(c) WashoverFlats. Major washover areas exhibit a somewhat 

 different means of stabilization than small-scale features. In general, wash- 

 over flats are subject to overwash tor many years, since rhizome invasion from 

 adjacent dunes and salt marshes is not effective in stabilizing a large area 

 rapidly because there is a high ratio of barren area to perimeter. The prin- 

 cipal means of colonization of these major features is through the development 

 of dunes from drift lines. The large size washover flats and great deposi- 

 tional thicknesses provide an abundant source of sand to the developing dune 

 line. Since these flats are not rapidly stabilized, overwash frequently 

 occurs depositing new sand between and bayward of developing dunes. New dunes 

 are established toward the bayward edge of large washovers in association with 

 drift lines deposited in arcuate lines by bay-side storm surges and spring 

 tides. Since a large distance (typically 100 to 200 meters) exists between 

 the newly developing dune and the shoreline, onshore winds also contribute to 

 dune building. 



After dunes are well established, Ammophila bveviligulata rhizomes spread 

 seaward colonizing the barren washover. Complete recovery of a washover 

 occurs when the frontal edge of the new dune merges with the adjacent back, 

 dunes and the barrier profile is increased above the overwash threshold, 

 liarrier environments are translocated several hundred meters landward in a 

 quantum fashion by means of overwash and subsequent dune recovery with all 

 ecological units retained intact. 



III. VEGETATIVE RESPONSE TO OVERWASH 



1 . Introduction . 



The response of sand-dune and salt-marsh vegetation to overwash burial was 

 studied on Nauset Spit-Easthais. Research was divided into three parts: plant 

 community response to overwash, response of individual species to overwash, 

 and colonization of washovers. Initial research plans were designed to com- 

 pare the response of vegetation on washovers that were created at different 

 times. After the 1978 storm, the direction of the research changed since all 

 three sites chosen for study had been severely overwashed. 



Comparisons of species lists for northeast barrier beaches suggest that 

 the vegetation of Nauset Spit-Easthaia is representative of typical northeast 

 barrier beach communities during very early stages of succession (Table 4). 

 Thirty-three species were present on tnis section of the spit in 1977. This 

 compared to 242 species on Plum Island, Massachusetts, (Ahles, 1973) and 117 on 

 Honomoy Island, Massachusetts, (Moiil, 1969). Only three wel 1 -developed plant 

 communities have been present on the spit since the first aerial photos were 

 taken in 1938 — a dune community and high and low marsh communities. A sand 

 road, in use since 1922, devides salt-marsh communities from dune communities 

 along the length of Liu- spit. Two other discernible, early success ional com- 

 munities are present—the drift-line community and the ecotone between the high 

 marsh and dune community. Shrubs, notably fiyrica pensyivanica (bayberry), 

 Primus maritima (beach plum), and Rosa rugosa. (salt spray rose), are present 

 on Nauset Spit-Easthain but do not constitute a shrub community. Of the 21 

 marshes surveyed in a study comparing salt-marsh productivity in New England, 

 Nauset-Eastham ranked seventh (Godfrey and Travis, 1976). Few well-defined 

 communities, low species number, and high productivity are all characteristic 

 of sand-dune or salt-marsh areas that are either very young or highly stressed. 



59 





