series of fences. In a Michigan project (Lehotsky, 1941), 2. 5- centimeter- 

 diameter wooden stakes were driven 5 centimeters apart into the sand leav- 

 ing 30 centimeters protruding above the surface. The stakes formed 4-meter 

 squares. On critical slopes, they were reinforced by a row of pickets 

 placed diagonally across the center of each square. This arrangement 

 effectively resisted winds of 105 kilometers per hour from the southeast 

 on 1 day and 92 kilometers per hour from the southwest the next. Similar 

 designs formed with stems of the common reed (phragmites) are used on the 

 Dutch coast. 



A square-to-rectangular pattern tried on a limited scale on large 

 dunes in northern Florida consisted of a 60-centimeter slat fence (stand- 

 ard 1.2-meter fence, cut in half) arranged in squares 3 to 5 meters on a 

 side. This approach uses half of the fencing, about two-thirds the amount 

 of posts, and much less labor compared with a similar design using 1.2- 

 meter fence. It requires less labor than driving individual pickets into 

 the sand. It should be just as effective if a high enough proportion of 

 the bare area is included. The 60-centimeter height is preferred with 

 planting as it limits sand accumulation to a depth more likely to be 

 tolerated by the developing vegetation. 



It is generally necessary to treat a large proportion of the area 

 (80 to 90 percent) for full control with any of the above methods. 



4. Vegetation . 



Vegetation is the only long-term stabilizer suitable for general use 

 on sand dunes. It is the only stabilization with self-healing capability 

 and the ability to grow and change with the dune. Plant selections, 

 planting procedures, and maintenance for vegetative stabilization of 

 bare sand in the barrier dune zone are the same as for dune building 

 in the same region. The difference is in plant spacing and planting 

 pattern. 



A uniform planting pattern is usually appropriate for stabilizing 

 the sand mass in place. 



Spacing requirements vary with plant species and site exposure. 

 In general, American beachgrass, bitter panicum, and sea oats should 

 be spaced 60 by 60 centimeters on center, and European beachgrass, 45 

 by 45 centimeters on center. Plant spacing should be less on exposed 

 sites such as dune crests--30 centimeters apart for European beachgrass, 

 45 centimeters apart for the others. Planting should begin on the sand 

 source side near the windward edge of the site and extend over the entire 

 sand mass. Partial planting is seldom effective because scouring of the 

 unplanted surfaces usually undermines the planted strips or blocks, ulti- 

 mately requiring the whole job to be done over. 



Establishment of vegetative cover on large areas of mobile sand is 

 difficult, particularly under high-energy conditions. Success is not 

 always possible on the first attempt, and it may be necessary to supplement 



102 



