Asian Bittersweet (Celastrus orbiculatus) Occurrence at Coarse and Fine Scales in North Carolina and Virginia

Asian bittersweet ( Celastrus orbiculatus ) is a widespread, invasive, twining vine in eastern North American forests. Factors associated with its local occurrence are well known but seldom reported at geographic scales coarser than research locations. We evaluated its occurrence across a hierarchy of land units ranging from coarse (provinces), intermediate (landscapes), and fine (site) scales in North Carolina and Virginia. Chi-square tests indicated a significant difference in the proportion of plots with C. orbiculatus in mountain (5.5%) compared to piedmont (9.9%) provinces. Using groups of forest types (e.g., Acer-Betula, Quercus-Pinus ) to represent landscape-scale land units, C. orbiculatus occurred in a greater proportion of plots classified as Quercus-Carya . At the fine scale of sample sites within landscapes, in plots where C. orbiculatus was present the soil moisture regime was classified as mesic significantly more often than xeric in both provinces. Foliage cover differed between mountain (9.6%) and piedmont provinces (5.1%), and among several forest type groups at the landscape scale but responded weakly to moisture regime. Our results show that the proportional occurrence of C. orbiculatus varied significantly among land units at each hierarchical level. We suggest that our land units, defined by physiography, tree communities and soil moisture regime, represent tentative eco-systems that can be included as spatial variables in models to improve predictions of the presence of C. orbiculatus , for example in response to a changing climate.