Post-fire management decisions have consequences: Drill-seeding disturbance and effects of co-seeding introduced with native bunchgrasses

Abstract

Wildfires and the demand for post-fire seeding are increasing in the sagebrush ecosystem threatened by invasive annual grasses. Drill-seeding bunchgrasses after wildfire is a common strategy for limiting annual grasses. However, there are concerns that the soil disturbance associated with drill-seeding may negatively impact the plant community, particularly if seeded species fail to establish. Similarly, there are worries that co-seeding introduced bunchgrasses with natives, to hedge against low native bunchgrass establishment, may limit native bunchgrass success. We investigated the effects of the disturbance of drill-seeding and the impacts of co-seeding introduced bunchgrasses after wildfire in sagebrush communities at four sites up to six years post-seeding. The disturbance of drill-seeding increased invasive annual grasses from ∼10 % to >15 % cover and increased its density by >200 plants∙m−2 by the end of the study. Bunchgrasses appeared to not be influenced by the disturbance of drill-seeding; however, drill-seeding slightly reduced perennial forb density. These results suggest that restoration practitioners need to consider potential negative consequences of drill-seeding, especially when and where selected plant materials may fail to establish in high abundance. Co-seeding introduced bunchgrasses with native bunchgrasses limited native bunchgrasses and also slightly decreased native perennial forbs. However, co-seeding introduced bunchgrasses reduced invasive annual grasses by ∼50 %, while seeding only native bunchgrasses did not reduce annual grasses. These findings suggest that co-seeding introduced and native bunchgrasses may not be advisable. We suggest: 1) If native bunchgrasses are unlikely to establish in high abundance, then introduced bunchgrasses should be used, and 2) If seeded native bunchgrasses are likely to meet management objectives, then introduced bunchgrasses should not be co-seeded. Additional investigations are needed in other areas to determine the applicability of the results of this study to the larger sagebrush ecosystem. Clearly, the potential consequences of post-fire management will need to be considered as restoration plans are developed, but additional research is needed to better inform management decisions.