Effect of wrack accumulation on salt marsh vegetation, Baruch Institute, Georgetown County, South Carolina

Abstract

In March 2004, four arrays in different types of salt marsh vegetation were covered with 15-20 cm of wrack secured in place, in an attempt to duplicate the natural deposition of wrack on the marsh by tides and storms, and to quantify and extend anecdotal observations and the results of previous studies. A control plot in each array was left uncovered; another plot was covered with only 2-3 cm. The wrack was removed from one plot in each array at one, two, four and seven month intervals. One month of wrack coverage appeared to have little effect on either density or standing crop, recorded seven months after initial covering, of the principal marsh species. Above ground parts of these species, with the exception of Spartina patens and Borrichia frutescens, appeared to be killed or extremely inhibited after two months of wrack coverage or longer. Wrack 2-3 cm thick (never removed) appeared to have inhibited the marsh species after seven months, but not as much as the 15-20 cm wrack mat. These results are fairly consistent with those of an earlier study at Jamaica Bay Wildlife Refuge, New York City, that focused on responses to wrack of Spartina alterniflora only, except that two months' coverage seemed necessary to kill back most of the S. alterniflora in that study. However, in another study at Jamaica Bay encompassing several species and vegetation types, most species declined gradually with increased length of wrack coverage over a six-month period. Future studies will focus on recovery of the vegetation once the wrack has been removed, and on chemical changes in the soil caused by the decaying wrack, which may in turn affect the future course of vegetation development.