Study Shows Stiltgrass Invasion May Facilitate Invasion by Garlic Mustard

Photo by S. Luke Flory

New results provide experimental evidence that an initial plant invasion associated with suppression of resident species and increased resource availability can facilitate a secondary invasion. Such positive interactions among species with similar habitat requirements, but offset phenologies, may exacerbate invasions and their impacts on native ecosystems.

A study conducted by S. Luke Flory and Jonathan Bauer used a long-term field experiment to test for indirect facilitation by Microstegium vimineum (stiltgrass) on a secondary invasion of Alliaria petiolata (garlic mustard). These species represent two of the most widespread and problematic invasive plant species in eastern North America. They found that Alliaria produced seven times more biomass and nearly five times more fruit in plots that had previously been invaded by Microstegium­. In addition, Microstegium-invaded plots had substantially less resident biomass than controls, and very little Microstegium early in the growing season when Alliaria is most productive, presumably due to the direct effects of Microstegium in prior years. 

Photo by S. Luke Flory

The study experimentally demonstrates that Microstegium can facilitate Alliaria across a range of disturbance regimes. Greater growth and reproduction of Alliaria in Microstegium-invaded plots may be indirectly facilitated by Microstegium’s suppression of shared resident competitors and associated increases in resource availability, although other mechanisms are possible. Understanding how direct and indirect interactions among species, particularly non-native invasive species, might structure communities is a primary need in ecology.

Photo by S. Luke Flory

For a copy of the full article email S. Luke Flory.