Despite the large literature documenting the negative effects of invasive grasses, we lack an understanding of the drivers of their habitat suitability, especially for shade-tolerant species that do not respond positively to canopy disturbance. We aimed to understand the environmental niche and potential spatial distribution of a relatively new invasive species, wavyleaf basketgrass (Oplismenus undulatifolius (Ard.) Roem. & Schult, WLBG) by leveraging data available at two different spatial scales in the Mid-Atlantic region of the United States. We used maximum entropy modeling (Maxent) to predict the habitat suitability of this species at the regional and the landscape scale. Following variable evaluation, model calibration, and model evaluation, final models were created using 1,000 replicates. For each final model, we also investigated the contribution of each environmental predictor and the relationships between each predictor and predicted presence of our species.
Results/Conclusions
At the regional scale, our best models show that suitability for WLBG was driven by relatively high annual mean temperatures, low temperature seasonality and monthly range, low slope, and high cumulative normalized difference vegetation index (NDVI). At the landscape scale, suitability was highest near roads and streams, far from trails, at low elevations, in sandy, moist soil, and in areas with high NDVI. When comparing our results to an earlier Maxent model for this species, we found that the prediction for highly suitable habitat was over three times higher than previously. Overall, we found that invasion potential of this relatively new invader appears high in productive, mesic habitats at low slope and elevations. At the regional scale, our model predicted areas of suitable habitat far outside areas where WLBG has been reported, including large portions of Virginia and West Virginia, suggests serious potential for spread. However, large portions of this area carry a high extrapolation risk and should therefore be interpreted with caution. In contrast, at the landscape level, the suitability of WLBG is largely restricted to areas near current presence points, suggesting that the expansion risk of this species within Shenandoah National Park is somewhat limited.