Indicators of ventenata invasion in sagebrush steppe rangelands
Though widely distributed throughout the study region, ventenata only 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 high V. dubia cover. Nonmetric multidimensional scaling analysis revealed that ventenata and medusahead were closely associated. Furthermore, chi-square indicator analysis showed that T. caput-medusae was more prevalent, while mountain big sagebrush was less prevalent, in plots containing ventenata. Abiotic factors that explained variation in ventenata abundance included rock cover, soil depth, and a north/south aspect. Higher ventenata cover 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 of ventenata in sagebrush steppe communities should focus on moist areas and sites susceptible to invasion by medusahead.