Non-native plant invasion modulated by land-use history and contemporary landscape patterns in the southern Appalachians
Some non-native invasive plant species are well suited for spread in forest-dominated landscapes and may pose a threat to forest communities. We determined the local and regional factors which the distribution of such species, in order to better understand the invasion process and to identify areas that are particularly susceptible to invasion. We conducted roadside surveys to determine the presence/absence and abundance of 15 non-native plant species known to invade forests in western North Carolina. We used linear and generalized linear models to examine how contemporary land use, landscape context, land use history, and topography influenced the distribution of the 15 focal species at local and regional scales. The most commonly encountered species were Microstegium vimineum (in 84% of plots), Rosa multiflora (in 69% of plots), Lonicera japonica (in 58% of plots), Celastrus orbiculatus (in 53% of plots), Ligustrum sinense (in 31% of plots), and Dioscorea oppositifolia (in 17% of plots). At the regional scale, distance to city center was the most important explanatory variable, with species more likely present and more abundant in watersheds closer to Asheville, NC. Many of the focal species were also more frequently encountered in watersheds at lower elevation and with fragmented forest cover. At the local scale, elevation was important for explaining the presence/absence of species, but less so for explaining their abundance. Forest cover and land-use history were the most important explanatory variables at the local scale. In general, species were more likely present and in greater abundance in plots with less forest cover and a higher proportion of area reforested since the 1940s. A notable exception was M. vimineum, which had higher abundance in plots with greater forest cover and more residential development. Our results underscore the importance of considering multiple spatial scales to understand the factors driving non-native plant invasion, and the need to consider both the contemporary landscape and historic land uses in facilitating invasion.