% of them were negatively
impacted by invasives. Only direct habitat destruction impacts endangered species more severely.
Invasive plants can degrade natural communities in a number of ways.
They may displace native species. An example of this is Japanese privet, also known as
Ligustrum. Privet has invaded many areas of the Balcones Canyonlands Preserve and has
formed thickets in some riparian areas, displacing native riparian plants. It also has
phenolic compounds which make it resistant to insect herbivory, giving it an advantage
over some native shrubs. Other invasives like Tree of Heaven (Ailanthus altissima)
damage natural communities by inhibiting recruitment of select species and altering
successional patterns. The tree of heaven produces toxins which prevent other plants
from getting established and changes the soil conditions.
The most important thing a person can do to reduce the threat of invasive species is become
educated. There are numerous websites devoted to invasive species including texasinvasives.org. Many invasives can still be bought at local nurseries,
but an informed gardener can avoid buying and planting them. Property owners should consider
replacing invasive species in their landscape over time, especially if they border a creek or
natural area where birds or other vectors might eventually carry them beyond their borders.
Volunteering with organizations that remove invasive plants
from parks and preserves is another good way to learn more about them.
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