48 



PARAGRAPH XIX. 



EVAPORATION OF SOIL MOISTURE. 



There is a vast difference betxx^een the evaporation from field 

 soil and from forest soil, especially if the leaf litter is left on the 

 ground in the forest. 



In the latter case, after Ebermeyer, the evaporation from forest 

 soil is only 16 per cent of the evaporation from field soil. When 

 the litter is removed by rake or fire, the proportion is 38 percent. 



On the other hand, the evaporation from the crowns of the 

 trees is enormous. The forests irrigate the atmosphere. Forests, 

 it may be said, are the greatest consumers of water on earth. 

 Observations in the Russian steppes prove conclusively that the 

 level of the groundwater is lower beneath the forests than in 

 the country surrounding them. Where there is water, we in- 

 variably find forests. Cause and effect should not be mixed. 



Evaporation largely depends on the velocity of the wind. The 

 velocity being reduced by sheltering belts of forest, drought might 

 be checked locally by screens of woodland placed, gridiron- 

 fashion, across country at proper intervals. (Compare Green, 

 p. 28.) 



