The forestlands of the southern United States are representative of ecosystems whose unique native flora and fauna are threatened by invasive plant species. Chinese tallow tree, tallowtree, or popcorn tree (Triadica sebifera (L.) Small) is an aggressive deciduous invasive tree that is forming monocultures throughout the southeastern United States and has become naturalized from the Gulf Coast of Texas to the Atlantic Coast of North Carolina. We present an approach for predicting future range expansion of Chinese tallow in forestlands of east Texas and Louisiana that integrates statistical forecasting and analytical techniques within a spatially-explicit, agent-based, simulation framework. Drawing on extensive data from the U. S. Forest Service (Forest Inventory and Analysis dataset, Non-native Invasive Plants dataset) and the U.S. Geological Survey (Land Use and Land Cover dataset), we apply this approach to identify where new invasions are most likely to occur, and to forecast the probable speed and geographical extent of range expansion over the next two decades.
Results indicate that Chinese tallow invasion is more likely in low areas, flat areas, and areas adjacent to water bodies and roads, and less likely in mature forest stands and stands in which there has been artificial regeneration (e.g., forestry plantations). Forecasted annual invasions advanced from the Gulf Coast of Texas and Louisiana northward and westward as much as 300 km, the most severe invasions occurring along rivers and other permanent inland water sources. In terms of total area invaded over the course of two decades, this represents an increase from <1 to about 7.5 percent of all forestlands (≈ 1.58 million hectares). Such time series projections of annual range expansions should provide land managers and restoration practitioners with an invasion chronology upon which to base proactive management plans.