Testing Techniques for Restoring Native Prairies Leads to Better Decision-Making

Restoring prairies to their native vegetation can be approached from several directions. Managers might eliminate invasive plants through use of herbicides, encourage growth of native species through seeding, or manipulate conditions to favor native species. Research that provides evidence for making these decisions can be invaluable for resource management.

The current issue of the journal Invasive Plant Science and Management provides an evaluation of restoration methods. Researchers sought to develop a decision mechanism that considers the composition of plants currently growing and applies restoration techniques tailored to an area’s specific challenges.

Two prairie remnants in the Pacific Northwest served as study sites. These locations, originally part of the Palouse Prairie, grow native plants such as Idaho fescue, bluebunch wheatgrass, arrowleaf balsamroot and common yarrow. They have been threatened primarily by downy brome and ventenata, two invasive annual grasses. This study tested methods of removing invasive annual grasses with herbicide applications and supplementing native perennial species through seeding.

Researchers first assessed the plant communities present on these pieces of prairie. They identified areas as predominantly annual, if less than 10 percent of native perennial plants were present; mixed, if an area had 15 percent to 25 percent of native perennial grasses; and predominately perennial, if more than 25 percent of the grasses were native perennials.

Within each of these three types of plant communities, five treatments and a control were established. These five treatments were broadcast herbicide application, spot herbicide application, broadcast herbicide with seeding and mulching, spot herbicide with seeding and mulching, and seeding and mulching only.

The response to these treatments varied. Overall, the findings show that predominately perennial plant communities do not benefit from added seed, but spot herbicide application does reduce the cover of annual grass. Mixed plant communities require broadcast herbicide application to help native species survive. And predominately annual plant communities should be seeded along with the use of broadcast herbicide.