CLIMATIC FACTORS 



155 



sharply marked, because the wind also conlrols the distribution of the 

 snow. The vegetation of habitats exposed to wind is totally different 

 from that of protected places, so that even in still weather the wind 

 relations of the habitat can be deduced from the vegetation. These 

 relations have been minutely studied in Lapland and in the Swiss 

 Alps. In Lapland the characteristic associations of wind-swept places 

 are tiie Parmelia lanata, Gyrophora prohoscidea, Hierochloe alpina, Dry as 

 octopelala, Diapensia lapponica, and the Loiseleuria procumbens 



Prevailing 



26Wm. 



— _— OoO. . , 



high wind 



C - \ 







•"Oo 



» V"'^ 

 'h:^ 



.««^ 



*Y, 



Curvulefum 



Elyneium 

 WSx;\ Ligusficum mufellina 

 l^^~l Sesterion coeruleae 

 I.'-.'.! Gravel slide 



Fig. 91. — Alternation between the Elynetum and the Curvulatum at the Murterjoch 

 Swiss Alps, 2,600 m. {Braun-Blanquet and Jenny.) 



association with abundant Hchens (Fries, 1913). In the Central Alps 

 the Loiseleurietum cetrariosum covers wind-swept crests and hogbacks. 

 This acidophilus azalea heath with abundant lichens presents several 

 variants, which differ in their resistance to wind.^ On thin calcareous 

 soils this association is replaced by the Caricetum firmae, with abun- 

 dant Dryas. At the higher mountain levels, the extreme habitats, 

 blown bare of snow all winter, are occupied by the Elynetum, the 

 Curvuletum elynetosum, and the Curvuletum cetrarietosum with 

 abundant mixture of wind lichens {Thamnolia vermicularis, Cetraria 

 cucullata, C. nivalis, C. juniperina). 



1 The most resistant dwarf -shrub community of the greater Alps is the Loiseleu- 

 rietum alectorietosum, a sub-association of the Loiseleurietum cetrariosum with 

 Aledorin ochroleuca, A. nigrescenfi, etc. 



