The role of environmental factors in the growth and suppression of <i>Microstegium vimineum</i> (Japanese stiltgrass)
Many invasive plants, including Microstegium vimineum (Japanese stiltgrass), are habitat generalists which tolerate a wide range of environmental conditions. This work focused on how environmental conditions affect population growth, abundance, and seed bank persistence of M. vimineum, as well as its response to suppression measures.
Patches of M. vimineum were planted into five environments and monitored for four years. Population growth tended to be highest in the roadside environment and lowest in intact forest, although due to the variability of the data, these differences were not significant. Small-scale environmental variables, particularly soil moisture and pH, explained much of the variation in final patch size.
To further investigate pH effects, field surveys compared M. vimineum along limestone and shale gravel roads. Soil pH along limestone roads was significantly higher than along shale roads as far as 25 m from the road edge. M. vimineum occupied significantly more of the roadside area along limestone than along shale roads.
To evaluate the influence of the environment on management outcomes, herbicide and mechanical treatments were applied to M. vimineum populations along forest roads, disturbed forest, and wetlands, and plant communities were monitored for three years. Selective herbicide in upland environments did little damage to non-target plant communities while adequately suppressing M. vimineum, but mowing was preferable in the wetland environment where the best permissible herbicide also suppresses the non-target plant community.
A buried seed study in the same three environments was used to parameterize population matrix models. Population parameters varied slightly between environments but did not result in different responses to the simulated herbicide scenarios. Biocontrol via a recently discovered pathogen was not sufficient to suppress population growth; however, it allowed a longer interval between herbicide applications in logged and roadside environment.
In conclusion, M. vimineum populations do respond to various environmental factors, at least in some instances responding as a beneficiary of ecological changes rather than a primary driver of change. The outcomes of M. vimineum suppression efforts are driven less by context-sensitive population dynamics than by the influence of environmental context on choice and efficacy of suppression tactics.