CLIMATIC FACTORS 



153 



Wandering Dunes. — The stabilization of truly wandering dunes by 

 natural plant communities is well-nigh impossible without human aid, 

 even where the wandering dunes are separated by wide interspaces. 

 Nevertheless, the behavior of natural plant communities gives most 

 helpful suggestions for the artificial control of the dunes (Fig. 162). 



In the great region of wandering dunes between Cape Sim and Cape 

 Ghir, on the south Moroccan coast, there lies between the dunes which 

 are 20 m. or more in height an extremely characteristic succession of 



Fig. 90. — Aestival aspect of the Ammophila-Mcdicago marina association at Carnon, 

 near Montpellier (in the foreground Echinophora spinosa and Euphorbia paraUas). 

 {Photo bij Riibel and Uehlinger.) 



communities. The study of this succession has led to rational methods 

 of dune control. It begins on the strips of land most recently left by 

 the dunes. The initial stage is made up of Ononis tournefortiana and is 

 followed by a closely crowded association of 0. angustissima. This 

 is later overgrown by a scrub of Rctama ivebbii, but before the last is 

 fully developed the next dune rolls in and buries the scrub. 



Artificial stabilization of dunes begins with the 0. angustissima 

 stage, which is planted by the hectare. Seed-bearing shoots are 

 scattered about over the area and anchored with sand. When the 

 Ononidetum has taken hold, Retama is sowed in it, or it appears sooner 

 or later naturally and without any help (Fig. 163). 



