Abiotic constraints on the competitive ability of exotic and native grasses in a Pacific Northwest prairie

Abstract

In prairie ecosystems, abiotic constraints on competition can structure plant communities; however, the extent to which competition between native and exotic plant species is constrained by environmental factors is still debated. The objective of our study was to use paired field and greenhouse experiments to evaluate the competitive dynamics between two native (Danthonia californica and Deschampsia cespitosa) and two exotic (Schedonorus arundinaceus and Lolium multiflorum) grass species under varying nutrient and moisture conditions in an upland prairie in the Willamette Valley, Oregon. We hypothesized the two invasive, exotic grasses would be more competitive under high-nutrient, moderate-moisture conditions, resulting in the displacement of native grasses from these environments. In the field, the experimental reduction of competition resulted in shorter, wider plants, but only the annual grass, Lolium multiflorum, produced more aboveground biomass when competition was reduced. In the greenhouse, the two exotic grasses produced more total biomass than the two native grasses. Competitive hierarchies were influenced by nutrient and/or moisture treatments for the two exotic grasses, but not for the two native grasses. L. multiflorum dominated competitive interactions with all other grasses across treatments. In general, S. arundinaceus dominated when in competition with native grasses, and D. cespitosa produced the most biomass in monoculture or under interspecific competition with the other native grass, D. californica. D. californica, D. cespitosa, and S. arundinaceus all produced more biomass in high-moisture, high-nutrient environments, and D. cespitosa, L. multiflorum, and S. arundinaceus allocated more biomass belowground in the low nutrient treatment. Taken together, these experiments suggest the competitive superiority of the exotic grasses, especially L. multiflorum, but, contrary to our hypothesis, the native grasses were not preferentially excluded from nutrient-rich, moderately wet environments.

The roles of biotic resistance and nitrogen deposition in regulating non-native understory plant diversity

“…Non-native plant species have been found to grow more rapidly than native plants and therefore have a high demand for soil N (Ehrenfeld 2003)leading to increased N uptake in high N environments Pfeifer-Meister et al 2008). Non-native species also have been shown to have high resourceuse efficiency, which could explain why they tolerate competition with native species in N-poor environments (Funk and Vitousek 2007;Johnson et al 2003;Pfeifer-Meister et al 2008).…”

Context-dependent pattern and process: the distribution and competitive dynamics of an invasive grass, Brachypodium sylvaticum

“…Results from the field experiment show that when competition is removed, B. sylvaticum size increases, and it spreads out to fill available space. A recent study of several other grasses (Pfeifer-Meister et al 2008) documented a similar response to reductions in surrounding competition. Our greenhouse results indicate that competition with other species regulates the biomass of B. sylvaticum in the sun whereas competition with itself is more important in the shade.…”

“…where Y ij is the mean of B. sylvaticum grown with another species and Y i is the mean biomass of B. sylvaticum in monoculture for that treatment (Harper 1977;Wetzel and van der Valk 1998;Pfeifer-Meister et al 2008). In this analysis, a value of one is always obtained for the monoculture.…”

“…In this analysis, a value of one is always obtained for the monoculture. To determine whether growth in the mixtures within each treatment was significantly different from one, we used one-sample t tests (Pfeifer-Meister et al 2008).…”

Responses to simulated nitrogen deposition in invasive and native or non-invasive clonal plants in China

“…One of the most consistent findings of tests of this hypothesis has been that an increase in the availability of N can promote the spread of introduced species of plants in terrestrial habitats (Pfeifer-Meister et al 2008;Rao and Allen 2010;Dukes et al 2011;Li et al 2011;Mozdzer and Zieman 2010;Mozdzer and Megonigal 2012). This is of particular ecological interest because anthropogenic increases in N availability through aerial deposition and agricultural application of fertilizers are a major component of global change (Bobbink et al 2010;Henrys et al 2011;McClean et al 2011). Together, this previous work suggests that it would be useful and timely to test whether greater ability to increase performance in response to increase in N availability is associated with greater invasiveness in clonal plant species.…”