Vegetational analysis and floristics of four communities in the big ball hill region of Padre Island National Seashore

摘要

Vegetation of the Big Ball Hill region of Padre Island National Seashore was sampled using 100-m transect lines within each of four communities during four sampling periods in 1996 and 1997. Importance values of plant species and community richness, evenness, and diversity were determined. Seventy genera and 83 species of flowering plants were identified. These occur in 33 families with the Poaceae (17 species), Asteraceae (11 species), Cyperaceae (8 species), and Fabaceae (6 species) most common. The Big Ball Hill flora contains Flaveria brownii and Spowbolus tharpii, which are endemics of the western Gulf barrier islands. Lycium carolinianurn var. quadrifidura, reported only along bayshores in Texas, was found in the tidal flat community. Plant community structure was quantified and the following profile for the Big Ball Hill region is proposed: 1) a bare foreshore primarily due to human disturbance, 2) a backshore, with much bare ground often due to human disturbance, vegetation dominated by Uniola paniculata, 3) a primary dune ridge supporting Ipomoea imperati and U. paniculata as dominants on the windward side and U. paniculata, Heterotheca subaxillaris, and Paspalum monostachyum dominant on the leeward side, 4) a zone of secondary dunes or vegetated fiats, or a mosaic of both with Schizachyrium scoparium var. littorale codominant with P. monostachyum, and 5) a tidal flat that is largely bare but which supports typical halophytic vegetation including Blutaparon vermiculare, Limonium carolinianurn, Machaeranthera phyllocephala, Monanthochloe littoralis, Salicornia virginica, and Sporobolus virginicus. Compared to results of earlier vegetation studies on the island, these communities are less diverse and appear to be recovering from previous overgrazing.