Fire effects on post-invasion spread of Chinese tallow (Triadica sebifera) in wet pine flatwood ecosystems in the southeastern United States

Abstract

Prescribed fire has been increasingly used in restoring endangered slash pine (Pinus elliottii) flatwood ecosystems in the southeastern United States. We collected overstory and understory data to study the impact of fire on the post-invasion spread of Chinese tallow tree (Triadica sebifera) in a wet slash pine flatwood in the Grand Bay National Wildlife Refuge, Mississippi, USA. A total of 70 contiguous 30-m2 quadrats were installed and measured prior to fire (2018) and remeasured post-fire (2019 and 2020) to study the spatial distribution of the tallow soil seedbank and seedling recruitment. In addition, the same data were collected around 11 randomly selected tallow seed trees with varying burn intensities (estimated by stem-bark char heights) to evaluate the changes in seedling recruitment and survial by burn intensity. Soil tallow seedbanks around seed trees (427.7 ± 43.9 seeds m−2) were significantly greater than elsewhere (34.6 ± 13.2 seeds m−2) (p < 0.001). Tallow’s soil seedbank varied spatially with more tallow seeds confined in areas with low elevation, canopy closure, and grass cover. Tallow seedling density was negatively correlated with litter and shrub cover; seedling recruitment rates increased with fire intensity with the mean seedling:seed ratio averaging 0.25 in burned areas, significantly higher than that in unburned areas (0.01–0.02). However, most germinants died by the end of the second year, resulting in nonsignificant differences in the density and height of surviving seedlings between burned and unburned areas. These findings suggest that prescribed fire is an effective management tool for depleting the tallow seedbank while not contributing to post-invasion spread.