Increasing calls suggest integrating ecological theory into invasive species research, and we use this approach with Microstegium vimineum, an invasive grass in the U.S. that overruns native vegetation in forest understories. Whereas its abundance along roadsides and waterways is taken to indicate that these are dispersal corridors for its propagules, and we confirm the association, we investigate its stage-specific performance as a function of environmental drivers to elucidate a more detailed understanding of its niche requirements. Our study involved a two-tiered, observational approach. We first surveyed M. vimineum across forested and unforested habitats along a 100-km regional gradient from mountains to flatland. This is a common approach for investigating invasive species distributions, but niche differentiation is based on environmental requirements not location. For this reason, we conducted the second tier of our research by measuring stage-specific M. vimineum parameters (cover, biomass and reproduction) as functions of direct rather than proximal environmental drivers (light, litter cover, soil moisture and temperature) in paired invaded and uninvaded plots.

Results/Conclusions

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 provide the most suitable habitat. The environmental drivers in these habitats are strongly linked with M. vimineum performance: plant establishment increases with soil moisture and temperature, but is hindered by leaf litter; growth increases with diffuse light and soil moisture; and reproductive output only responds to increased light. The strong differences in performance between forest interior and edge habitats (waterway, road) suggest M. vimineum distributions may encompass source/sink population dynamics where high-sunlight edge populations provide source propagules for forest interior sinks. Our results demonstrate that a widespread invader has marked niche requirements at local and regional scales within apparently homogeneous monocultures. We show that an ecological approach – in this case niche theory – identifies key resource limits in an invasive species that can direct control and eradication efforts toward vulnerabilities in its life history. Instead of broad-scale control efforts, these data can target management toward putative source populations within what otherwise appear as single invasions.