236 THE ALPINE THICKETS AND FORESTS 



the Pine forests is in relation to the altitude of the 

 floors of the Alpine valleys on the one hand, and the 

 snow-line on the other. The upper limit of the 

 forests, which is as a rule very sharply defined, 

 bears a definite relation to both. In the case of 

 a wooded Alpine valley, the following sequence can 

 generally be determined : — 



Immediately above the valley 

 Pe^etual Aoo^ and the Alpine meadows 



Snow. the forests rise, clothing the 



ZT valley -sides for 1,000 or 



Pasfures. 1,500 feet. The gap between 



the upper frontiers of the 

 Forests. forest and the snow-Hne is 



^ Alpine Meadows, ^^^^d by the treeless higher 



Valley floor. pastures, extending upwards 



for some 2,000 to 2,600 feet. 

 It has already been explained (p. 170) that the height 

 of the snow-line varies in different parts of the Alps. 

 The upper limit of the forests, for the most part, varies 

 in height according to the position of the snow-line 

 in that particular district, and keeps at a respectful 

 distance of 2,000 feet or more from it. 



Further, just as the mean level of the floors of the 

 Alpine valleys varies in elevation, so the vertical dis- 

 tribution of the Larches and Spruces which clothe their 

 sides changes. Probably exposure to wind is one of 

 the great factors that determines the upward limit of 

 the forests. So long as they are in some measure pro- 

 tected by the "brow of the hill," the trees can flourish. 



