Niche limitations of a vigorous exotic invader, Microstegium vimineum, across temperate forest ecotones
Robert Warren, Yale University

Niche limitations of a vigorous exotic invader, Microstegium vimineum, across temperate forest ecotones

We investigate the ecology and niche requirements of Microstegium vimineum, an invasive grass in the U.S. that overruns native vegetation in forest understories. We examine M. vimineum’s stage-specific performance as a function of environmental drivers across forested and unforested habitats along a 100-km regional and climatic gradient. We survey M. vimineum across the gradient and then measure stage-specific M. vimineum parameters as functions of direct environmental drivers in paired invaded and uninvaded plots. Lastly, we experimentally investigate recruitment per environmental drivers using plots with intact and removed litter substrate arrayed across our gradient. We find that all habitats are not equally suitable for M. vimineum – even those within which it occurs – and that the environmental conditions associated with roadsides and waterways are most suitable. The environmental drivers in these habitats are strongly linked with M. vimineum performance: plant establishment is hindered by leaf litter, growth correlates with overall herbaceous coverage and reproductive output increases with temperature and light. Litter substrate is an effective barrier to germination success, and dispersal is facilitated by flooding. Our results demonstrate that a widespread invader has marked niche requirements at local and regional scales within apparently homogeneous monocultures. We identify key resource limits that can direct management efforts toward life history vulnerabilities. The strong performance differences between forest interior and edge habitats suggest M. vimineum distributions may encompass source/sink population dynamics where sunny edge populations provide source propagules for forest interior sinks, with waterways providing a key dispersal link.