Role of Competition in Restoring Resource Poor Arid Systems Dominated by Invasive Grasses

An understanding of competition intensity and importance may be a useful step in helping managers understands how to prioritize restoration efforts in resource poor environments within the semi-arid steppe. The aims of this study were to quantify the intensity of competition among invasive annual grasses and native perennial bunchgrasses, and determine the importance of competition in explaining variation in target plant biomass and survivorship in a Wyoming big sagebrush steppe community type in southeastern Oregon, USA. Addition series experiments were conducted in 2008 and 2009 among four species. Treatments consisted of monoculture densities of each species to assess intraspecific competition, and mixtures of two, three and four species (interspecific competition), producing varying total densities and species proportions. We found no evidence that intensity of intra- or inter-specific competition were significant for the first two years species were establishing, regardless of the density used as the independent variable. Our results indicate that neither the intensity of competition nor the importance of competition explained variation in target plant biomass and survivorship for the first two years plants were establishing. Instead abiotic factors may have an overriding influence on plant biomass and survivorship.We propose four scenarios which may apply to semi-arid environments during the initial phase of restoration