Effects of man on the shore vegetation of Biscayne Bay

Teas, Howard; Wanless, Harold; Chardon, Roland

The shoreline vegetation of Biscayne Bay has suffered from man's activities since the turn of the century. Shore vegetation has been eliminated in much of north Biscayne Bay and has been seriously impacted even along the relatively less polluted and altered south Biscayne Bay. A vegetation history has been reconstructed for five sites: Interama; Cocoplum; Saga; Section 33 of T56, R40; and Card Point. The study has involved on-site biological and geological investigations and made use of historical accounts, maps and aerial photographs. The effects of man are basically of two types: (a) physical, which includes land fill; vegetation removal and erosion by boat wakes, and (b) water quality and quantity factors. Drainage of the Everglades that began about 1900 lowered the water table and affected all five sites. With reduced freshwater sheet flow the high and storm tides made the marl soils saline farther upland and eliminated freshwater vegetation. Building of roads and dikes that restricted overland freshwater flow further accentuated salinity problems. Mosquito control and agricultural drainage ditches allowed saline bay waters to penetrate and seed mangroves in marl areas that had been freshwater marsh. Near Card Point the saltwater zone has extended 2 to almost 4 miles inland. One section of coastal land, Section 33 of T56, R40, has mangroves growing on more than 300 acres of former marchland because of the upland advance of salinity in drainage ditches and the elimination of freshwater sheet flow by dikes. In several areas, mangroves are currently growing on land that had been vegetable fields before salinization of the soils. It is possible, because of this invasion of marshlands by mangroves, that there is a greater acreage of mangroves along Biscayne Bay today than there was in 1990, although much of the mangrove area that has been seeded has developed into stunted, scrubby growth because of the marl soil. Studies of the mangrove communities that have developed on marl marshlands are needed in order to learn more about their ecological role, nutrient status and potential management. Also needed are more experiments with mangrove planting and ecosystem reconstruction. Abstract provided by author.