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Role of competition in restoring resource poor arid systems dominated by invasive grasses

Mangla, S., Sheley, R.L., James, J.J., Radosevich, S.R.
Journal of arid environments 2011 v.75 no.5 pp. 487
Poa secunda, Pseudoroegneria spicata, biomass, ecosystems, field experimentation, invasive species, linear models, managers, plant establishment, regression analysis, survival rate, vegetation
Understanding the role competition intensity and importance play in directing vegetation dynamics is central to developing restoration strategies, especially in resource poor environments. We hypothesized 1) competition would be intense among invasive and native species, but 2) competition would be unimportant in explaining variation in target plant biomass and survivorship relative to other factors driving these variables. We performed a two year addition series field experiment to quantify competition intensity and importance. Densities of two invasive (cheatgrass and medusahead) and two native (Sandberg’s bluegrass and bluebunch wheatgrass) species were arranged in monocultures and mixtures of two, three and four species, producing varying total densities and species proportions. Multiple linear regression models predicting individual plant biomass and survivorship were developed. Based on biomass, competition intensity coefficients ranged from −0.38 to 0.63 with R² < 0.06. All survivorship data produced poor fitting regression models (R² < 0.05). Our results suggest neither competition intensity nor importance influenced plant dominance in resource poor environments during the two years of establishment. Land managers may be more successful at restoration of resource poor ecosystems by overcoming abiotic barriers to plant establishment rather than focusing on plant–plant interactions.