The spatial legacy of introduction: Celastrus orbiculatus in the southern Appalachians, USA.
A variety of abiotic, biotic, human and historic variables related to environmental suitability and propagule pressure determine the distribution of invasive plants in a landscape. Understanding the role of these variables for invasive species is challenging because environmental variables are often correlated, many invaders have broad ecological niches, and invasive distributions are often highly dynamic. We examined the role of environmental variables at multiple spatial scales on the distribution of an invasive vine Celastrus orbiculatus (Celastraceae) in the southern Appalachians, USA. Using existing and newly collected occurrence data, we constructed spatial generalized linear mixed models of C. orbiculatus occurrence in the whole region as well as the areas nearest (established zone) and farthest (pioneer zone) from the purported introduction locus. For the entire study region, distance from the introduction locus and terrain slope were negatively related to the probability of occurrence of C. orbiculatus. The model was highly discriminatory, with an area under the receiver-operating characteristic curve of 0.91. Distance from introduction locus and slope were also important in the models for the pioneer and established zones respectively. The pioneer zone model also indicated a negative relationship with elevation and the established zone model indicated a positive relationship with local topographic position, but these models were less discriminatory. Synthesis and applications. Distance from introduction locus was the most powerful variable examined, suggesting an enduring legacy of introduction for the current distribution of C. orbiculatus. The varying results in the three zones highlight the importance of accounting for both introduction history and uneven propagule pressure in studies of observed invasive species distributions. The observed relationships with distance and elevation suggest that land managers should prepare for C. orbiculatus to expand its distribution in the region over time and with a warming climate.