Indicators of Ventenata (Ventenata dubia) Invasion in Sagebrush Steppe Rangelands

Abstract

AbstractVentenata [Ventenata dubia(Leers) Coss.], an invasive winter annual grass, significantly reduces forage production in grassland systems and displaces species within both perennial- and annual-dominated grasslands within the Inland Northwest. The range ofV. dubiais expanding into sagebrush steppe communities, an expansive habitat critical for forage production, wildlife, and recreation. Currently, there is limited knowledge ofV. dubia’s distribution and abundance within sagebrush steppe communities. We performed field surveys at 15 locations in sagebrush steppe rangelands in southern Idaho and eastern Oregon to assess whereV. dubiaoccurs, with the aim of providing insight about its niche in this new habitat. Specifically, we evaluated biotic and abiotic factors of the plant community as indicators ofV. dubiapresence. We also correlated species diversity measures with no, low (<12.5%), and high (>12.5%)V. dubiacover. Though widely distributed throughout the study region,V. dubiaonly appeared in 45% of the 225 plots, and foliar cover was typically less than 50%. It was primarily found in ephemerally wet microhabitats. Species richness and the Shannon diversity index were lowest in plots with highV. dubiacover. Nonmetric multidimensional scaling analysis revealed thatV. dubiaand medusahead [Taeniatherum caput-medusae(L.) Nevski] were closely associated. Furthermore, chi-square indicator analysis showed thatT. caput-medusaewas more prevalent, while mountain big sagebrush [Artemisia tridentataNutt. spp.vaseyana(Rydb.) Beetle] was less prevalent, in plots containingV. dubia. Abiotic factors that explained variation inV. dubiaabundance included rock cover, soil depth, and a north/south aspect. HigherV. dubiacover also correlated with higher clay content and lower phosphorus and potassium concentrations in the soil. We suggest that at this point, detection survey efforts to locate incipient infestations ofV. dubiain sagebrush steppe communities should focus on moist areas and sites susceptible to invasion byT. caput-medusae.