Spring-applied treatments offer another window of opportunity for revegetation of annual grass-invaded rangelands

Authors: Davies, Kirk; SCHROEDER, VANESSA - Oregon State University; JOHNSON, DUSTIN - Oregon State University; Svejcar, Lauren; CLENET, DANIELLE - Oregon State University

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2024
Publication Date: 2/8/2024
Citation: Davies, K.W., Schroeder, V.M., Johnson, D.D., Svejcar, L.N., Clenet, D.R. 2024. Spring-applied treatments offer another window of opportunity for revegetation of annual grass-invaded rangelands. Rangeland Ecology and Management. 93:104-111. https://doi.org/10.1016/j.rama.2024.01.002.
DOI: https://doi.org/10.1016/j.rama.2024.01.002

Interpretive Summary: Restoration of perennial vegetation in annual grass-invaded rangelands is a management priority. Traditional revegetation involves fall control of annual grasses, but additional treatment windows are needed because the fall treatment window is relatively short. We evaluated spring applied control treatments followed with fall seeding of a perennial bunchgrass. Spring treatments that included a pre-emergent herbicide, imazapic, followed by fall seeding successfully controlled annual grasses and substantially increased bunchgrass abundance. Spring burning prior to imazapic application was the most successful revegetation treatment. These results suggest that spring applied control treatments can be part of a successful revegetation program. Land, weed, and other natural resource managers will find this information useful.

Technical Abstract: Invasive annual grasses have degraded tens of millions of hectares of the sagebrush ecosystem of west- ern North America. Restoration of perennial vegetation in annual grass-invaded rangelands is a man- agement priority to decrease fire risk, increase livestock forage quality, and improve wildlife habitat. Annual grasses are traditionally controlled in the fall with preemergent herbicides, such as imazapic, and treated areas are often seeded with perennial bunchgrasses 1 yr later to avoid nontarget herbicide damage to revegetation species. However, there is a limited window of time in the fall to accomplish an- nual grass control treatments. Spring-applied control treatments may be another option compared with only fall control treatments, but they have received little attention. We imposed spring-applied annual grass control treatments followed by fall seeding of a perennial bunchgrasses and then measured vege- tation response for the next 3 yr in cheatgrass (Bromus tectorum) and medusahead (Taeniatherum caput- medusae)-invaded communities. Spring treatments that included imazapic application (at a low rate), followed by fall seeding of perennial bunchgrasses, successfully controlled annual grasses and substan- tially increased perennial bunchgrass cover and density. Spring burning and glyphosate herbicide appli- cation, without imazapic, were not successful in promoting substantial increases in perennial bunchgrass cover. Spring burning before imazapic application was the most successful treatment for rehabilitation seeding. By the third yr after seeding, perennial bunchgrass cover was 17% in the spring burn-imazapic treatment, greater than what is generally found in intact Wyoming big sagebrush ( Artemisia tridentata ssp. wyomingensis )-bunchgrass communities in this region. The results of this study provide strong ev- idence that spring-applied control treatments including imazapic can be part of successful revegeta- tion efforts, thereby decreasing some of the logistical challenges associated with revegetation of annual grass-invaded sagebrush rangelands.