Invasion of Chinese Tallow along a dune chronosequence on Sapelo Island, Georgia

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Burress, George
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Scholarship Sewanee 2020 , Chinese tallow , Sapelo Island, Georgia , Coastal dune , Succession , Chronosequence , Invasive species , Hurricane disturbance
Chinese tallow, coastal dune, Sapelo island, succession, chronosequence, invasive species, hurricane disturbance Regimes of frequent disturbance facilitate the spread of invasive species. Hurricanes striking the southeastern U.S. coastline have facilitated the spread of the invasive Chinese Tallow Tree (Triadica sebifera). The succession of vegetation from fore-dune to rear-dune in coastal ecosystems can be understood through the dune chronosequence model. This analytical model shows that as new dunes accrete they shield older dune from environmental factors that can limit vegetative growth like salt spray and overwash. The pattern of vegetative succession in which plants are better established the further they are from the shore allows for a space for time substitution when analyzing these ecosystems. On Sapelo island, a barrier island on the Georgia coast, a dune chronosequence with forty years of Tallow growth experienced back to back years of hurricane disturbance in 2016 and 2017. Extended periods of salt water inundation from flooding, combined with extreme winds and sea swells during these hurricanes caused extensive mortality of Tallow. I hypothesized that Tallow survival and regeneration following this hurricane disturbance would be influenced by the depositional age along the chronosequence. Specifically regeneration would be facilitated by the presence of Morella cerifera along the chronosquence. Wax myrtle (Morella cerifera) acts as a perch for migrating neotropical passerines who disperse tallow seeds while feeding on the myrtle’s high calorie fruit. In 2018, 27 sites across three topographical areas on three different dunes were surveyed for the presence of seedlings, abundance of soil seed banks, the health and presence of adult Tallows, and soil nutrients in order to determine if the Tallow population was recovering from hurricane disturbance. In 2019 these sites were re-surveyed in order to determine if and where seedlings were maturing into saplings in order to learn more about what environmental conditions best support tallow regeneration. I found that the pattern of successful Tallow regeneration was determined by the proximity to the swale, the lowest topographical region of the dune where water and nutrients aggregate in the soil, and not by the age of the dune. Widespread invasion of Tallow into southeastern coastal ecosystems and its ability to persist through disturbance events will likely alter the structural composition of these dune environments. Restricted Tallow recovery in the middle in rear dunes has the potential to limit the utility of the chronosequence model in explaining patterns of succession if this invasive continues to dominate coastal ecosystems. The increased frequency of hurricanes due to global warming has the potential to accelerate the invasion of Tallow due this species resilience to disturbance in comparison to native species.