d. Analysis of Data . Species lists have been compiled for all belts 

 sampled on Nauset Spit. Field data were transferred to tables in order to 

 correlate belt maps with quantitative vegetation information. Percent cover, 

 percent frequency, relative cover, and relative frequency were calculated for 

 each belt. Cover classes were converted to an appropriate percentage of 25 to 

 correlate cover class with point-intercept information- 



Species diversity was calculated for each site, using Simpson's index 

 (Table 56). This index indicated that species diversity increases very 

 rapidly following an overwash. Belt J, which overwashed in February 1978, 

 had an extremely low species diversity index (0.0052) since only Anmophila 

 breviligulata was able to recover from burial in the area. belts X (0.3540) 

 and Y (0.0767), stabilized by the U.S. Army Corps of Engineers within the 

 last 10 years, also had very low species diversity indexes reflecting the 

 selection pressure of rapid vertical accretion. Belts older than 10 years 

 did not differ markedly from one another in relation to age, even when drift- 

 line species, wore common in recently developed areas, were not considered. 

 Species richness was low in very recent areas, but as with species diversity, 

 it did net show pronounced trends in belts older Chan 10 years (Table 56). 



Table 56. Species number and diversity index 

 for each belt site on Norti: Beach. 



40 to 92 







yrs old 







D 





38 



H 

 I 





26 

 45 



Approx. 



26 





yrs old 







Less Chan 

 10 vrs old 



Diversity 



0.7 457 

 0.3285 

 0.8596 

 0.7358 

 0.7842 

 0.6205 



0.8606 

 0.4739 

 0.8375 



0.7463 

 0.7751 



0.0052 

 0.1035 

 0.3540 

 0.0767 



1/2. 

 A prominence value (relative cover x relative frequency ) was calculated 



for each species within each belt. The prominence value (Disraeli and Fonda, 



1979) weights favored larger plants, which presumably have greater community 



importance. A similarity matrix was constructed using a modification of the 



Gleason similarity index: 



208 



'?f X 



