Is crested wheatgrass invasive in sagebrush steppe with intact understories in the Great Basin?

Authors: Davies, Kirk; Bates, Jonathan - Jon; Boyd, Chad

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2023
Publication Date: 4/15/2023
Citation: Davies, K.W., Bates, J.D., Boyd, C.S. 2023. Is crested wheatgrass invasive in sagebrush steppe with intact understories in the Great Basin? Rangeland Ecology and Management. 90:322-328. https://doi.org/10.1016/j.rama.2023.03.004.
DOI: https://doi.org/10.1016/j.rama.2023.03.004

Interpretive Summary: Crested wheatgrass is a non-native perennial grass often seeded after disturbances in sagebrush steppe communities. There are concerns that it may be invasive in intact sagebrush communities. We evaluated if crested wheatgrass was invasive in intact sagebrush communities by drill seeding it into five intact communities. After seven years, we found no evidence that crested wheatgrass was invasive in intact sagebrush communities, suggesting that these communities are competitive with crested wheatgrass and, thereby, limit its recruitment and growth. These results are of interest to other scientists and land managers.

Technical Abstract: Seeding crested wheatgrass (Agropyron desertorum [Fisch.] Schult.) in the sagebrush steppe is a controversial management action. There are concerns that crested wheatgrass may invade new areas and exclude native vegetation because many former crested wheatgrass seedings are near monocultures. However, crested wheatgrass is often seeded to prevent exotic annual grass invasion and stabilize soils after disturbances in areas where native vegetation is unlikely to establish. These areas can be difficult to identify and, consequentially, crested wheatgrass may be seeded in areas it is not needed, such as sagebrush steppe with understories dominated by native perennial grasses and forbs (intact understories). Thus, land managers need to know the potential effects of seeding crested wheatgrass, especially if it can invade and exclude native vegetation in sagebrush steppe with intact understories. We investigated the ability of crested wheatgrass to invade and exclude native vegetation by drill seeding crested wheatgrass into intact sagebrush steppe understories at five sites. To be invasive, crested wheatgrass would need to increase in abundance beyond initial establishment from drill seeding, causing decreases in native vegetation. We measured vegetation cover and density for 7 yr after seeding to evaluate the effects of seeding crested wheatgrass. Crested wheatgrass established with drill seeding but did not increase from its original density. Cover of crested wheatgrass increased with time but was < 2% seven yr after seeding. We found no evidence that seeding crested wheatgrass decreased the cover or abundance of native vegetation. These results suggest that intact sagebrush steppe understories are competitive with crested wheatgrass and, thereby, limit its recruitment and growth. Though crested wheatgrass did not show indications of being invasive in intact sagebrush steppe understories, longer-term evaluations with the inclusion of disturbances that might open safe sites in these communities would be prudent to fully understand its potential effects.