and their modal elevations and then selected the "indicator," or dominant, species for the 

 TUckerton and Great Bay Boulevard marshes according to the following steps: 



1) Interpolate elevations, at 7.5 m (25 ft) horizontal increments, along each transect. 



2) Based on the "distribution of species" graphs (Appendix 3-A) for each transect, 

 determine what species are found, at 25-ft horizontal increments, along each transect. 



3) If the total number of occurrences is greater than ten for any given species, construct a 

 frequency histogram for that species. From the histogram, determine the modal 

 elevation for that species. 



4) If the total number of occurrences is less than eleven for any species, determine the 

 modal elevation by graphically averaging the transect cross-section. 



We prepared frequency histograms for six species and tidal range combinations having a 

 sufficient number of data points (Appendix 3-A). We also computed the mean elevation and 

 corresponding standard deviation for all species. After weighting the "percentage occurrence" or 

 percentage of transects covered by all species, we compiled a summary, or composite list. Table 

 3-2 gives the results by tidal range for each portion of the study area. 



The dominant plant was S. alterniflora in both tidal-range zones, with the short variety 

 covering 49-77 percent of the composite transects. Its modal elevation (86.6-99.1 cm [2.81-3.25 

 ft], Table 3-2) in the Tuckerton Marsh was similar to that in the Great Bay Boulevard marsh 

 despite a difference in mean high water of over 15 cm (0.5 ft). In fact, the mode was reversed for 

 the lower tidal-range marsh, being slightly above the Great Bay Boulevard marsh elevation. One 

 would expect just the opposite, since high-marsh elevation normally increases with tidal range. 

 Since the difference is subtle here, we believe it may be due to the altered drainage of the 

 TUckerton marsh, which is dissected by numerous ditches. Mosquito-control ditches or similar 

 features increase circulation and may also impound water over the marsh, possibly elevating 

 mean water levels or increasing the duration of flooding. A subtle change such as this could alter 

 flooding frequency and displace marsh habitats upward. Unfortunately, there is no way to confirm 

 this hypothesis for the Tuckerton marsh. However, we believe the difference is real for the present 

 data set. 



Second in importance was S. patens (23 percent) in the TUckerton marsh and L. 

 carolinianum (23 percent) and Salicornia spp. (20 percent) in the Great Bay Boulevard marsh. S. 

 patens was less common in the Great Bay Boulevard marsh but occurred at significantly higher 

 elevations as we expected: 122 cm (3.99 ft) versus 92.7 cm (3.04 ft) in the TUckerton marsh (Table 

 3-2). All of these species are indicative of high marsh or the transition above high marsh. While 

 much less common than in South Carolina, tall 5. alterniflora nevertheless is an important 

 indicator species of low marsh for New Jersey. We found that it occurred over 4 percent of the 

 composite transect but at higher elevations in the lower tidal range TUckerton marsh ( + 73 cm 

 [2.4 ft] than in the Great Bay Boulevard marsh (+48.5 cm [1.59 ft]). This apparent opposite 

 trend may be related to its occurrence along the banks of mosquito ditches and the possible 

 superelevated mean water levels within the TUckerton marsh. 



Phargmites communis (giant reed) was almost absent in the Great Bay Boulevard marsh but 

 was very common as a fringing species along the TUckerton marsh. Its modal elevation of 1.15 cm 

 (3.78 ft) provides a good indicator of the upper limit of yearly tides for the area, since it requires 

 fresh to brackish water. 



Figures 3-3 and 34 illustrate two hypothetical composite transects for the principal tidal 

 range areas around the TUckerton and Great Bay Boulevard marshes based on the results in | 

 Table 3-2. Each includes elevation divisions, species zonation, and representative tidal levels. The 

 profiles are by no means precise, but they provide an indication of the relationships between 

 each wetland subenvironment. 



70 



