The invasion of non-native species contributes to the modification of biogeochemical cycles, inhibition of natural regeneration of native species, and the loss of ecosystem biodiversity and productivity. Even though introduced in the early 1800s, Japanese honeysuckle (Lonicera japonica) was first recorded outside of cultivation along the Potomac River in 1882. The Japanese honeysuckle is a vigorous invader of the southeast United States. It experiences rapid growth, phenotypic plasticity for response to herbivore damage, leaf phenology, and plant growth form and structure, evergreen or semi-evergreen leaves, and early flowering for long durations. Hence, our objective is to understand the historical trend in range expansion of the Japanese honeysuckle and identify potential determinants of invasion. We documented the two most recent sets of field measurements of Japanese honeysuckle in southeast U.S. through Southern Nonnative Invasive Plant data Extraction Tool (SNIPET). We then compared the empirical results with predictions of existing models, which were based on less-recent data. Potential rate of spread was calculated using distance from the nearest known propagule source. We finally associated the SNIPET data with data from Forest Inventory and Analysis (FIA) using multiple linear regression to identify potential determinants of invasion.
Results/Conclusions
Our results indicate the Japanese honeysuckle generally spread southward. During the survey period, the number of sample plots in which Japanese honeysuckle was detected approximately increased 50% in number. Mean percent coverage of Japanese honeysuckle in sample plots increased significantly (P-value < 0.05) during this period. Our empirical results supported the general trend of southward expansion predicted by existing models, which were based on less-recent data. Our results of multiple linear regression suggested that the invasion of Japanese honeysuckle was positively associated with adjacency to water bodies, temperature and species diversity and negative associated with slope, forest stand age, distance to the nearest road, and fire disturbance. Our model provided important insights into the management of Japanese honeysuckle, which threatens to continue its invasion throughout southeastern U.S. forests, as well as other, recently invaded, areas. Armed with knowledge of current and potential future high risk areas and, hence, likely paths of invasion, forest managers can develop long term monitoring and control strategies for effectively slowing range expansion and mitigating its effects.