Multivariate analysis of invasive plant species distributions in southern US forests.
Context: Invasive plants cause significant impacts in forested areas throughout the world. However, little is known about the relative importance of environmental drivers on the establishment and spread of invasive plants across forests at broader spatial scales. Objectives We evaluated which factors are more closely associated with successful plant invasions across southern United States (US) forests and predicted regional susceptibility to invasion by 16 known major invasive plant taxa. Methods We compiled environmental variables and presence-absence data for invasive plants across 52,690 southern US forestland plots surveyed by the Forest Inventory and Analysis (FIA) program of the USDA Forest Service. We used an ensemble species distribution modeling approach to model the potential distribution of the invasive plants and evaluated effects of the environmental predictors on species occurrences. Results Invasive species presence was favored by proximity to land use such as pastures, croplands, and developed areas, as well as by high light availability and soil capacity to retain nutrients and water. Soil organic matter was negatively correlated with invasive species presence. However, the effect of climatic variables and other soil properties, such as pH and soil depth, was species-specific. Conclusions Climate, land use, and soil organic matter were important but varied in their influence on invasive species distributions. Our results also indicate that most of our focal invasive plants are likely to occupy large forested areas throughout the study region. Thus, estimates of invasion risk should be incorporated into conservation strategies to prevent further establishment of invasive plants in forested areas.