Coevolution of Landscape and Culture: The Vegetation of Indian Shell Mounds in Florida's Ten Thousand Islands

Borel, Joan

This study evaluated changes in vegetation which resulted from the activities of prehistoric peoples in the Turner River drainage, Collier County. Botanical and archaeobotanical field surveys were used to quantify differences between the plant communities of anthropogenic shell mound islands and the natural wetland surroundings. Interacting vegetation-forming factors of elevation, climate, water salinity, substrate, and human impacts were isolated and evaluated through hypothesis testing. Objectives were to assess the human factor in the evolution of southwest Florida's landscapes and the environmental factor in the evolution of the complex Calusa confederation. A total of 185 plant species was recorded at 15 survey sites, including two coastal shell mounds, four freshwater mounds, seven natural areas along Turner River, and two Tamiami Trail Mikasuki villages. At eight of these sites, stratified random sampling was used to collect presence/absence data on the plant species found within 44 circular sample areas (11.3 m radius). The presence/absence matrix was analyzed by TWINSPAN, a multivariate sorting program. Classification of samples clearly demarcated plant communities of coastal mounds from both freshwater mounds and natural areas. Classification of species gave four main floristic groups: 1} tropical tidal mangrove communities, 2) warm-temperate freshwater swamps, 3) tropical West Indian hardwood hammock communities (on both coastal and freshwater shell mounds), and 4) a mixed group of tropical hammock and temperate species, normally of a more northern distribution (mainly on freshwater shell mounds). The mangrove and freshwater swamp communities are interpreted as being natural communities (not determined by shell mound construction), whereas the tropical hardwood hammock and mixed hammock/temperate species are "derived" communities, of mainly anthropogenic origin, determined in part by theintroduction of plant species of economic use by the Native Americans who inhabited the shell mounds. People were present in southwest Florida over 12,000 years ago, while modern ecosystems are only about 5,000 years old. These wetland landscapes were modified by human cultures, which were shaped by environmental opportunities and challenges requiring cooperation and organization.