Human alterations of the environment may interact with natural disturbances to alter the characteristics of biological communities in unexpected ways. I studied vegetation plots in a leveed bottomland hardwood forest at Bayou Sauvage National Wildlife Refuge near New Orleans, LA to determine how Hurricane Katrina affected the woody plant community and the distribution of the invasive Chinese tallow tree (Triadica sebifera). The storm killed approximately 68% of all trees in both overstory and understory and reduced basal area proportionately. Nearly all mortality was due to storm surge flooding, which was trapped for up to 3 wk by levees surrounding the refuge. Mortality was far greater than observed in other recent Gulf hurricanes and was three times higher than in similar forests in the nearby Pearl River basin that were struck by the highest winds from Hurricane Katrina. Flood mortality resulted in reduced community diversity and increased the dominance of the introduced T. sebifera after the storm at the expense of less flood-tolerant native species. The plant community appears likely to shift from a canopy dominated by native species to one dominated by Chinese tallow. This shift appears to be largely an unintended consequence of levee construction, which prevented storm surge from rapidly draining after the hurricane passed. The results suggest that widespread floodplain development may interact with future hurricanes to produce abrupt shifts in plant community composition and function in coastal habitats throughout the southeastern United States.
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Vol. 168 • No. 1