124 



PLANT SOCIOLOGY 



shrubby willows and alpine alders of the Rhodoreto-Vaccinion and the 

 fields of tall herbs, Adenostyles, Cicerhita alpina, Cirsium spinosisisimum, 

 etc. (Fig. 70). All the snowy mountains of the temperate zone have 

 such fields of tall herbs. 



Undergrowth and ground layers of forests receive very different 

 amounts of snow under different kinds of trees, since the crowns of the 

 trees catch and hold the snow in different degrees. According to 

 Biihler (1918), the spruce holds back 55 to 80 per cent of a snow in its 

 crown; the beech, only 10 to 15 per cent; a fifteen-year-old low forest 

 of Carpi nus, Conjlus, etc., only 3 per cent. Hence in low forest and 

 among shrubs we may expect the greatest influence of the snow upon 

 the ground layer. 



Fig. 70.— Cirsium spinosissivunn tall herb meadow in July, after melting of snow 

 (Val Sampuoir, 2,200 m.). f^Photo by Heller.) 



In the Pinus montana low forest of the calcareous mountains 

 between Inn and Etsch, several facies can be distinguished, dependent 

 on snow cover: 



1. The Pinetum montanae cladoniosum with an undergrowth of fruticose 

 Hchens (maximal snow cover 7 months) on northern slopes and in the depressions 

 known as snow pockets. Cladonia alpestris, C. rangiferina, C. siluatica, Cetrarin 

 islandica, with Vaccinium uliginosum mostly cover the ground. 



2. The Pinetum montanae hylocomiosum, with 2 to 4 weeks' shorter snow- 

 cover. The dominant plants are mostly Hylocomium splendent, H. triquetrum, 

 Hypnutn schreberi, with Vaccinium myrtillus. 



