PROTECTION AGAINST FIRES AND MOVING SAND 35 



by the wind. Occasionally it is necessary to cover the walls 

 with layers of palms to hold the dry sand in place. According 

 to an official inspection report it is necessary either to peri- 

 odically raise the outside defense hedge, to accumulate as great 

 an amount of sand as possible and thus form a thoroughly stable 

 dune which serves also as a permanent windbreak; or else to 

 build a cordon of brush at the foot of this dune, in the process 

 of formation, in order to make the sand pile up into a rather 

 low plateau which would serve as a base for a great protective 

 dune. In other words, the wind itself is harnessed to pile up 

 a sufficient mass of sand, as a barrier to prevent drifting, by 

 first building a sand wall at right angles to the wind, topped 

 with a palm leaf hedge which holds the particles of sand; then, 

 when this is buried, the operation is repeated and the dune 

 raised to the necessary height. 



Sand Drifting from Local Overgrazing. — Where the soil 

 immediately bordering an oasis has been disintegrated by over- 

 grazing the resulting damage can be readily overcome by form- 

 ing a protective zone closed to stock. This area is fenced with 

 sand walls similar to those described above, occasionally sup- 

 plemented by barbed wire. When protected, the soil, dry as it 

 is, quickly reseeds; the resulting sod will prevent all drifting. 

 After the movement of sand has been stopped, there often 

 appear the following spring some of the native grasses such as 

 Retama raetam, Aristida pugens, Limoniastrum guyonianum, 

 Atriplex halimus, Nitraria tridentata, peganum Harmale, 

 Zygophyllum album, Calligonum comosum, together with 

 Euphorbia guyoniana and Euphorbia blasamifera. These 

 grasses which are native of the desert, particularly Aristida 

 pugens, are often artificially sown as soon as the movement of 

 sand has stopped. 



The shrubs which are being used for reclaiming the mo\dng 

 sand areas in the deserts are Tamarix africana and Tamarix 

 articulata. At first it was thought that Tamarix africana, 

 being of local origin, would grow particularly well. The practice 

 of several years, however, has shown that winds often injure its 

 young shoots and the summer heat dries out the soil to a depth 



