PS 11-138 - Invasion of Callery pear (Pyrus calleryana) in grasslands of the American Midwest creates an awful predicament

Abstract: Callery pear (Pyrus calleryana) is an invasive plant that threatens ecosystems in the eastern United States. In this poster, we synthesize findings of several studies completed as part of our multi-pronged research program aimed at (a) understanding the profile of traits that facilitate invasion of this species, (b) assessing ecological effects during invasion and (c) developing restoration techniques in invaded habitats. To study invasive traits we observed leaf development on P. calleryana and native trees in grasslands near Dayton, Ohio, USA. We discovered that P. calleryana has an extended leaf duration as compared to native species with significantly earlier leaf out in the spring and later leaf drop in the fall. During this study, we also found that P. calleryana is more resistant to a late frost than co-occurring native species. To test of allelopathic potential, we monitored seed germination of native grassland species when exposed to exudates from P. calleryana as compared to a control. We discovered that leaf exudates suppress the germination of native species. For example, we found drastic (and significant P < 0.05) reductions in Coreopsis lanceolata germination when the seeds were exposed to leaf exudates as compared to the control. In the area of ecosystem effects, we measured soil enzyme activity under P. calleryana stems that had been cut and were resprouting as compared to intact trees. We found strong evidence of soil microbial activity, and that activity is enhanced in stems that have been cut and are sprouting as compared to intact stems. Finally, with regard to restoration, we experimentally cut P. calleryana stems in invaded grasslands and treated the stumps with prescribed fire, freezing (with liquid nitrogen) and herbicide application and assessed sprout response and survivorship. Results generally indicated that disturbance processes were totally ineffective at controlling P. calleryana and only direct applications of herbicide prevented sprouting. Intriguingly, we found that, in some cases, prescribed fire created a statistically significant increase in sprout numbers in relationship to the control (P = 0.036). This indicates that applying prescribed fire to invaded grasslands may exacerbate the invasion process rather than slow it. Overall, this compendium of active research projects suggests that P. calleryana invasion presents a vexing quandary: this tree possesses a suite of traits that facilitates invasion, that invasion creates a significant threat to biodiversity, and the control options are highly limited. Much work is needed to resolve this pear predicament.