Long-term dynamics and impacts of Microstegium invasion in the Piedmont of New Jersey
I used data from a long-term, permanent plot study of old field succession in the Piedmont region of New Jersey to document the dynamics of Microstegium invasion and it’s impacts on the understory plant community. Interestingly, the data revealed a failed Microstegium invasion in the mid-1980s. Microstegium successfully invaded the site in the mid-1990s, moving out from the old growth forest into adjacent second growth habitats. Microstegium tended to invade higher diversity plots, but overall local controls on invasion were weak, with nearly all areas invaded within a few years. Invasion by Microstegium resulted in a loss of diversity in the understory community and a dramatic increase in total cover. To determine potential mechanisms of these impacts, a biofeedback experiment was conducted using a common understory species at the site, Eupatorium rugosum. The experiment showed dramatic variation among locations in the direction and magnitude of biofeedbacks on the test species, but these effects were never strongly inhibitory. Any biofeedbacks mediated by soil communities are likely to differ across sites. As allelopathy is often invoked as a mechanism of invasion impacts, a survey of non-native invasive species at the site was conducted using a simple bioassay. Microstegium was one of the most toxic species tested, with effects similar to those of another understory invasive herb, Alliaria petiolata. Phytotoxic effects may partly explain this invasive annual’s impacts on the plant community.