Dune 



Communities 



Solt -Mofsh 

 Communities 



Figure 39. Two-dimensional ordination of Nauset Spit-Eastham 

 vegetation data. 



are associated with the salt-marsh grouping; salt marshes affected bv deep 

 overwash burial (site 3-F-78, site l-F-77, and site l-F-78) are associated 

 with the dune or drift-line grouping. Dunes affected by overwash burial 

 (site 3-T-78 and site l-T-78) are also associated with the duse or drift-line 

 grouping. 



Elevation data for both sites i and 3 were tied to a local USGS bench eaark. 

 so that all site elevations couid ha coapared. Elevation Bean and range were 

 calculated for each of the 13 sites and super inposed on the two-dimensional 

 ordination (Fig. 40). With the exception of site 3-F-78, the dune grouping 

 elements are all located at higher elevations than the salt-marsh grouping 

 elements. The effect of overwaeh on sampled dunes was not only to lower the 

 mean elevation and range for each site, but also to maintain a supratid^l 

 elevation capable of sustaining a dune conffijunity. In sampled salt sarshes 

 that recovered from shallow burial, elevation raean and range were not raised 

 enough to make the sites supracidal. Dune or drift-line vegetation could not 

 withstand inundation, and salt-iaarsh plants were able to recover. In ssspled 

 salt marshes that were buried by asore than 34 centiseters of overwash sand, 

 elevation was raised enough to sustain a dune coontmlty. The one notable 

 exception is site 3-F-78 which by Nauset Spit-Eaathaa standards was still 

 within an lntertidal range, although an average of 72 centlsseters of eand was 

 deposited on ths site in 1978. Spring tides tlmt are generally lower during 

 the sususer then during the spring and fall enabled dune vegetation to survive 

 at low elevations. During the oussser of 1978, there were no major stosrss so 

 that these low-lying drift lines were not flooded by ths high tides. Dana 

 vegetation was able to grew at lo«ser elevations during that Brasses' than in 

 previous years. Most of the plants In site 3-F-7& were killed by saltwater 

 inundation in- 1979; a continuous dune cossnurtity did not form. 



88 





