CLIMATIC FACTORS 



121 



munities on snow ground, favored by the protective covering of snow. 

 The snow-avoiding communities are also always wind hardy. Between 

 these fundamental ecological groups there are associations more or less 

 favored by snow, such as the Cur- 

 vuletum and the Festucetum halleri. 

 In the calcareous Alps the follow- 

 ing associations occur on closely 

 adjacent surfaces: Elynetum on ex- 

 posed slopes often swept bare of 

 snow during the winter; Seslerieto- 

 Semperviretum a httle lower down 

 on slopes covered during the winter, 

 but from which the snow disappears 

 early; Festuca violacea-Trifolium 

 </iaZw association in depressions where 

 the snow lies late but where the 

 water supply is good; and Arabidetum 

 coeruleae on areas where the snow 

 lies very late. 



Snow-land Communities. — Snow- 

 land communities are adjusted to a 

 very short growing season. They 

 tolerate 8 to 11 months spent in 

 hibernation. Indeed, there are 

 facies of the Polytrichum sexangulare 

 association which in snowy years are 

 never exposed (Figs. 67, 68). 



In the high mountains of northern 

 Scandinavia, according to Fries, the 

 Phippsia algida and the Anthelia 

 nivalis associations are denizens of 

 extreme snow-land. The Ranuncu- 

 lus glacialis and R. nivalis meadows 

 as well as the Salix herhacea asso- 

 ciation with its abundant liver- 

 worts and mosses endure a very 

 long continued snow cover. The 

 snow-land communities of the 

 Alps and the Tatra mountains fall 

 into three floristically different alliances: 



The Arabidion coeruleae; on calcareous snow-land, a pronouncedly basophilous 

 community. 



= Polyfrichefum sexangular'is 

 Snow cover 8'/z '9'/2 months 



= Sa/icefum herbaceae 

 Snow cover 8-9 monihs 



-■ Griaphalium supinum 



Snow cover 8-9 monihs 



= Curvulefum 



Snow cover 7-6 monihs 



= Loiseleun'efum cefrariosum 

 Always wiihoui snow 



Fig. 67. — Topographic arrangement 

 of some associations with various dura- 

 tion of snow cover in the Farur Alps, 

 2,350 m. {Braun-Blanquct and Jenny.) 



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