Native vegetation composition in crested wheatgrass in northwestern Great Basin

Authors: NAFUS, ALETA - Oregon State University; SVEJCAR, TONY - Retired ARS Employee; Davies, Kirk

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2019
Publication Date: 1/1/2020
Citation: Nafus, A.M., Svejcar, T.J., Davies, K.W. 2020. Native vegetation composition in crested wheatgrass in northwestern Great Basin. Rangeland Ecology and Management. 73(1):9-18. https://doi.org/10.1016/j.rama.2019.10.006.
DOI: https://doi.org/10.1016/j.rama.2019.10.006

Interpretive Summary: Crested wheatgrass is an introduced bunchgrass that has been seeded on millions of hectares in the western US to prevent weed invasion and provide forage for livestock. Seeding crested wheatgrass is expected to result in the exclusion of native vegetation and the development of crested wheatgrass monocultures, but information is lacking regarding native vegetation variability in crested wheatgrass stands. We investigated the variability of native vegetation in crested wheatgrass stands and correlations with environmental factors. Plant community composition of crested wheatgrass stands was variable and environmental factors explained up to 56% of this variation. This research suggests that seeding crested wheatgrass does not always result in monocultures, as many seedings contained a diverse assemblage of native vegetation.

Technical Abstract: Crested wheatgrass, an introduced perennial bunchgrass, has been seeded extensively on the rangelands of western North America. There is a perception that this species is very competitive and that it forms monoculture or low diversity stands where successfully seeded. However, there is limited information on species composition in sites previously seeded to crested wheatgrass. We measured native vegetation and environmental characteristics in areas seeded with crested wheatgrass across the northwestern Great Basin. Plant community composition within these crested wheatgrass stands was variable, from seedings that were near monocultures of crested wheatgrass to those that contained more diverse assemblages of native vegetation, especially shrubs. Environmental factors explained a range of functional group variability from 0% of annual grass density to 56% of large native bunchgrass density. Soil texture appeared to be an important environmental characteristic in explaining vegetation cover and density. Native vegetation was, for all functional groups, positively correlated with soils lower in sand content. Our results suggest environmental differences explain some of the variability of native vegetation in crested wheatgrass stands, and this information will be useful in assessing the potential for native vegetation to co-occupy sites seeded with crested wheatgrass. This research also suggests that crested wheatgrass seedings do not always remain in near monoculture vegetation states as seedings substantially varied in native vegetation composition and abundance with some seeded areas having a more diverse assemblage of native vegetation. In half the sites, there were five or more perennial herbaceous species and 63% of sites contained Wyoming big sagebrush. Although not exclusively true, species most commonly encountered in crested wheatgrass seedings are those that are able to minimize competition with crested wheatgrass via temporal (i.e., Sandberg bluegrass, annual forbs, annual grasses) or spatial (i.e., shrubs) differentiation in resource use.