Success of Seeding Native Compared with Introduced Perennial Vegetation for Revegetating Medusahead-Invaded Sagebrush Rangeland

Abstract

Millions of hectares of Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young) rangeland have been invaded by medusahead (Taeniatherum caput-medusae [L] Nevski), an exotic annual grass that degrades wildlife habitat, reduces forage production, and decreases biodiversity. Revegetation of medusahead-invaded sagebrush plant communities is necessary to restore ecosystem services. Disagreement, however, exists over whether to seed native or introduced perennial species to revegetate communities after controlling medusahead. Though native species generally do not establish as well as introduced species, interference from co-seeded introduced species has often been attributed to the limited success of natives. The potential for seeding natives to revegetate communities after medusahead control is relatively unknown because they have been largely co-seeded with introduced species. We compared the results of seeding native and introduced perennial species after controlling medusahead with prescribed burning followed with an imazapic herbicide application at five sites. Perennial bunchgrass cover and density were 5- and 10- fold greater in areas seeded with introduced compared with native species 3 years post seeding. Furthermore, exotic annual grass cover and density were less in areas seeded with introduced compared with native species. Seeded introduced and native shrubs largely failed to establish. High perennial bunchgrass density (15 individuals m⁻²) in areas seeded with introduced species in the third year post seeding suggests that the succession trajectory of these communities has shifted to becoming perennial dominated. Average perennial bunchgrass density of 1.5 individuals m⁻² with seeding native species will likely not limit medusahead and appears to already be converting back to exotic annual grass-dominated communities. These results suggest that seeding introduced compared with native species after medusahead control will likely be more successful. Our results also imply that if natives are selected to seed after medusahead control, additional resources may be necessary to recontrol medusahead and repeatedly sow native species.Keywords: Restoration, Forage kochia, Bunchgrasses, Crested wheatgrass, Exotic annual grasses, Imazapic, Wyoming big sagebrus