Resilience of Seacoast Bluestem Barrier Island Communities

by F. W. Judd, Univ of Texas-Pan American, United States,
R. I. Lonard, Univ of Texas-Pan American, United States,
J. H. Everitt, Univ of Texas-Pan American, United States,
D. E. Escobar, Univ of Texas-Pan American, United States,
R. Davis, Univ of Texas-Pan American, United States,



Document Type: Proceeding Paper

Part of: Coastal Zone '91

Abstract: Natural disturbance is an important force in population and community dynamics and barrier islands are paradigms of disturbance dominated ecosystems. They are formed, shaped, and moved by hurricanes. During overwash events large expanses of vegetation are either uprooted, covered with sand, or inundated with saltwater. The Secondary Dunes and Vegetated Flats zone is the broadest (600-700 m) topographic zone on South Padre Island, Texas. The dunes of this zone are partially to completely stabilized and seacoast bluestem Schizachyrium scoparium, is the dominant species. We initiated studies in May 1986 to investigate resilience of seacoast bluestem communities on South Padre Island to simulated hurricane effects. In a vegetation removal experiment, the re-establishment of cover was 39.4% per year. At this rate complete recovery would require about 31 months. Species richness was not fully restored in 27 months, but seacoast bluestem was the dominant species on the removal plots at termination of the experiment. Rate of recovery of vegetation in sand coverage experiments was markedly slower: 12% (10 cm), 9% (20 cm), and 6% (30 cm) per year. Species richness was restored within 9 months in the 10 and 30 cm sand coverage treatments and seacoast bluestem was the dominant species on all treatment plots at termination of the experiment. Saltwater exposure had only the slight effect of killing the leaves of Cassia fasiculata on some treatment plots. Species richness was not affected by the saltwater exposure and seacoast bluestem was the dominant species throughout the experiments. The estimate of cover using SPOT satellite imagery was too coarse to be useful, but CIR aerial photography offers great promise as a way to census total island vegetative cover.

Subject Headings: Barrier islands | Vegetation | Dunes | Salt water | Hurricanes and typhoons | Aerial photography | Sandy soils | North America | Texas | United States

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