Florida's Natural Habitats Part 4 -Indian Shell Mounds are their own Habitat Type

Indian Shell Mounds are their own Habitat Type

The Natural Communities listed previously from the Florida Natural Areas Inventory are undisturbed, and non-transitional. They are not mixed between two habitats, nor are they in transition from one habitat type to another. As found in the field, habitats are seldom pristine examples, but listing the variants here would extrapolate the list to over 181 habitats. Simplicity and brevity were key in this citizen-scientist guide to aid in initial understanding of the basic habitat types. There is one transitional type of habitat that needs to be considered due to its historical context and wide distribution in Florida. The  Shell Mound Habitat is a transition habitat unique to native American midden mounds.

Shell mounds are small hills, usually in coastal locations, composed entirely of shells (clams, oysters, whelks) discarded by generations of Native Americans which support an assemblage of calciphilic plant species. Archeological evidence indicates they were occupied at the time Europeans first landed in Florida. Several are now surrounded by mangroves, evidence that they were built when sea level was lower than today. Originally there were many such shell mounds along coastal lagoons and at the mouths of rivers (and even inland along the St. Johns River), but most were destroyed for road building in the early part of the last century.

A rich calcareous soil develops on the deposited shells which supports a diverse hardwood forest on undisturbed mounds. Central Florida mounds are often characterized by tropical species occurring north of their normal range. On Turtle Mound at Canaveral National Seashore in Volusia County tropical trees such as white stopper, sea torchwood, wild lime, false mastic, inkwood, and lancewood were recorded at or near their northern range limits in 1971. Freezes occurring since then have eliminated or reduced the populations of many of these by the time the mound was re-sampled several decades later, illustrating that the tropical flora of these northern mounds is in constant flux. Shell mounds on the Cedar Keys in Levy County on the Gulf coast are also northern outposts for tropical species most likely brought in by migrating birds. Tropical species found on these Keys such as white stopper, Florida swampprivet, snowberry, and saffron plum are all species whose fruits are eaten by migrating birds. Shell mounds in the Florida Panhandle, i.e. on St. Vincent Island and on St. Joseph peninsula, support temperate canopy trees such as live oak and cabbage palm as well as calcium-loving temperate species not found in nearby maritime hammocks on sand, including soapberry and Carolina buckthorn. 

Even south of Tampa and Cape Canaveral, the species composition of shell mound forests tends to be more strictly tropical than that of maritime hammocks on sandy substrates in the same region, with white stopper, Florida swampprivet, strangler fig, saffron plum, and gumbo limbo being the most commonly encountered woody species. 

Shell mound habitats are found along the coast throughout Florida and range westward and northward along the coastlines of the southeastern U.S. In the 1920s botanist John Kunkel Small noted the tropical flora on large shell mounds at Port Orange (1922), Hobe Sound (1922), Horti Point on the south end of Merritt Island, Marco Island, and at the mouths of the Sebastian River, Crystal River, and Caloosahatchee River. As mentioned, most of these were destroyed for road building. Three of the mounds Small described, Turtle and Green Mounds near New Smyrna and Madira Bickel Mound near Tampa Bay, are preserved in State or Federal parks. Others are features in larger parks, including St. Joseph Bay State Buffer Preserve, Cedar Keys National Wildlife Refuge, Cayo Costa State Park, Charlotte Harbor Preserve State Park, Ding Darling National Wildlife Refuge, and Coconut Point Park.

The uniquely tropical flora of Central Florida shell mounds is in constant flux, with species being periodically exterminated by freezes and subsequently re-colonizing, most likely via bird dispersal. North Florida shell mounds have some temperate hammock species such as live oak and cabbage palm, plus calcium-loving temperate species such as soapberry, Carolina buckthorn, and sugarberry. Central Florida shell mounds may have a combination of tropical and temperate canopy species with tropical understory species, including white stopper, snowberry, and marlberry. Further south shell mounds have a predominantly tropical flora in both the canopy and understory. Shell mounds may have vegetation similar to tropical or temperate types of maritime hammock, but differ in that they grow on pure shells rather than sand or sand mixed with shell fragments. 

Soil disturbance on shell mounds from old home sites, clearings, potholes from illegal digging, etc. can allow exotic species such as Brazilian pepper and Australian Pine to invade. They require patrolling to prevent further loss of the historical resource. 

Exemplary Sites include Canaveral National Seashore (Turtle Mound; Volusia County), Tomoka State Park (Volusia County), Green Mound Archaeological Site (Volusia County), Cedar Keys National Wildlife Refuge (North Key; Levy County), Madira Bickel Mound State Archeological Site (Manatee County), Mound Key Archeological State Park (Lee County.

 This is part four of a series on Florida Natural Habitats. See:
Part One of this Series


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