COS 262-2 - Spread and growth mechanisms of Chinese tallow (Triadica sebifera) trees in fire regulated slash pine (Pinus elliottii) flatwoods of the Gulf Coastal Plain, USA

Abstract: Chinese tallow invasion has become a serious ecological threat to the sustainable development of native forest ecosystems, especially for those disturbed forests in the Gulf Coastal Plain of the United States. Therefore, understanding the mechanisms of Chinese tallow invasion and establishment processes and evaluating the interactions between tallow invasion and native ecosystem resilience at stand level have become very important to native forest ecosystem management and restoration. In this study, the invasion and establishment process of Chinese tallow and the effects of prescribed fire and microtopography on those processes were studied by analyzing the invasibility filters of native forests (overstory composition and density, canopy closure, understory vegetation cover, and soil moisture), disturbances (prescribed fire, hurricane, and flood), and microtopography (elevation differences) in three large size plots of tallow infested stands (0.18 ha, 0.7 ha, and 0.1 ha) that established in 2016. Spatial analysis and modeling methods such as paired correlation function, rhohat function, and point process model were used to analyze the effects of microtopography and invasibility filters on the distribution patterns of tallow trees. Moreover, the multiple comparison test and t-test were used to evaluate the impact of interactions between prescribed fires and microtopography on the growth and abundance of tallow trees. The results of the spatial analysis indicate that within the forest stand, the low-elevation flooded areas have more tallow saplings and large trees that are clustered together and repelled with overstory pine trees compared to the high-elevation non-flooded areas. Overstory canopy closure, understory vegetation cover, distance to overstory trees, distance to rill, distance to habitat edge, and elevation are significant invasibility filters that could affect the distribution of tallow trees. Meanwhile, under the same prescribed fire regimes, tallow trees located at low elevation flooded areas have a lower burn probability (p< 0.01) than those in high-elevation non-flooded areas. With infrequently prescribed fires (burn interval ≥ 4 years), tallow trees have a higher probability (p< 0.01) to transfer from saplings to large trees (seed trees) within pine flatwood. However, when there are frequent burns (burn interval ≤ 2 years), the growth of tallow trees is limited at the sapling stage (shrub stage) without seed production at high-elevation non-flooded areas because of high fire intensity compared to low-elevation flooded areas.