plantings with fences, nets, or other devices. However, closer spacing 

 of plants and attention to the important details of plant quality and 

 planting procedure will generally be the most economical and satisfactory 

 method. 



Fertilization may be more critical to the success of planting for 

 stabilization than for dune building. The sand to be planted may be 

 more highly leached of its nutrients and it is not likely that fresh 

 sand will be entering the planting. If this is the case, fertilizer 

 is essential to the establishment of vegetative cover, and periodic 

 applications may be required for maintenance. 



5. Stability . 



The stability of fence-built dunes is usually short-lived without 

 continued maintenance. Deterioration of the fences will start the re- 

 lease of sand within 1 to 3 years. This usually results in the eventual 

 disintegration of the dune unless natural revegetation has stabilized 

 it. The extent to which natural revegetation of fence-built dunes occurs 

 varies widely. Revegetation usually begins on the back slope and crest, 

 and is slow to cover the front of the dune. More often, fence-built 

 dunes disappear after some years leaving, at most, a few vegetated dune- 

 lets located around some of the remaining posts (Woodhouse, Seneca, and 

 Broome, 1976). Consequently, fence-built dunes should be planted early 

 in their development. 



Unvegetated, fence-built dunes offer little resistance to storm surge 

 and wave action, and are easily eroded when overtopped. 



Vegetated dunes are stable against wind as long as their cover is 

 intact. Sand movement out of a good vegetative canopy is insignificant 

 even under extremely high winds. Stable foredunes such as those on North 

 Padre Island are periodically subject to hurricanes. The foredunes on 

 the Clatsop Plains of Oregon were planted in the 1930 's and continue to 

 grow, withstanding the strong winds for over 40 years. 



Vegetated dunes are moderately resistant to storm surges and waves. 

 They cannot withstand undermining by persistent beach recession, but 

 well-vegetated dunes are surprisingly tolerant to short-term wave attack 

 and brief periods of overtopping by storm surges. This was evident on 

 Ocracoke Island following Hurricane Ginger in October 1971 (Woodhouse, 

 Seneca, and Broome, 1976). Substantial amounts of water flowed over the 

 experimental dune during the storm and began serious undermining at the 

 rear without breaking through the cover on the crest or upper three- 

 fourths of the seaward slope. Instead, the grass cover caught sand on 

 the crest and seaward slope (Figs. 33 and 34). Wave action created a 

 low scarp on the seaward edge of the dune, but wind action filled this 

 within 48 hours Within less than a week new shoots of the dune grasses 

 emerged and the self-healing process was in operation. 



103 



