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Submodule 3: Invasive Plants
Consequences of Terrestrial Plant Invasions
Invasive terrestrial plants are those plants that invade new territories and establish stands outside of their native locations. In addition to many of the traits described above, these plants can thrive because there are few if any natural diseases or herbivores to inhibit growth. Because of this often explosive growth, invasive plants overrun their new environment and degrade the native habitat. Native plants provide basic needs (food and shelter) for organisms including birds and mammals; therefore of native flora can change an entire ecosystem. These plants may not show invasive tendencies in their native environment, but, given the opportunity in a new environment, they encroach on their neighboring plants taking an unfair share of space and resources.
Woody plants, grasses, and herbaceous annuals and perennials make up the bulk of invasive plants. Each presents its own particular set of problems when invading a new ecosystem such as:
Woody plants: mainly introduced for landscape purposes; some imported for erosion control. Usually require a longer period for establishment compared to herbaceous invasives.
Grasses: non-native grasses have a significant effect on fire frequency, primarily on US rangelands. This pattern does not allow for the establishment of rangeland shrubs.
Herbaceous annuals and perennials: many introduced from contaminated crop seeds. Also, soil used as ballast in cargo ships was often dumped in this country to make room for freight.
Terrestrial plant invasions characteristically occur in three stages:
- Introduction the invasive plant arrives at a new habitat (see Pathways).
- Colonization the plant becomes established; depends on its successful reproduction.
- Naturalization become acclimated to the new habitat through the establishment of large stands and the reallocation of resources to itself.
It is important to highlight again that it is less expensive and more reliable to prevent infestations from occurring in the first place than it is to try and control them or eradicate them once an infestation has occurred. Once an infestation is established, it can be very difficult to eliminate things such as seeds, which can remain dormant for years, or rhizomes, which can sprout new plants when environmental conditions permit.
Mojave Grass (photo courtesy USGS)
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