Postfire Seeding of Native Compared With Introduced Bunchgrasses Followed 3 Yr Later With Invasive Annual Grass Control

Abstract

Invasive annual grasses threaten the ecological integrity of the sagebrush ecosystem, often increasing when wildfires or other disturbances reduce perennial vegetation. In response to this threat, perennial bunchgrasses are often seeded after wildfire. Because of greater success in establishment, introduced bunchgrasses are often selected for seeding instead of commercially available native bunchgrasses. However, locally sourced native bunchgrasses appear to establish better than generally expected for commercially available native bunchgrasses but introduced bunchgrasses still establish better and result in greater suppression of invasive annual grasses. In areas where native bunchgrasses have been established from seeding but annual grass abundance remains high, selective control of annual grasses may improve success. Comparisons between areas where locally sourced native and introduced bunchgrasses were seeded and established, followed by annual grass control, are lacking. We investigated vegetation characteristics in areas drill-seeded with introduced compared with locally sourced native bunchgrasses after a wildfire that received selective annual grass control (imazapic application) 3 yr after seeding. Treatments that were seeded with locally sourced native or introduced bunchgrasses followed by spraying imazapic increased bunchgrass cover and density compared with areas not seeded but sprayed with imazapic. Bunchgrass cover and density were greater in areas seeded with introduced compared with native bunchgrasses and sprayed with imazapic. Invasive annual grass abundance was reduced with seeding introduced bunchgrasses followed with imazapic application, but not with seeding locally sourced native bunchgrasses followed with spraying imazapic. These results suggest that locally sourced native bunchgrasses have the potential for restoration success, but research needs to determine what follow-up treatments (e.g., additional seeding, longer-term annual grass control, and more diverse seed mixes) are needed to further promote perennial vegetation abundance and increase resistance to annual grasses to achieve similar outcomes as seeding introduced bunchgrasses.