Considerable insight into what fosters a successful biological invasion can be gained by monitoring the initial stages of population establishment and growth. In 2003 we planted thirty patches of the invasive annual Microstegium vimineum (Japanese stiltgrass) into different habitat types within a forested landscape in central Pennsylvania. Recruitment, seed production, and spatial spread were quantified in each patch until they were eradicated in July 2006. We hypothesized that patch growth would be significantly different between habitat types, providing insight into which communities are most invasible by this species.
In general patches in the roadside habitat experienced highest recruitment and seed production, while most populations under intact forest canopy declined. Patch growth in wet meadow and disturbed forest habitats was intermediate. However, these differences were not statistically significant due to extremely high within-habitat variation in patch population metrics. As it became clear that Microstegium patches were not responding strongly to habitat type, we used multiple regression to explore the effects of small-scale environmental variables on recruitment and seed production. Results show that small-scale factors such as surrounding vegetation and soil chemistry have a significant influence on the success of Microstegium. Changes in population growth trajectories in reponse to small-scale environmental changes imply that habitat susceptibility to invasion by this species is not static.