BIOTIC FACTORS 



275 



earth various degenerative stages appear, leading away from the 

 dimax. In the Mediterranean and north African countries character- 

 istic degenerative phases of vegetation due to overgrazing include com- 

 munities dominated by thistles and by such species as Zizyphyus 

 lotus, Ferula communis, Peganum harmala, Euphorbia characias, E. 

 nicaeensis. In southern France, with moderate overpasturing, upon 



Fig. 141. — Effect of cattle grazing on Fagus. The Nardetum is conditioned and 

 maintained by moderate grazing; in the beech climax of the Cantal mountains 1,200 m., 

 Auvergne. {Photo by Uehlinger and Riibel.) 



compact limestone soil and red soil, the Brachypodium ramosum- 

 Phlomis lychnitis association takes possession. In the mountains of 

 central and southern Europe and in northern Europe, meadow com- 

 munities with abundance of Nardus have become very widespread 

 under the influence of severe pasturing (Fig. 141). A characteristic of 

 heavily grazed land of central, western, and southern Europe is the 

 prevalence of Juniperus bushes. Juniperus communis and, in the 



