Restoration of exotic annual grass-invaded rangelands: importance of seed mix composition

Authors: Davies, Kirk; JOHNSON, DUSTIN - Oregon State University; NAFUS, ALETA - Oregon State University

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2013
Publication Date: 6/30/2014
Publication URL: http://handle.nal.usda.gov/10113/59313
Citation: Davies, K.W., Johnson, D.D., Nafus, A.M. 2014. Restoration of exotic annual grass-invaded rangelands: importance of seed mix composition. Invasive Plant Science and Management. 7(2):247-256. DOI: 10.1614/IPSM-D-12-00093.1.

Interpretive Summary: Ecological theory suggests that increasing species and plant functional group diversity in seed mixes used to revegetate exotic annual grass-invaded sagebrush rangelands should improve success. However, this idea has not been tested and the cost of seeding increases substantial with the inclusion of less available plant functional groups compared to seeding only the dominant plant functional group, perennial bunchgrasses. We investigated the influence of seed mix diversity on desirable plant and exotic annual grass cover and density. We did not find evidence that greater seed mix diversity increased desirable vegetation or decreased exotic annual grass dominance more than seeding only perennial bunchgrasses. Our results suggest that it is critical to include perennial bunchgrasses in seed mixes used to restore exotic annual grass-invaded rangelands.

Technical Abstract: Restoration of exotic annual grass-invaded rangelands is needed to improve ecosystem function and services. Increasing plant species and plant functional group diversity is generally believed to increase resistance to invasion and increase desired vegetation. However, the effects of diversity and individual plant functional groups in seed mixes used to restore exotic annual grass-invaded rangelands have not been investigated. We evaluated increasing the diversity of species and functional groups seeded after exotic annual grass control to restore desirable vegetation (perennial herbaceous vegetation) and limit exotic annual grasses at two sites in southeastern Oregon. We also investigated the effects of seeding individual plant functional groups on plant community characteristics. Large perennial grasses, the dominant herbaceous plant functional group, were the most important functional group to seed for increasing perennial herbaceous vegetation cover and density. We did not find evidence that greater seed mix diversity increased perennial herbaceous vegetation or decreased exotic annual grass dominance more than seeding only the dominant species or dominant plant functional group. None of the seed mixes had a significant effect on exotic annual grass cover or density, but the lack of a measured effect was probably due to low annual grass propagule pressure in the first couple of years after annual grass control and an unusually wet-cool spring in the third year post-seeding. Though our results suggest that seeding only the dominant plant functional group will likely maximize plant community productivity and resistance to invasion, seeding a diverse seed mix may have benefits to higher tropic levels and community stability. Clearly the dominant species are the most prudent to include in seed mixes to restore exotic annual grass-invaded plant communities, especially with finite resources and an increasingly large area in need of restoration.