Effect of wrack accumulation on salt marsh vegetation, Jamaica Bay Wildlife Refuge, New York City, New York

摘要

In April 2004, five arrays in different types of salt marsh vegetation were covered with 15-20cm 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 2-3cm. The wrack was removed from one plot in each array at one, two, four, and six month intervals. Up to two months of wrack coverage appeared to have little effect on either density or standing crop (recorded six months after initial coverage) of the principal marsh species, Spartina alterniflora, S. patens, Distichlis spicata, Juncus gerardii, and marsh margin Phragmites australis. Except for Phragmites, however, these species appeared to be strongly inhibited after four months of continual coverage, and killed or extremely inhibited after six months. Wrack 2-3cm thick (never removed) appeared to inhibit the aforementioned species after six months, but not as much as the 15-20cm wrack mat. These results are fairly consistent with those of an earlier study that focused on Spartina alterniflora only, except that two months' coverage seemed sufficient to kill back most of the S. alterniflora in that study. Phragmites apparent resistance to wrack cover can be explained by the considerable energy reserves of its large rhizomes and the ability of its awl-like shoots to penetrate a thick wrack mat. Future studies should 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.