The objective of this study was to determine whether patterns of native distributions of naturalized woody plants and their relationships to climatic analogs can serve as a sound basis to help identify high-and low-risk regions from which to introduce new woody plants to Iowa. We compared the native ranges of 28 non-native species naturalized in Iowa with those of 72 different, non-native species widely cultivated in Iowa, but with no record of naturalization. From this comparison, we tested two related hypotheses: (1) regions with the highest number of native species that have naturalized in Iowa have a significantly higher proportion of naturalizing species than predicted by the overall ratio of the number of naturalizing species to the total number of non-native species studied; and (2) regions identified as climatic analogs to Iowa conditions, based on important determinants of woody plant adaptation, have a significantly higher proportion of naturalizing species than predicted by the overall ratio of naturalizing species to the total number of non-native species studied. We discovered that the two regions with the highest number of naturalizing species (in southeastern Europe and northeastern China) have a significantly higher proportion of naturalizing species than would be predicted by chance alone. Two of the five regions identified as climatic analogs to Iowa conditions (in northeastern and central Asia) also displayed significantly higher proportions of naturalizing species, while a third (in southeastern Europe) was statistically significant only at the 10% level.

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Author notes

Journal Paper No. J-19581 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, Project No. 1018, and supported by Hatch Act and State of Iowa funds. The authors thank John Ambrose, Candice Gardner, Rick Lewandowski, Alan Meerow, Scott Schlarbaum, and two anonymous reviewers for their valuable critiques; Stephen Hendrix, Diana Horton, and Deborah Lewis for their assistance in accessing herbarium specimens; Ted Cochrane, Carol Foster, Warren Lamboy, James Phipps, Sandra Reed, Ken Robertson, Phil Rutter, Welby Smith, and John Wiersema for their assistance in locating native plant distributions; and Tom Hiett and Rex Heer for graphic arts assistance.

2Horticulturist.

3Associate Professor, Department of Horticulture, Iowa State University, Ames, IA 50011-1100.