Traces of the Ancients in the Lower Suwannee Region Part V. Shell Mound: Mysteries and Speculations

We’ve learned a great deal about how ancient Native Americans used Shell Mound as an important pilgrimage site, but questions still remain. Among mysteries are the motivations for erecting the huge mound, and functions that might have been served by its crescent form and partially enclosed ground-level space.

Some possible answers have already been posed, for example the mound may have afforded protection from storm surges and fires. And it may have been a kind of garden for growing useful plants. Another plausible suggestion is that full time occupants of a village may have lived in the ground-level plaza during the cold winter months where they were protected from frigid winds. They would move in the warmer months to the crest of the mound where exposure to breezes provided a partial respite from heat, humidity, and biting insects. The opening on one side of the crescent may have provided access, obviating the need to scramble over piled up shells to reach the plaza.

 

This panoramic image made on November 19, 2017 shows most of the Shell Mound plaza, and the trees in the background conceal the greater part of the actual mound . The people are standing on the future trail that follows the inner perimeter of the mound. In this view the central area of the plaza appears to be depressed.

Maybe the following qualifies as rank speculation, but Shell Mound might have served a hydrologic function. Recall earlier discussions about the general scarcity of fresh water throughout the “blue desert.”

Shell Mound flooding on July 28, 2018. Flooding was much more extensive than indicated in this photo looking across the plaza, and several frogs were active in the water.

On July 28, 2018 Peg and I visited Shell Mound to photographically document sites planned for placement of informational panels along the trail. Our visit was not a success. In a few months the new section of the trail we had helped to lay out and clear had become overgrown by rank herbaceous vegetation. At times it was difficult to get a sense of whether we were actually on the trail. Biting insects were fierce as usual, and they kept us moving along. Rains had been unusually heavy and to our surprise, much of the amphitheater-like inner part of the complex—the plaza—was flooded, including major sections of the new trail. We avoided standing in the ankle-deep water to take photos, and even if we had done this, it would have been difficult to get an accurate perspective on placement of the panels.

Following are my notes made after we returned from the field:

The presence of apparently abundant frogs was perplexing. I wish I could have caught one to find out what species were present—from their behavior I guessed they were “pond frogs” (genus Lithobates, formerly Rana). And what could have brought them to Shell Mound? Amphibians are intolerant of saltwater and generally absent from sand dunes. So why are these frogs at the end of a dune extending a mile or more into the Gulf of Mexico—a place where standing fresh water is rare and ephemeral? It taxes the imagination to suppose that they all hopped the mile or more down from the other side of Dennis Creek in response to puddles forming in the past few weeks. Perhaps there is a permanent population here that persists in wet spots or burrows and explodes in numbers in the rare instances when heavy rains make conditions favorable by turning low spots into ponds. A permanent population of frogs at Shell Mound could be yet another artifact of the ecological changes brought about by its builders. It seems unlikely that ancient people would have intentionally brought frogs to the site, and that this frog population would have persisted for hundreds of years. Nevertheless, it seems clear that the ancients and their activities are no less responsible for the presence of frogs there today—without the people and the mound they built, freshwater ponds would not exist in this place. 

On another visit, Winter Solstice, December 21, 2018, almost the entire plaza was flooded. Tides had not been extraordinarily high, and it seems likely that the floodwaters were fresh.

 

Flooding of the Shell Mound plaza on  December 21, 2018. An informational panel placed along the trail can be seen in the upper left center of the image. Flooding persisted so that in late April 2019, refuge staff built an elevated boardwalk to keep this section of the trail passable.

Speculation can run amok, and the possible persistence of a population of frogs rekindles earlier vague notions about a possible hydrological function for the mound. In addition to its other services, might the mound have been a built as mechanism for capturing and retaining fresh water? Could there be a freshwater spring under the Shell Mound plaza, and the ancient people built the mound to protect it from inundation by tidewater? Or might the plaza be a purpose-built relatively impermeable basin capable of collecting and storing rainwater? Could the mound be part of a hydraulic system that raises the water table, effectively storing groundwater and releasing it to the plaza?

 

A tree-dimensional LIDAR image of Shell Mound developed by Dr. Sassaman and his cooperators. LIDAR accurately measures land elevation by penetrating vegetation. In this view looking North-Northwest the partially enclosed basin-like configuration of the plaza is evident.

Still curious, I revisited Shell Mound on December 22, 2020, wondering if I could find any patches of hydrophytic vegetation on the plaza that might denote a permanent seep or pool. Or were any burrows in evidence that could provide refuge for frogs during the dry season. Unlike on nearly the same date two years earlier, this time there was no flooding; the floor of the plaza seemed quite dry, although moister than the adjacent areas of sand dune. Nor was there any evidence of wetland vegetation or signs of burrows of crayfish or other animals. Onsite observations did make it clear, however, that the plaza is not a flat area as originally believed but is clearly a basin. If designed for something other than catching and retaining water, it has the problem of being flood prone. More thoughts about the frogs led to a reconsideration of my earlier hasty guess that they were probably pond frogs (genus Lithobates). Perhaps more plausibly they were spadefoot toads (genus Scaphiopus), frogs  that dig spiral burrows in loose soil, live most of their lives underground, and breed explosively in times of flood.

 If, as seems likely, the frogs I observed were Scaphiopus, the possibility of a permanent supply of fresh water under the plaza is much diminished. Nevertheless, as suggested in my notes from 2018, frogs would almost certainly be absent from this place were it not for the ancient inhabitants and the structure they built,

 

The images above were made December 22, 2020 and they illustrate the basin-like configuration of the Shell Mound Plaza. The top image was made from the open end of the crescent looking toward the west and the central area of the mound. The middle image looks to the east, back toward the opening of the crescent. Note the green vegetation in the central area surrounded by higher drier ground surrounding it. The lower image was made from roughly the same place as the middle one and looks toward the southeast where the boardwalk permits passage over an area of occasional deep water.

We’ll probably never run out of questions, but getting some more answers could be relatively easy. A hydrologist with appropriate skills could answer some of the questions about the possible role of the basin. And a herpetologist could collect and identify the frogs and offer possible explanations of how they got there or are able to persist.

 

Finding the Wicky

Field Notes: Lower Suwannee National Wildlife Refuge, June 3, 2019

This is another day in which Peg and I have been volunteering at the refuge welcome desk. During a break I hiked the entrance road out to the highway. The 1.4-mile round trip offers the opportunity to engage in wildlife viewing, and I record any new observations and post them on the iNaturalist database to help build a growing list of refuge biota.

This morning I observed some plants not previously reported from the refuge. Not far from the main building I noticed a blossoming yucca, later tentatively identified it as a weak-leaf yucca (Yucca flaccida). Two kinds of yuccas might occur here, and I will have to wait for review by an expert before I am sure about this identification. Then I saw several plants with large white blossoms and purplish centers. I thought they were hibiscuses but couldn’t get a good photo. Next, I photographed an engaging little plant I later identified as a marsh pink (Sabatia stellaris). Moving on, not far from the trail I spotted two of the big-blossomed plants I was unable to photograph earlier. Scrambling through bushes and getting snagged by brambles, I was rewarded by an excellent photo of the plants later identified as pineland hibiscus (Hibiscus aculeatus).

 

Marsh pink (Sabatia stellaris), upper image, and pineland hibiscus (Hisbiscus aculeatus), lower image. Both are common wildflowers of pine flatwoods.

 Continuing along the trail, I noticed a tiny blossoming shrub. Using the camera in my iPhone, which is good at close-ups, and bending toward a cluster of blossoms near the ground, I took a couple of shots. Back indoors at the refuge’s reception area and out of the bright sunlight, I got a first look at my photos. The ones made of that last plant provided a hint of recognition. “I know that plant,” was my first thought. And “What is it doing here?” was my second.

 

The tiny shrub first observed on June 3, 2019 on the Lower Suwannee National Wildlife Refuge's Tram Ridge Trail. The cluster of flowers is less than knee high (about 20 cm) above the ground, and each blossom is less than a half inch (1 cm) across.

Putting a jumble of thoughts together it dawned on me that this little shrub was another new species for the refuge list. The blossoms were distinctive and familiar, and ‘mountain laurel’ immediately came to mind. Mountain laurel (Kalmia latifolia) is a dramatic shrub I would expect to see on Appalachian mountainsides. The flowers of this new plant looked like mountain laurel, but it would be far out of place in our pine flatwoods. Nevertheless, the cup-like pale pink blossoms unmistakably said ‘mountain laurel’…or so I thought.

 

Stock image of the flowers of mountain laurel (Kalmia latifolia), a shrub commonly associated with Appalachian mountainsides.

Later consulting my guidebooks, I found that I was almost right. I easily identified the new little plant as Kalmia hirsuta, not the same species as mountain laurel, but in the same genus and in that sense a sibling.  As with many plants, this new one has multiple common names none of which is widely accepted as “correct.” It is sometimes called ‘Wicky,’ ‘Hairy Wicky,’ ‘Hairy Laurel,’ or ‘Sandhill Laurel.’ I regarded the wicky as the prize among the new plants I saw that day. Only later did it dawn on me that its distinctive flowers are tiny, and only a fraction of the size of those of mountain laurel. If the close-up hadn’t made them seem much larger in the photo than in life, I might not have made the connection. Regardless, finding a close relative of the familiar mountain laurel in pine flatwoods in the Florida peninsula was a surprise.

 

Flowers of the wicky, Kalmia hirsuta. Compare them with those of mountain laurel in the previous image. The close resemblance may be easy to miss because flowers of the wicky are many times smaller than those of mountain laurel and the low-growing plant tends to be much less conspicuous.

Another connection made discovery of the wicky intriguing. I was engaged in some informal research concerning the resemblance of landscapes of the Adirondack Mountains of northern New York State to those of the far north. Northern boreal (i.e. spruce-fir) forests circle the globe at high latitudes, and extend into parts of northeastern North America in only a few places, including the Adirondacks Two kinds of laurels may offer clues. Sheep laurel (Kalmia angustifolia) also known as ‘sheep kill’ because its foliage is poisonous to livestock) occurs in boggy areas in northeastern North America. Bog laurel (Kalmia polifolia) is a true northern species that occurs across Canada and a few northernmost parts of the United States and is regarded as an indicator of boreal forests.

After discovering the wicky, I wondered what southern pine flatwoods, Appalachian mountainsides, northeastern bogs, and boreal forests have in common that makes them attractive to this group of relatives in the genus Kalmia. The wicky and bog laurel seemed almost like bookends, anchoring the southern and northern North American limits of the laurel family.

The laurels are members of a large family of shrubs and small trees known as heaths (Family Ericaceae) that includes blueberries, huckleberries, staggerbushes, rhododendrons, azaleas, and others. Some of these are common across broad swatches of the east, others are restricted to certain habitats. In the north, at least, they are often found in boggy places.

So, how to explain the varied climates and landscapes that are attractive to the laurels and their relatives?  It didn’t take much research to dig up some clues. Heaths, including the species of Kalmia that drew my immediate attention are known to specialize in soils poor in nutrients. They have symbiotic mycorrhizal fungi in their roots which help to extract nutrients from poor soils and make them available to the plants which would otherwise be unable to absorb them. Nutrients in the soil are scarce in areas of the far north and in bogs where it is too cold or too wet, and slow to decompose dead materials become tied up as peat. They are also acidic, resulting in double jeopardy because acid soils make it difficult for plants to take up any free nutrients that might be present. Appalachian mountainsides may similarly be acidic and poor in nutrients owing to thin soils leached of nutrients by flowing water. Southern pine flatwoods and sand hills often have acidic soils and abundant rainfall may leach nutrients from them.

Before my discovery of the wicky deep in the south, I remained under the impression that heaths are primarily specialists of bogs and northern landscapes. I was aware that blueberries, staggerbushes, and other heaths are common in Florida flatwoods, sandhills, and scrub, but only after discovery of the wicky did it dawn on me that these plants are no less at home in these southern landscapes than they are in northern bogs. Their importance in flatwoods was underlined a week after discovery the wicky when I found one more interesting heath. Tarflower (Bejaria racemosa) is yet another common shrub of flatwoods. Named for its showy sticky flowers that trap insects, it has been speculated that the remains of ensnared insects fall to the ground and help the plants by releasing nutrients from their decomposing remains.

So, boreal forests, peat bogs, Appalachian mountainsides, and pine flatwoods are separated by latitude and topography and seem to have little in common. Nevertheless, they share challenging soils in which the Kalmias and other heaths, including blueberries, huckleberries, tarflower, and others can thrive.