meters above MSL 



3 F 78 

 3 t 78 



1 I 77 



I r 77 



Up II 

 Hp77 

 1 f m 77 

 3 F 77 



Figure 40. Elevation of sites used in ordination (see Kig. 39). 



*** Disc ussion . Dunes that are eroded during overwash are recoionized by 

 dune vegetation by means of seeds and plant fragments regenerating in drift 

 piles found on was hover deposits and by rhizome extension from nearby remnant 

 dunes. In major was hover channels through the dune line, few drift piles are 

 found. Drift piles that are deposited in washover throats are principally 

 composed of large material (.either shrub fragments or i.«rge sections of 

 Armophila rhizomes torn from the dunes), which is difficult for overwash 

 surges to carry through the dune line. Anvnophita bfeviliaulata is the 

 principal colonizing species. The seedlings are seldom found In drift piles 

 in areas that have been dunes, because overwagh surges carry light material 

 through tne area toward the fan terminus. 



In the few dune areas not eroded by overwash, the posfstona community ia 

 very similar in composition to the original community. Increase in Anmophila 

 bveviiigulata biotaass has often been highly correlated with increases in the 

 amounts of aeollan sand deposition (Tansley, 1968; kanwell, 1975; Chapman, 

 197b). On accreting dunes, vegetation is undergoing selection for genotypes 

 capable of withstanding continual burial. Aeolian sand burial can occur 

 throughout the year when windspeeds exceed threshold values (approximately 24 

 kilometers per hour), while overwash burial occurs during a single storm. Both 

 depositional processes are, however, more similar at Nauset Spit when seasons 

 are considered. Sustained, high winds and accompanying sand transport are more 

 common during the winter, when dune vegetation is dormant. Aeolian sand 

 deposition of 50 centimeters or greater per year is comsson in the northeast 

 (Goldsmith, 1972). Dane species, principally Ammophila, sees to grow best in 

 the areas of high accretion. Overwash sand deposition in February 1978 also 



89 



8M£ZM^£?^E£^?^Z<:Zux y'^ZteK^l'llzz^Xr.:'^ s;-r^iffei^;:^^x«^i^fo *„uj^^m& j m^^mzszsi 



"\ •'. • • • / 



\ 7 \ 



\« 



' , f. 



