Our Shell Mound and others in the southeast are significant archaeological features, and they also have created biological environments unlike any others on our coastlines. And it seems likely that the Ancient people who built them and relied directly on nature and its bounty understood the values of these new environmental features.
On an early visit to Shell Mound, I spotted a curious looking small tree with large, vaguely walnut-like compound leaves with long, dark green crenelated leaflets, I identified it as soapberry, Sapindus saponaria. Found on shell mounds, among other habitats, an extract of its fruits has soap-like qualities useful as a cleansing agent. Later I learned that their soapy extract is a potent fish toxin (but harmless to people), and various cultures have used this quality in related plants to capture fish. People washing clothes along the shore might have discovered paralyzed fishes floating on the surface nearby. We’ll probably never know if Shell Mound’s people discovered this use, but the thought is tantalizing. And might ancient inhabitants having learned of this, carried the plants from one occupied site to another?
Soapberry tree on Shell Mound, showing the berries that contain a substance that is a natural detergent and also a potent fish toxin.
By 2018 a new set of interpretive panels was being developed by Dr. Sassaman and his students to tell the recently unraveled and much richer story of Shell Mound. A rerouted trail with signs points out significant sites, taking visitors through the process of discovery. A long section of trail had no signs to inform visitors and seemed to be a good opportunity to include a panel telling of the unique vegetation. I took on the task of developing the vegetation panel.
Originally identified as saffron plum (Sideroxylon celastrinum), this plant is probably instead an individual of its common relative, gum bully (S. lanuginosum).
Snowberry (Chiococca alba) is a low-growing, almost vine-like shrub that specializes in shell mounds. I looked for the iconic saffron plum (Sideroxylon celastrinum) and didn’t find it, but the related gum bully (S. lanuginosum) is much in evidence, and clearly is adapted to the conditions provided by Shell Mound. Summer grape (Vitis aestivalis) thrives on the mound. Two kinds of cacti with edible fruits were discovered including the shell mound cactus (Opuntia stricta) and the common and widespread devil’s-tongue (O. humifusa). Collaborator Collete Jacono and I discovered Florida swampprivet (Forestiera segregata), another species commonly found on shell mounds. Climbing buckthorn (Sageretia minutiflora), a plant frequent on shell mounds in the southeast may have been used for its rattan-like vines. Many common and widespread plants occur on Shell Mound, but a significant subset of these same plants do not occur in adjacent habitats or in any place close to the edge of the Gulf.
Summer grape (upper image) and a cactus (Genus Opuntia--lower image) on Shell Mound. Grapes are uncommon in most of the coastal habitats surrounding the mound, and the fruits of cacti are edible. Together with grapes, they provide a source of sugary food rarely found in coastal regions.
Red cedar (Juniperus virginiana) was of interest because it is abundant on Shell Mound, was used by Native Americans, and became important in the economic development of the area after the arrival of Europeans. Red cedars occur from southern Canada throughout eastern North America and invade tall grass prairies in Kansas and Nebraska. Growing in abandoned fields, on the edges of fresh- and saltwater marshes, and in waste places, they tolerate droughts, floods, and occasional saltwater inundation. In few places are they as abundant as in the Cedar Keys, however, and pencil manufacturers in New York City turned to the Cedar Keys to supply red cedar wood for their product because of their unusual abundance on the islands and adjacent mainland. Thriving in well-drained neutral or alkaline soils, they are vulnerable to fire, and Florida habitats least prone to fires are islands and shell mounds.
This redcedar near the pinnacle of Shell Mound may be hundreds of years old. As with many plants that are intolerant of shade, leaves comprising the thin canopy are clustered near the top.
Location, topography, and vegetation all interact to make Shell Mound practically invulnerable to fire and a safer site for a village than any nearby locations. This and other factors probably made Shell Mound an attractive place to live and to visit for hundreds of years. It protected residents from floods and fires, its elevation provided protection from winter winds and summer heat, and its thick mantle of vegetation provided deeper shade than anywhere else along the coastline. It may also have served as a kind of garden, supporting the growth of useful plants like red cedar, soapberry, climbing buckthorn, shell mound cactus, and surely other plants whose uses we do not know. Some of the plants on Shell Mound may occur there now simply because they benefit from its growing conditions, or their arrival may have resulted from actions of people, who modified and improved their environment by carrying useful plants from site to site.
It is also possible that the biological community supported by Shell Mound may have affected the people who built it in ways that encouraged them to enlarge the mound. They may have been motivated to continue building once they realized the role of Shell Mound in supporting useful plants.
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