| Microstegium vimineum (Trin.) A. Camus (Japanese grass) is a non-native plant of particular ecological concern in the United States due to its potential impact on native ecosystems, yet little is known of its ecological requirements. In spite of its rapid expansion throughout its introduced range, it is not found in many apparently suitable locations, which suggests that certain environmental factors, or interactions of factors, limit the distribution of this invasive grass. I used a combination of field and greenhouse experiments and a biogeographical survey to examine environmental factors that might cause the complex pattern of presence/absence and performance exhibited by this species.; Within the study area, M. vimineum exhibited the broad environmental tolerance of many "weedy" species. Soil pH was the only environmental variable, among those measured, that was correlated with the presence of M. vimineum, whereas canopy openness and other species biomass are the most important variables that explain the performance (i.e., height and biomass) of M. vimineum.; It has been suggested that light and water are mutually substitutable resources for plants. I conducted a greenhouse experiment to test a hypothesized light/water trade-off in M. vimineum, whereby light and water would be mutually substitutable and would have an interactive effect on plant growth. Results demonstrate a light/water trade-off in M. vimineum in terms of root, shoot, and total biomass accumulation. Shifts in biomass accumulation between roots and shoots does not appear to be the mechanism responsible for the trade-off, but stomatal conductance remains a plausible mechanism that should be tested in future research.; M. vimineum often occurs as extensive, dense patches with sharp boundaries and distinct gaps in cover. One example of this distributional pattern was observed relative to the native shrub Asimina triloba (pawpaw), whereby M. vimineum cover ended abruptly at the drip line of the patch. I conducted field and greenhouse experiments to test several hypotheses regarding the causes of this pattern of M. vimineum distribution, including allelopathy, lack of seed dispersal, soil moisture limitations, and light limitations. I concluded that light reduction by the A. triloba canopy prevented establishment of M. vimineum beneath this shrub. |
