Vegetation Colonization of Dredge Spoil on Perdido Key, Florida

Abstract

The vegetation colonizing dredge spoil is described from the first year following massive beach nourishment. Dredge spoil was deposited in late 1990 gulfward of mean high water on Perdido Key, a harrier Island off the coast of the Florida panhandle, for a distance of 8 km and averaging 150 m in width. A grid of permanent plots was used to measure density and cover of the colonizing species. With a density of 997 plants per ht in Summer 1991. Cakile constricta was the most abundant of ten species colonizing the dredge spoil. Other species with a density of more that 50 plants per ht were Uniola paniculata, lva imbruata, Panicum amarum, and Oenothera humifusa. Sand fencing 10 15 m below old mean high water increased the density of U. paniculata. Maps of C. constructa show that the highest densities were adjacent to and below the old mean high water. A new strand line of C. constricta that was establishing just above the new high water mark in May 1991 was lost following overwashing from late spring storms. Canonical Correspondence Analvsis was used to compare species cover data from plots on the dredge spoil to cover data from permanent plots on the main island and above the old mean high water. Vegetation in the first year of colonization most closely resembled a species-rich strand or low density developing dune vegetation. The precarious nature of the vegetation colonizing onto the dredge spoil during the first year following deposition indicates that additional dredge spoil deposition is not advisable for several years.