CH. VI 



INFLUENCE OF FORESTS 97 



has been proved by experiments carried out in Russia, 

 France, and India, where, under identical subsoil condi- 

 tions, both inside and outside forests, it was found that 

 the water-table inside the forest, although less liable to 

 fluctuations, was lower than in places outside. When 

 rain falls on a forest, the whole amount does not reach 

 the ground, but a portion is detained by the crowns 

 and trunks of the trees and re-evaporated into the air, 

 thus further increasing the latter's store of moisture. 

 If, then, a moist current strikes this cooler column it is 

 apt to become condensed and to give out rain, and 

 therefore there is every indication that forests increase 

 rainfall. 



Unfortunately, we have in the Tropics no absolutely 

 reliable data to prove this. In India Blanford 1 com- 

 pared the rainfall statistics over part of the Central 

 Provinces, which had been deforested by shifting culti- 

 vation and subsequently preserved, and found that there 

 was an increase of about 20 per cent in the rainfall in 

 about ten years. Experiments carried out in France in 

 the forest of La Haye, near Nancy, for thirty-three years 

 showed that the rainfall on the edge of the forest was 6*1 

 per cent smaller, and outside the forest 23*3 per cent 

 smaller, than in the centre of the forest. It was ascer- 

 tained that these proportions were independent of the 

 direction of the wind, and that the influence of the forest 

 is also independent of seasons. In Germany the rainfall 

 inside the forests is stated to be some 3 per cent heavier 

 than outside. 



There is, however, no doubt that much remains 

 to be done before satisfactory data can be obtained, 

 especially for the Tropics, where not only so much 

 depends on the monsoon currents, but also on the 

 character of the forests, which is of such a varied nature. 

 For example, it can be readily understood that the 

 dense equatorial forests give out a large amount of 

 moisture, which becomes frequently condensed and 

 returns in the form of rain ; but it is of more real 



1 See Indian Forester, vol. xxxvii. Nos. 3 and 4. 



H 



