Section 1: Introduction - Impacts of Invasive Plants on Prairies and Grasslands

Native tallgrass prairie historically covered 140 million acres of North America. These ecologically important grasslands included a mix of species such as big bluestem (Andropogon gerardii), Indiangrass (Sorghastrum nutans), and switchgrass (Panicum virgatum) along with native forbs (wildflowers) such as black-eyed susan (Rudbeckia hirta) and wild bergamot (Monarda fistulosa).

It is estimated that as much as 99 percent of native tallgrass prairie has been destroyed or severely impaired in the midwestern United States. This highlights the importance of protecting existing prairie from invasive plants, and reconstructing or restoring* mixed forb-grass prairie ecosystems.

A land manager’s ability to reconstruct or rehabilitate mixed forb-grass prairie landscapes is often compromised by the presence of invasive plants such as Canada thistle (Cirsium arvense L.) and sweet clover (Melilotus officinalis). Although best management practices recommend applying herbicides to control noxious and invasive weeds prior to establishing mixed grass prairie systems, there is concern about the effect of herbicide residues on forb establishment.

Fire suppression, removal of native nomadic grazers, and continued human disturbance, allow for the spread and establishment of invasive plants on prairies and grasslands. Invasion by herbaceous weeds and woody plants has become a major threat to the conservation of biodiversity and ecosystem sustainability in both remnant and restored prairies (Figure 1.1).
Invasive plants can:

  • Compete with and displace native plants and animals.
  • Alter structure, organization and function of native plant communities, and threaten biodiversity.
  • Hybridize with native species.
  • Impact soil and water resources and promote other invaders.
  • Alter fire regimes.

The good news is that many plant invasions can be reversed, halted or slowed, and many degraded sites can be restored to healthy systems dominated by native species. In some instances this requires taking action to control and manage invasive plants to meet conservation goals.

*Reconstruction means starting with bare soil (such as a former crop field). Rehabilitation means starting on land that already contains some remnant species. Restoration is defined as “the process of bringing back to an original condition,” and thus includes both rehabilitation and reconstruction.