Environmental factors controlling the distribution of forbs on coastal foredunes in Cape Hatteras National Seashore

Shifting sand, which either buries the seeds or seedlings of dune forbs or carries them away, is responsible for the absence of forbs on the front of the foredune and in other zones accumulating sand regularly. Experimental work with the seedlings of six dune forbs showed that they can withstand burial by no more than 5 cm of sand and that their seeds can survive burial under only 1 to 16 cm, depending on the species. At least 20 to 30 cm of sand normally accumulates each winter in a zone subject to regular sand deposition. Salt spray plays a secondary role in preventing the establishment of forbs on the front of the foredune. It is responsible for the elimination of species which may occasionally escape burial during the winter months and which happen to be susceptible to salt spray injury. Measurements of soil moisture, soil nutrients, and soil temperatures indicate that these factors differ only slightly on the front, top, and back of the foredune. These three factors, then, appear to have little influence on the distribution of the forbs.