Predicting the potential range expansion of the invasive Lonicera japonica in the United States under current and future climate conditions

Background/Question/Methods Ecological niche models are valuable tools in predicting the potential range expansion of invasive species. Japanese honeysuckle (Lonicera japonica Thunb.), a native of China, Japan, and Korea, has rapidly expanded across the United States since its introduction in the early 1800's. With a range now covering most of the eastern portion of the U.S. and isolated pockets of the western U.S., L. japonica is currently recognized as an invasive species capable of severely limiting the diversity of native flora. While the spread of L. japonica has progressed seemingly unchecked up to this point, it is unclear if or where it will spread next. Using models to predict the potential range expansion of L. japonica will offer conservationists valuable insight into where to focus remediation and prevention efforts. Maxent, an ecological niche model, was used to project the present day potential range of L. japonica in the U.S. The model inferred where L. japonica is capable of growing by matching 19 WorldClim climate parameters with 143 coordinates corresponding to counties in China where herbarium records indicate the presence of L. japonica. A jack-knife was used to identify the climate parameters most indicative of L. japonica presence. Our jack-knife analysis was combined with our knowledge of the biology of the species to narrow the climate parameters used in our projections down to four: mean temperature of coldest quarter, minimum temperature of coldest month, mean temperature of driest quarter, and precipitation of warmest quarter. The model was also used to project the future potential range expansion of L. japonica in the U.S. using the IPCC future climate predictions.

Results/Conclusions The model's present day projection of the potential U.S. range is a close fit to the actual current range. The model does, however, predict that L. japonica may continue to spread westward into some untouched regions in the Texas panhandle, Oklahoma, and Nebraska and further northward in Indiana, Illinois, and Missouri. Prevention efforts should, therefore, be focused on these regions. The model's future projection indicates that under changing climate conditions the potential range of L. japonica will expand even farther beyond its present day limit.