Botanical Notes from Dr Evans’ Coastal Ecology Program on Sapelo Island
This Spring Break, we trekked to Sapelo Island, Georgia with Dr. Evans for an intensive, week long course entitled Coastal Ecology and Conservation. Sapelo Island is reached by a short ferry ride and has a rich history filled with Native Americans, plantation owners, the Hog Hammock Community whose inhabitants are known as Gullah-Geechees and a strong tradition of ecological research at the University of Georgia Marine Institute, where we stayed. A highlight of the course was a canoe trip out to Little Blackbeard Island, Georgia’s newest barrier island created when a new inlet was formed during Hurricane Irma last fall. During our week-long program on the island, we explored the ecology of the sand dune, salt marsh and maritime forest communities and got to experience the unique plant species associated with these habitats. The following paragraphs, written by students in the course, represent just some of the plants on the island and their fascinating characteristics.
Southern magnolia (Magnolia grandiflora) has been a long-standing presence in the maritime forests of the Southern coastal plain and barrier islands. Larger magnolia specimens on these islands are typically found in older forests and act as an indicator of forests that have experienced less extensive human disturbance. On Sapelo Island, we found many large magnolias in old growth forests on the northeastern portion of the island. These old growth forests are characterized by an uneven soil microtopography and an extensive palmetto understory, both signs that they had never been cleared for agriculture. These magnolia trees also offer ecological benefits through the production of large annual, compound fruit in the form of an aggregate of follicles. Wildlife such as birds, squirrels, and rabbits take advantage of and eat this annual seed crop. Small mammals and birds will also use its large, twisting canopy as cover and habitat as well. However, even with an obvious canopy presence of magnolia and copious seed production, there was no recruitment in the understory that would lead to a new cohort of trees. Possible explanations for this could be over browsing by deer populations. This lack of recruitment might present a problem for the future of Southern magnolia in the maritime forest of Sapelo island.
Old growth live oak trees are an ethereal presence to anyone that comes across them, like ancient giants, dripping with Spanish moss and furry with resurrection fern. Their branches, huge and curving, reach wide, some almost as big as the main trunk, giving the short tree a squat and solid appearance. Southern live oaks (Quercus virginiana) are one of the many species of evergreen oaks grouped together under the name live oak. Live oak acorns are an important food source for wildlife, and their thick branches are host to bird nests and epiphytes. Epiphytes are plants, such as Spanish moss and resurrection fern, that grow on other plants, but are not parasitic, and derive all their nutrients from the water that drips off the branches and leaves. On Sapelo, the live oak trees can be found all over the island, but some of the most awe inspiring live oaks are in ancient old growth patches of maritime forests, where they share the canopy with giant magnolia trees, and an understory of saw palmetto, which grows clonally, slowing snaking along the forest floor to create giant patches. They can also be seen in secondary growth forests that were once cotton fields where live oaks were left for slaves to take shelter from the harsh midday sun. These shade trees can be recognized by their distinctive open growth pattern, from when they were growing without anything around them to impede their outward growth. Live oaks are no longer commercially logged, but their wood is incredibly strong and was once important for ship building before the age of steel hulls, their thick branches and short trunks used for curved parts of the ship’s hull.
Zanthoxylum clava-herculis, also known as the toothache tree, Hercules’ club, or the southern prickly ash, is a tree na
is is found in dry, open dune ridges. Z. clava-herculis’ common names provide some insight into its most distinct and noteworthy traits. The name of toothache tree is derived from a common folk use of the tree. When chewed, the leaves produce a rather potent anesthetic which was used by native peoples, as well as early settlers, to treat toothaches due to the mouth-numbing effects. Our class got to experience this strange sensation! The names Hercules’s club and southern prickly ash refers to the unique bark structures which are found on this tree. Hundreds of spikes protrude from the stem, likely an adaptation to prevent herbivory. However there is no species within Z. clava-herculis’ range which both has the ability to be significantly detrimental to the success of the tree and would be deterred by such defences. This suggests that whatever animal drove this adaptation has since gone extinct.
For our class research project, we studied the invasion history of chinese tallow (Triadeca sebifera) across a chronosequence of dune ridges on the south end of Sapelo. Tallow was introduced into this country from eastern Asia for the utilization of its waxy fruits in the manufacture of candles and soap. Its rapid growth, high fecundity, stress tolerance, persistent seed bank, and root sprouting make it an aggressive invader in coastal systems of the SE US, where tallow has been shown to transform open herbaceous or shrub communities into a closed canopy forests. Tallow appears to have become established on Sapelo by the early 1980s following the last major hurricane, where over the last 30 years it has transformed dune and swale communities into tallow monocultures.