Models for Predicting the Risk of Naturalization of NonNative Woody Plants in Iowa

Nursery and landscape professionals have introduced many useful non-native woody plants for managed landscapes, but the potential exists for new introductions to escape from cultivation and become pests. The objective of this study was to develop a comprehensive strategy to assess the risk of naturalization of non-native woody plants in Iowa. We examined life-history traits and native distributions of 100 woody plant species, including 28 species known to naturalize in Iowa and 72 other species not known to naturalize in the state. We tested three approaches to predict naturalization of woody plants in Iowa: (1) direct application of a previously developed decision tree designed to predict naturalization on a continental scale within North America; (2) application of the continental model modified to include traits important on a regional scale, and (3) development of a new regional model that included a geographic-risk component along with life-history traits. Our modifications to the continental model and the new regional model all were more powerful than the unmodified, continental model, as measured by their ability to classify species (classification rate) based on risk of naturalization, without reducing accuracy, as measured by the frequency of misclassification (error rate). Classification rates ranged from 65% for the unmodified continental model to 90% for the modified continental model. Error rates varied from 6% for the new regional model to 20% for the unmodified continental model, including horticulturally limiting error rates of 4 to 17%, respectivel