5. Sources of Variability at Pine Knoll Shores . 



First inspection of the Pine Knoll Shores site suggested uniform 

 substrate, but the variable growth of the plantings indicated sharp 

 variations in substrate. Corings in April 1975 revealed no apparent 

 basis for this assumption. The substrate-related differences in 

 growth of Spartina altemiflora were confined to a few patches of 

 peaty remains of old marsh surfaces as shown in Figure 5. Trans- 

 planting on these was difficult and both survival and growth were 

 poor. 



The construction of elevated walks and docks in front of many of 

 the residences contributed to the high variability but was not the 

 major cause (Fig. 6) . 



The high variability in growth and in spread within these plantings 

 was probably caused by movement of the substrate surface. Minor 

 changes in the surface affect growth which, in turn affects loss and 

 accumulation of sediments. Cause and effect become so intertwined that 

 a clear separation is impossible. Where growth is above average there 

 is evidence of either accretion or sediment retention (Fig. 7] . This 

 makes comparison of small-scale plantings intermingled with unsuccess- 

 ful plantings difficult. 



The presence of the bulkhead close to the normal high tide line 

 aggravated this problem. Most of the plantings next to the bulkhead 

 were destroyed by wave action before winter (Fig. 8) . Erosion was 

 reduced where plants had survived and grown. 



6. Source of Plants . 



Previous work has shown definite differences in transplants taken 

 from different locations. Fourth-year data from an experiment at 

 Snow's Cut, North Carolina, are presented in Table 6. Differences 

 between sources are diminishing with time. Factors other than source, 

 i.e., elevation and competition from invading species, become important 

 as plantings mature. Also, how much one source has spread into another 

 is unsure. The results from this experiment confirm that transplants 

 from each of the five locations would be satisfactory on this site. 



A comparison of the results from an experiment at Pine Knoll Shores 

 involving transplants grown in an intertidal nursery at Beaufort from 

 two seed sources is shown in Table 7. Pine Knoll Shores has an eroding 

 shoreline, a more stressed situation than that at Snow's Cut. This 

 condition has magnified the difference between the local (Beaufort) 

 source (Fig. 9) and the foreign (Oregon Inlet) source (Fig. 10). At 

 the end of the first growing season, the Beaufort plants were distinct- 

 ly superior. Although both sources survived the winter, erosion was 

 more severe on the thinner, shorter stands of the Oregon Inlet plants. 



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