The Vegetation of South Padre Island, Texas in Relation to Topography

Abstract

Vegetation patterns were studied in relation to topography to ascer- tain the degree of phytosociological change and to provide an inventory of the vegetation of South Padre Island. Six major terrestrial topographic zones were recognized: (1) Foreshore, (2) Backshore, (3) Primary dunes, (4) Secondary dunes and vegetated flats, (5) Tidal flats, and (6) Washovers. The flora includes at least 204 species of angiosperms representing 47 families. Five families, Compositae (26), Cyperaceae (10), Gramineae (46), Leguminosae (24), and Scrophulariaceae (8), account for 55.9% of the species diversity. The vegetation occurs in distinct zones that correspond closely to topographic facets. Comparison of three trans-island transects showed that Schizachyrium scroparium was dominant on all three tran- sects and the only important species which occurred on all three transects. Real estate developments have produced major changes and development is continuing. Thus, the natural habitat of South Padre Island may rapidily disappear. Padre Island is the world's longest barrier island. It extends 182 km along the Gulf Coast of Texas from Corpus Christi on the north to Brazos-Santiago Pass at Port Isabel on the south (Andrews 1971). Islands of similar geologic origin occur north as far as Galveston Bay and south to Altimira, Tamaulipas, Mexico, about 402 km south of Brownsville, Cameron County, Texas. Padre Island varies from about 450 m to approximately 4.8 km in width and is separated from the Texas mainland by the Laguna Madre, a shallow estuary having a maximum width of about 16 km. South Padre Island is separated from the northern two-thirds of the island by the Port Mansfield Channel. Padre Island is unique in that it provides an essentially uniform environment extending 182 km along the Texas coast; however, infor- mation on its vegetation and plant ecology is meager. Hedgepeth (1953) discussed the geologic formation of barrier islands off the Texas coast and the composition and sorting of beach sands on these islands. He also commented briefly on the flora and fauna of the beach zone. Thorne (1954) discussed the distribution of maritime flowering plants of the margin of the Gulf of Mexico and emphasized that the flora and vegetation of the perimeter of the gulf was inadequately known.