V. DISCUSSION 



1. Comparison of American Beachgrass Spacing Schemes . 



American beachgrass plots were planted to a standard width of 15 meters. 

 Plants In plot 1 were spaced 45 centimeters apart; plants In plots 3 and 5 

 were spaced 60 and 90 centimeters apart, respectively. In October 1977, the 

 lateral growth of vegetation was measured along each profile line. Table 8 

 summarized the observations made at each beachgrass plot. 



Table 8. Width of American beachgrass in 

 beachgrass plots, October 1977. 



Plot 



Description 



Profile 



Width 1 



No. 





line 



(m) 



1 



American beachgrass 



1 



71.3 





(45- by 45-centimeter 



2 



65.2 





spacing) 







3 



American beachgrass 



5 



48.5 





(60- by 60-centimeter 



6 



31.7 





spacing) 







5 



American beachgrass 



9 



89.9 





(90- by 90-centimeter 



10 



78.0 





spacing) 







^After seven growing seasons. 



Woodhouse, Seneca, and Broome (1976) report that in North Carolina, 

 American beachgrass spreads in the direction of sand supply at a rate of 2.4 

 to 3.0 meters per year. This spreading rate was exceeded in two of the three 

 beachgrass plots in the Nauset experiment. Vegetation in plots 1 and 5 ex- 

 tended laterally an average of 3.8 and 4.9 meters per year. Vegetation in 

 plot 3 spread more slowly. Plot 3, which has the foot and vehicular pathways, 

 was badly damaged in 1971 and 1972; survival of the initial and followup 

 plantings was only 10 to 20 percent. Initial survival in plots 1 and 5 was 

 high, 70 to 85 percent, which accounts for the greater spread observed in 

 these plots. Seaward spread of the vegetation in the three plots averaged 2.4 

 meters per year; landward spread was 4.8 meters per year. Winds are predomi- 

 nantly from the west during the growing season; therefore, vegetative spread 

 was greatest in the windward direction. This observation supports that of 

 Woodhouse, Seneca, and Broome (1976) concerning the rapid spread of American 

 beachgrass in the direction of sand supply. 



Table 9 summarizes the volume of sand accumulated under beachgrass and the 

 overall increase in crest elevation after seven growing seasons at each beach- 

 grass plot. The sand volume and the elevation increase in each plot are close- 

 ly related to the width of vegetation in each plot (Table 8). The greatest 

 lateral spread of vegetation and largest sand accumulation occurred in plot 5, 

 the plot with the greatest exposure to windblown sand. In addition to landward 

 and seaward beaches which contributed sand to all plots, plot 5 benefited by 



29 



