The relevance of diversity-biotic resistance studies to conservation of biodiversity could be improved by simultaneously examining the drivers of regional diversity and their effects on local species diversity and invasion. Using path analysis, I examined direct and indirect effects of various abiotic factors (i.e., flooding, treefall gaps, soil texture, proximity to roads, and stand age) on plant species richness, floristic quality (a proxy for regional plant diversity), and the abundance of a non-native invasive grass, Microstegium vimineum, in 117 3.14-m2 plots within four stands of mesic floodplain forests in northern Mississippi. Results of this study showed a significant negative effect of species richness on M. vimineum abundance in year two. However, species richness varied in response to flooding and gaps, and the positive indirect effects of flooding and gaps on M. vimineum abundance mediated through reductions in species richness in fall 2008 were not nearly as great as the positive direct effects of these disturbances on M. vimineum abundance. In contrast to species richness, floristic quality (weighted mean fidelity to mesic forests or wetlands minus fidelity to anthropogenically disturbed areas) responded positively to gaps in flooded areas and was not affected by M. vimineum. Altogether, these results suggest that the same factors that reduce biotic resistance have even greater direct positive effects on the abundance of an invasive grass and native floodplain specialists. Control of M. vimineum in mature floodplain forest ecosystems should be done selectively to avoid collateral damage of native floodplain specialists.