Biological invasions can substantially alter the availability of limiting resources and consequently reduce the diversity and productivity of native plants in invaded communities. In eastern deciduous forests, invasions of Microstegium vimineum (Japanese stiltgrass) are of particular concern because this aggressive exotic grass forms dense patches with a persistent litter layer that potentially influences the availabilities of aboveground and belowground resources in understory communities. The impact of M. vimineum can be ecologically devastating in invaded communities, but the mechanisms underlying such effects have not been clarified. Here we present results from a long-term experimental field study that assesses how M. vimineum alters resource availabilities and impacts understory plant communities. We measured light, soil moisture, and soil nitrogen availabilities as well as understory plant productivity and diversity at regular intervals for 2 yrs following an experimental introduction of M. vimineum. We compared such measures between invaded and uninvaded plots.

Results/Conclusions

We demonstrate that M. vimineum substantially reduced the availability of light within the understory but had negligible effects on the availabilities of soil moisture and nitrogen. The presence of M. vimineum also reduced the productivity and diversity of the understory community, and these reductions were more pronounced in the second year following invasion. Our results indicate that light reduction within invaded communities is a likely mechanism by which M. vimineum suppresses native vegetation.