Long-term evaluation of restoring understories in Wyoming big sagebrush communities with mowing and seeding native bunchgrasses

Abstract

Restoring degraded plant communities is a global challenge and a major priority for land managers and conservationists. Degraded Wyoming big sagebrush communities (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) have high sagebrush cover with a depleted perennial herbaceous understory. They are widespread in western North America and are a priority for restoration because they provide habitat for sagebrush-associated species and an important forage base for livestock production. Mechanically reducing sagebrush with mowing has been attempted to restore the understory in these communities but often fails because large native perennial bunchgrasses do not increase and exotic annual grasses proliferate. Seeding large native perennial bunchgrasses after mowing sagebrush may increase their density or cover and thereby limit exotic annual grasses. Native perennial bunchgrasses are slow growing; thus, long-term studies are needed to evaluate this treatment strategy. We evaluated mowing followed by drill-seeding large native perennial bunchgrasses in southeastern Oregon for 11 yr post treatment. Large bunchgrass cover and density were approximately 2 × greater with mowing followed by seeding compared with the untreated control. However, mowing, with and without seeding, increased exotic annual grasses and decreased biological soil crusts. Sagebrush cover was less in mowed treatments compared with the untreated control, but sagebrush cover increased over time. Mowing and seeding native bunchgrasses was less successful than desired, particularly since exotic annual grasses increased substantially. This treatment may be improved by reducing the disturbance associated with mowing and drill seeding, decreasing exotic annual grass competition, and increasing the establishment of native perennial bunchgrasses. The results of our study indicate that seeding native bunchgrasses into degraded Wyoming big sagebrush communities has potential as a restoration treatment but needs refinement to improve success.