(30) Invasion of Chinese tallow (Triadica sebifera) along a dune chronosequence on Sapelo Island, GA

Seed dispersal and population response to disturbance are drivers of invasive plant species distribution. Coastal dune communities experience a high frequency of disturbance, such as associated with hurricanes, making them... [ view full abstract ]

Seed dispersal and population response to disturbance are drivers of invasive plant species distribution. Coastal dune communities experience a high frequency of disturbance, such as associated with hurricanes, making them susceptible to invasion by non-native species. Chinese tallow (Triadica sebifera), a bird dispersed tree species has successfully invaded a chronosequence of dune ridges and swales on the south end of Sapelo Island, Georgia. Tallow became established on Sapelo in the early 1980s following the last major hurricane.   Since that time, tallow’s rapid growth, high fecundity, stress tolerance, persistent seed bank, and root sprouting has allowed it to transform open dune and swale communities into closed canopy, forest monocultures.  Its establishment tracked the spread of the native shrub, Morella cerifera within the swale and dune slope topographic positions within the chronosequence.  Despite its purported salt salt tolerance, we found that the two hurricanes that hit the island in 2016 and 2017 resulted in extensive tallow mortality due to salt water flood and overwash disturbance.  We hypothesized that the current distribution of tallow is now restricted to a specific topographic position associated with the dune slope. Transects were established along the swales, slopes, and ridges of dunes with three replicates spatially separated by disturbance type.  GPS points, mortality, and status were recorded for every chinese tallow present, and cores were taken from living tallow stems in the transects. Seedling presence was counted along transects. Additionally, soil samples were collected to examine the tallow seed bank. We found a pattern of near complete mortality within the swale, in contrast to high survivorship on the dune slopes. Very few tallow were present on the dune ridges.  Despite an active seed rain, the absence of tallow on dune ridges may be a function of the absence of Morella in this habitat. Morella promotes the establishment of tallow both by modifying soil properties and serving as a beacon for seed dispersal.  Mortality of tallow in the swale was associated with repeated flooding by salt salt water during the hurricanes. This mortality event compressed the tallow population into distinctive, linear belts along the dune slope.