78 PLANTING OF SAND DUNES. 



a time, and the operation is continued.' The dune under this manage- 

 ment rises highei*by degrees and assumes a slope of from 7 to 12 degrees 

 in front, and much less on the land side. Practically, the angle of ele- 

 vation is best at about 7° above the horizontal in front and 22° in the 

 rear. The wind passing over the barrier strikes down upon the opposite 

 side, and, hollowing out the sand somewhat, passes off, with its force 

 practically broken. The front slope may be concave in some degree. 

 As soon as the palingis set, they begin to plant tufts of Arundoarenaria in 

 front, and in a belt eight times wider than the obstacle oi)posed. These 

 tufts are in quincunx order, and closer together near the paling. The out- 

 side of these stop some of the sand, those farther up stop more, and thus 

 an even slope of the desired angle is secured and maintained. This plant 

 is set in winter, and they sow between them the seeds of the same and 

 of Triticum pmccum, Artemisia, Kalcile maritima, Salsola, Ephedra, and 

 other maritime plants. Sometimes brush are set in the sand, which 

 answers a good purpose. When the dune has raised some 12 meters in 

 height, it may be widened at the top by substituting for the planks a 

 quadrui)le row of brush in quincunx, some 15 inches apart. A dune 12 

 meters high contains 720 cubic meters of sand to each meter, running 

 measure, and, where the sand comes in at the rate of 25 cubic meters a year, 

 would be 30yearsin forming. The increase is then about 12 inches ayear, 

 a rate of growth which the tamarisk will support, and this shrub may 

 then be planted on the top. The slope should not be raised more than 

 12° in front, and it is sometimes necessary to carry the paling farther 

 back, by setting a new line, the top being first widened by means already 

 mentioned. 



Stability and steepness are sometimes secured on the land side by a 

 fence of stakes and woven brush, which must be renewed by adding to 

 the top from time to time. The greatest protection is afforded when the 

 lee side is as steep as the sand will lie. The grass and other plants 

 planted on the front slope grow upward as they are buried, and thus 

 the sand is bound together in a firm net work of fibers. A hectare re- 

 quires 300 bundles of this plant, weighing about 22 pounds each, besides 

 13 pounds of seeds.2 These seeds are sown broadcast, and no covering 

 is required other than comes from treading into the sand as the work- 

 men pass to and fro. A meter of paling costs 2.5 to 3.0 francs (16 to 25 

 cents per foot), and will last (if made of sap-wood of the maritime pine, 

 and not injected) about five years. Their maintenance costs half a franc 

 a year, and the fencing with stakes and brush costs a third of a franc 

 yearly. 



In storms the wind will sometimes make breaches in the littoral dune, 

 which must be repaired by new palings in lines oblique to the main di- 

 rection, on the steep side, until the sand piles up to fill them. Au irrup- 



1 A rude and expensive way of raising, first tried, was by digging away the sand till 

 the boards could be raised by band, when they were planted anew. This softened the 

 sand and made it liable to be scooped out by eddies of wind. They next tried a lever, 

 placing a chiiiu around the plank to be raised and using the top of the next adjoining 

 one as a fulcrum. By raising a little at a time and getting a new hold they could 

 thus slowly raise them to the desired height. By carrying movaMe supports along and 

 raising by levers on opposite sides, using four to eight men for the service, the same 

 could be effected. A movable windlass slid along on the sands was au improvement, 

 because the traction was vertical; but finally a movable frame with a long lever 

 mounted on runners that could be slid along the fence to be raised, with pincers and 

 chain, was found to operate with the best advantage. The chain passed over au arc 

 of a circle, near the head of the lever, and thus drew vertically. It is easily carried, 

 and may be worked by one man. 



^2 Equal to 121 bundles of the plant and 5.2 pounds of seed to the acre. 



