Traces of the Ancients in the Lower Suwannee Region Part IV. Shell Mound: Ecology

 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.

Traces of the Ancients in the Lower Suwannee Region Part III. Shell Mound: The Story

 

Enter Dr. Ken Sassaman and his students from the University of Florida’s Laboratory of Southeastern Archaeology. Shell Mound became a subject of intense study in 2013. To learn the detailed story about Shell Mound, visit the site and follow the marked trail that explains the significance of the mound to ancient peoples. Accounts of the story are also available on the Friends of Refuges website, the Laboratory of Southeastern Archaeology website, and in various writings by Dr. Sassaman. The following only touches on some of the highlights.

  

Initial findings indicated that the mound was not seriously altered by removal of shells for road construction as formerly believed, but instead was purposefully built amphitheater-like, with a rounded level spot open on one side that Sassaman calls “the plaza.” The crescent-shaped mound was more than a simple refuse heap, and multiple lines of evidence indicate that not only was it deliberately built, but at one time was partially rebuilt.

 

 

Schematic of Shell Mound developed to orient visitors to the walking tour. The stippled areas are open water or salt marsh, the white area is part of a large sand dune, and the crescent shaped mound is shaded light gray. The open area on the southeast (lower right) part of the mound was previously thought to have resulted from removal of shell for road building.

What I thought looked like a causeway was the arm of an ancient sand dune. Strong prevailing winds during the ice ages produced massive parabolic (U-shaped) dunes, orienting the arms of the “U” in southwest to northeast directions. Shell Mound is at the tip of one of those dune arms, which is aligned with Palmetto Mound, the island site of the ancient cemetery.

 

Google Earth image of Shell Mound (lower left) and the "causeway" leading to it. Although the mound is obscured by vegetation, the "plaza" is seen as an open area. A small part of Hog Island, site of Palmetto Mound, is seen at the far left, partially covered by the label for the observation deck.

 

The alignment of Shell Mound, the archaeologists realized, has cosmological significance. From there the sun is seen setting behind the cemetery on Hog Island's Palmetto Mound on the winter solstice—the shortest day of the year and rising toward the landward origin of the dune arm on the summer solstice—the longest day of the year. Ancient southeastern Native American cultures drew spiritual strength from remains of their ancestors, and saw the movement of the sun at the winter solstice as its symbolic entry into the underworld where their ancestors dwelt, and the summer solstice as its reentry into the world of the living. The march of the changing seasons as seen from Shell Mound mirrored the progression of the years and connected the generations.

 

 

Shell Mound, December 21, 2018. The sun is seen setting behind Hog Island, site of the cemetery on Palmetto Mound on a cloudy and cold Winter Solstice.

Excavations revealed that Shell Mound served as a gathering place for pilgrims from throughout Florida and the southeast. Visitors celebrated the summer solstice when the sun emerged from the underworld and began its arc toward the cemetery on Palmetto Mound, symbolizing and sustaining connections between the living and the dead. This world view may be related to the Day of the Dead celebrations persisting in Mexico and Central America, said to stem from adaptation of a traditional Mayan summer festival to coincide with the Christian All Souls Day.

 

Sunrise seen from Shell Mound on Summer Solstice, June 21, 2020. The camera is looking northeast, back toward the origin of the dune arm.

Investigations showed that Shell Mound is much younger than formerly believed, having been completed only a few hundred years before the arrival of Europeans. The village was inhabited for less than 1,000 years by at most a few hundred people at a time, and abandoned about 650 A.D. Burials at Palmetto Mound continued until about 1,300 A.D., and materials from the cemetery have been dated as early as 500 B.C., a full 1,800 years earlier. Evidence that some burials in the area have been moved and reburied suggests that environmental events, including sea level fluctuations, caused people to move the relics of their ancestors to protect them from inundation and loss to the sea. Conceivably some sites were abandoned when inundated by rising seas, and re-occupied when the shoreline advanced or retreated.

 

We know little about the occupants of Shell Mound, and without the work of Dr. Sassaman and his students, we would know only that they left behind a huge pile of discarded shells. Questions often asked by visitors (What was their name—what tribe lived here? What did they look like? Where are they today?) have no informed answers. They must have had a name for themselves, they probably looked much like the Native Americas first encountered and described by Europeans, and although extinct as a people, some of their genes may persist in people alive today. More revealing information is now forever lost.

 

Traces of the Ancients in the Lower Suwannee Region: Part II. Shell Mound: The Structure

My first visit to the Shell Mound, a Unit of the Lower Suwannee National Wildlife Refuge, was sometime in July or August 1996. New to Florida and arriving at the absolute worst time of the year for a visit to any outdoor site in the state, Peg and I began to walk on the Dennis Creek trail, which is adjacent to the mound. Having covered less than a quarter mile in humid ninety-degree heat, we beat a hasty retreat back to the car, pursued by dive-bombing yellow flies and swarms of mosquitos.

We came back more than once. The interpretive signs indicated that the mound was essentially a Native American refuse heap consisting primarily of discarded oyster shells, and it was perhaps as much as 6,000 years old.  So huge a refuse heap seemed improbable. Maybe the mound provided a retreat to escape from storm surges; the site is close to sea level and far from any protected uplands.  The structure was said to have been altered in modern times, evidenced by a hollow spot on one side where shells were mined for use in road construction.  An ancient cemetery on nearby Hog Island was discovered more than a century ago, and in early decades was thoroughly looted by antiquities collectors.

 

 

Shell Mound from offshore. The launch ramp can be seen at the water's edge and the mound rises beyond.

No evidence of burials and no collectable artifacts were ever found on Shell Mound itself and it had no apparent purpose other than for waste disposal.  Despite its rather dull story, the mound is certainly a testament to the numbers and energy of the people who built it.

The foregoing was the story I carried with me for more than 10 years. Despite any real sense of mystery about Shell Mound, it was still an interesting visit. Close to Cedar Key, it was a place where one could connect easily with the unspoiled waters of the Gulf and nearby shoreline habitats. White pelicans, dolphins, and other charismatic wildlife are often on display, and in the right season, the Dennis Creek trail is an attraction for those interested in natural history.  However narrow or broad their interests, most visitors seemed to enjoy at least one trip to Shell Mound. 

At the end of the road near the boat launch and fishing pier, one can look back toward the land and see the namesake mound. The road curls around it on the way in, but anyone unaware of what to look for it might miss it. Visitors standing in front of it sometimes ask in puzzlement, “where’s the mound?” 

 

Trail leading up and over the summit of Shell Mound. Its structure of hard packed shells is evident where the vegetation has been worn away.

Decidedly un-mound like from most viewpoints, shell mound shows itself only as a thick clump of oaks and red cedar trees. But despite its modest appearance, at more than twenty feet above the surface here, it is one of the highest points on the entire Gulf of Mexico coast. Climbing on a well-worn packed shell path to the pinnacle provides an unparalleled view out over the marsh. Framed by branches of a live oaks (Quercus virginiana or Q. geminata), a small red cedar (Juniperus virginiana) and a gum bully (Sideroxylon lanuginose) shrub, one looks out over bands of pale green saltgrass (Distichlis spicata) in the foreground near the base of the mound, then farther out a thick gray expanse of black needlerush (Juncus roemerianus), a narrow light band of smooth cordgrass (Spartina alterniflora) at the water’s edge, and then to the blue waters of the Gulf beyond. Across the water lies a chain of narrow islands, one of which contains the ancient cemetery. Visitors inclined to linger during the warm season will be soon discovered by legions of hungry salt marsh mosquitoes (Aedes taeniorhynchus and A. sollicitans). Before fleeing, try to get a deep and almost visceral sense, not of how tall the mound is, but instead of the flatness of everything else, as far as the eye can see.

 

The view out over the Gulf of Mexico from the summit of Shell Mound. Zonation of marsh vegetation can be seen extending from from the base of the mound as the elevation decreases gradually.

Dramatic as the view from Shell Mound is, and as notable as is its unusual elevation, one cannot truly get a sense of the place without learning more. Its irregular shape makes it difficult to estimate volume, but the structure covers about five acres in all. At about 700 feet in one dimension and nearly 500 feet in the other, its total volume is approximately 150,000 cubic yards, or 4 million cubic feet. That computes to about 30 million gallons, so if its builders had carried up basket loads of oyster shells (it is made mostly oyster shells but also bones and other kinds of shells) holding about a gallon each, it would have taken them 30 million trips. Archaeologists have estimated that more than a billion shells make up the mound. Clearly the place wasn’t built in a day, and a series of major efforts surely went into its construction.

 

Hog Island viewed from the fishing pier on Shell Mound. This is actually a narrow chain of islands, one of which contains the ancient cemetery on Palmetto Mound. This island chain and Shell Mound were contiguous in times when sea level was lower than it is today.

Aerial photographs show Shell Mound at the end of a long formation that looks like a causeway. Had the ancients built not just the mound, but also constructed a three-quarter mile long causeway to reach it from the mainland? They would have invested a great deal of effort just to reach a waste site.

If enough people lived here to pile up so many shells, one wonders what they did about water. Did they carry fresh water from miles away to meet their daily needs? The Cedar Keys region has been called “the blue desert” because of remoteness from ready sources of fresh water. Each of us contemporary Americans uses between 80 and 100 gallons per day—if we had to carry all of it, we would be daily toting between 600 and 800 pounds. Surely the inhabitants of Shell Mound were able to get by with much less, but carrying the heavy stuff could be a problem, nevertheless. Collecting rainwater in huge pots might have helped but would not have sufficed during much of the year. Or maybe they found freshwater springs that empty into the marsh. Such springs are known at various places in the region, but not close to Shell Mound. Maybe the land area of Shell Mound is sufficient to support dug wells able to provide adequate fresh water. Most islands have fresh groundwater, because less dense fresh water “floats” on top of saline ground water. Trees and other terrestrial plants require fresh water, and their presence on islands indicates that some fresh water is available.

Tantalizing as these questions were, ready answers were elusive.