CLIMATE AND WATER RELATIONS 



157 



Fig. 3. Average wind velocity at several locations on the eastern and western slope 

 of the Gurgler vaUey. Cross-section of the Gurgler valley. The points indicate the 

 places where measurements were taken. (From Aulitzky, 1958.) 



loss of the vegetation in summer because the effect of the wind on transpira- 

 tion is only great at a very low velocity. It decreases rapidly with increasing 

 wind velocity (Stalfelt, 1932). 



To summarise, during the summer at an altitude of 2000 m plants may 

 not be subjected to much stronger evaporation than plants in lower regions. 

 The lower water content of the air is more than compensated by lower air 

 temperatures above which plants may be heated only a little more than 

 those of lower regions. 



This is confirmed by measurements of evaporation at several places of 

 the station area (Prutzer, 1961) if we compare them with those values which 

 Walter (195 1) has collected from different chmatic regions. In late summer 

 evaporation (measured with the Piche Evaporimeter) rose only a little over 

 I ccm/h in our location in 2000 m. It is therefore not higher than in lower 

 regions of Central Europe. 



If the other conditions are the same, water absorption of plants depends 

 on the water storage in the soil which in turn depends on the amount of 

 precipitation. 



Precipitation increases rapidly with increasing altitude (Turner, 1961b). 

 This is especially true for the peripheral zones of the Alps (Fig. 4). Our 

 research area, however, is sheltered from the wind bringing precipitation 

 by mountain chains. Therefore it receives comparatively little precipita- 

 tion; only 1000 mm/annum on the average. The maximum amount of 

 precipitation falls in summer from July to August. The minimum occurs 

 in March, i.e. before the growing season (Table i). 



