Early detection and rapid control of invasive species is generally the most successful and cost-effective method of preventing new invasions.  The success of such programs depends on the ability to predict where species are likely to invade. The habitat preferences of new invaders may differ along an invading front compared to a more established invasion. Therefore, data collected along an invading front should be the best predictor for future new invasions. Microstegium vimineum (Japanese stiltgrass) is a relatively new invader in Indiana and the Midwest. It was recognized as a problematic species only ten years ago, and since then has become one of the most aggressive and rapidly progressing invasive species in the state. Microstegium invades forest understories and spreads rapidly along roads, trails, streams, and lake edges. We are monitoring the occurrence of new Microstegium invasions (< 5 years old) along the current northern boundary of its range, and incorporating these data into spatially-explicit GIS models to predict future spread of Microstegium, particularly in relation to landscape features that affect dispersal (e.g. lakes, streams, roads, trails) and natural and anthropogenic disturbances that affect the probability of establishment (e.g. treefall gaps, logging).  

Results/Conclusions

We found that most new Microstegium patches occurred on cooler east- and north-facing slopes with very few plants on west- and south-facing slopes. Increased light (measured as sky-view factor from hemispherical canopy photos) was strongly correlated with plant density, biomass, and seed production. However, with high light and dry soil conditions, Microstegium does not grow well and senesces early with little seed production. We have also found that Microstegium requires litter disturbance to establish and typically does not invade from dense roadside populations into undisturbed forests without such disturbance. We are currently combining our empirical data into spatial models that will generate predictions about areas that are most likely to be invaded and should help focus early detection programs to help slow the spread of this species, and also will provide an example of criteria that are important for the spread of other invasive species.