Chapter 7: Human Alterations to Riparian Areas
Invasive
Exotic Species
- Of the 22,000 plant species in the United States approximately 23% are considered exotic.
- Along the Rio Grande in New Mexico, it is estimated that 25% of the herbaceous plants and 40% of tree species are exotic.
- Riparian areas have some the most aggressive invasive exotics.
- Some of Arizona’s exotic plants: saltcedar, Russian olive tree, tree of heaven, silktree, purple loosestrife, Bermudagrass, Johnsongrass, buffelgrass, Russian knapweed, Lehmann lovegrass, Eurasian watermilfoil, water hyacinth, and cheatgrass.
Figure 7.24. Plant invasive species of Arizona: Saltcedar (top left), tree of heaven (top right), and bermudagrass (bottom).
- Some of Arizona’s exotic animals: American bullfrogs, virile crayfish, small-mouthed bass, bluegill, sunfish, and channel catfish.
Figure 7.25. Animal invasive species of Arizona: crayfish (left), and American bullfrog (right).
- Invasive exotic species outcompete their native peers because of the lack of natural controls on their populations, including predation, parasites, or pathogens.
- Human changes (i.e., reduction of flooding events) can give a competitive edge to invasive exotic species.
- Invasive exotic species are a major cause of decline for threatened or endangered species.
- Things to do to reduce invasive (noxious) weeds in Arizona.
- Learn to identify invasive (noxious) weeds that occur in your area.
- Use weed free forage for livestock.
- Clean all vehicles/equipment and inspect clothing and pets before leaving an infested area.
- Eliminate individual weeds before they become patches - Early detection/Rapid response.
- Pull small populations before they've flowered.
- Minimize disturbance and maintain native plant communities.
