16 THE UTILITY OF FORESTS. 



(c) Evaporation from the Soil. — Owing to the lower temperature, 

 the greater humidity of the air, and the quieter state of the 

 atmosphere, evaporation is considerably smaller in forests than 

 in the open. This has been conclusively proved by direct obser- 

 vations which have shown that it amounts to a reduction inside 

 forests of as much as 60 per cent, of the amount of evaporation on 

 open ground. In this respect the covering of the soil is of great 

 importance. Ebermayer's observations show that if : — 



Evaporation of water in the open is placed 



at ...... 100 parts. 



Evaporation from forest soil, without leaf 



mould is . . . . . 47 ,, 



Evaporation from forest soil with a full 



layer of leaf mould, is . . . 22 ,, 



In other words, forest soil covered with a good layer of humus 

 evaporates less than I of the water evaporated from soil in the open. 



(d) Summary. — The above data are general averages. The 

 actual figures for a special locality depend on a variety of condi- 

 tions such as species, the density of stocking, the temperature and 

 other climatic factors. On the whole, there can be no doubt that 

 forests preserve humidity to a considerable extent. On the other 

 hand, a forest crop consumes a considerable amount of water 

 through the action of the leaves. What that quantity is, has not 

 been definitely determined, nor how it compares with that 

 required by field crops. Ebermayer estimated that a well stocked 

 beech wood consumes a rainfall of as much as 14 inches. Coni- 

 ferous woods, especially those stocked with pines, require much 

 smaller quantities, while he estimated that required by a crop of 

 clover at 5 inches. In connection with these data it may be 

 mentioned that in India successful cultivation of forests is not 

 possible with a rainfall of less than 15 inches, even with little 

 exacting species. The consumption of water by forest crops 

 causes the soil in the region of the roots to be drier than below it. 



Attempts have been made to draw a balance between the water- 

 preserving and water-consuming capacity of forest crops. As far 

 as the available data permit any conclusion, it may be said that, 

 in the plains, forests probably consume more water than they 

 add to the rainfall, or even preserve by reducing evaporation. 

 With elevation in the hills, the reverse may be the case. Hence. 



