Callery pear invasion in prairie restorations is predicted by proximity to forest edge, not species richness.

In the American Midwest, grasslands are highly diverse, endangered ecosystems that require conservation and restoration because they face the threat of plant species invasions. Pyrus calleryana (Decne.; Rosaceae) is a particularly problematic invasive tree in these ecosystems and relatively little is known about the factors that dictate its success. Landscape features regulate the spread of some invasive plants and may play an important role in dictating the vulnerability of grasslands to P. calleryana invasion. Towards developing a predictive framework for grassland invasion, we performed a fine-scale spatial assessment of invaded and uninvaded prairies to determine if landscape characteristics including proximity to forest edge, roads or residences, plant communities or soil characteristics could be used to predict P. calleryana invasion. We found increased invasion near forest edges, likely due to bird dispersal and optimal foraging habitats. Within invaded prairies, P. calleryana was prevalent where there was lower ground cover by grasses and forbs and where there was limited organic matter but increased soil phosphorus, nitrate and micronutrients. This study could not determine if P. calleryana caused these changes or if it established because these parameters were favorable. Our data also indicated an intriguing relationship of increased species richness in P. calleryana invaded sites, potentially because uninvaded sites were characterized by dominant grasses that may reduce available niche space. Taken together, this work suggests that P. calleryana establishment depends on the relative propagule pressure and niche availability and indicates potential for developing a predictive framework for landscape invasion. [ABSTRACT FROM AUTHOR]