FOREST POLICY OF THE INDIAN GOVERNMENT. 101 



importance. As far as forest vegetation assists in this, tlie 

 subject must be considered chiefly from two points of 

 view : — 



(1.) In respect of the evaporation of moisture. 



(2.) In respect of the mechanical action of forests. 



The difference in evaporation from an area exposed to the 

 full effects of the sun and anotlier sheltered by a dense growth 

 of forest vegetation must be much greater in a tropical country 

 like India, than it has been proved to be in a temperate 

 climate. Hence the presence of forests acts highly bene- 

 ficially wherever the rainfall is limited, or unfavourably dis- 

 tributed over the seasons of the year ; in other w^ords, 

 especially in the Indus and West-Gangetic plain and the drier 

 parts of the Peninsula and Upper Burma. 



There is, however, a second way in which forest vegetation 

 acts most favourably, namely as a help towards successful 

 irrigation. Of the 220,000,000 acres which are cultivated 

 annually in British India, no less than 30,000,000 acres are 

 artificially watered, either by canals, or from wells, lakes and 

 tanks. Some of the canals are fed with water derived from 

 the enormous snow fields of the Himalayas, and the rest with 

 water which comes from other sources. Accordingly, the 

 irrigated area may be classified as follows : — 



Area irrigated from canals . . 13,000,000 acres. 



„ wells . . . 10,000,000 „ 

 „ „ ,, other sources . 7,000,000 ,, 



Total . . . 30,000,000 „ 



Only some 5,000,000 acres, equal to 16 per cent, of the 

 total irrigated area, rely directly on the melted snow of the 

 Himalayas. Of the 10 million acres irrigated by well-water, 

 by far the greater part is situated in the Indo-Gangetic plain. 

 The wells in this plain may be said to tap great reservoirs 

 underlying the plain. Part of this water may come from 

 melted snow, but the greater portion consists, no doubt, of 

 the rain water which has sunk into the ground. 



