MECHANICAL ACTION OF FORESTS. 139 



moderately high hills and low lands. The larger the proportion 

 of the catchment areas, whence this irrigation water comes, is 

 shaded by forest growth, the more sustained will be the supply of 

 water. Here then is a mission which forestry in India has to fulfil. 



4. Mechanical Action of Forests. 



The mechanical action of forest vegetation on sloping ground 

 is not without importance in India. There is sufficient evidence 

 to show what careless or injudicious clearing of forest may do. 

 Anyone who has ever stood on the hills behind Hushiarpur in the 

 Punjab and looked down upon the plain stretching out towards 

 the south-west, has carried away an impression which he is not 

 likely to forget. In that part the Siwahk range consists of an 

 exceedingly friable rock. Formerly the range was covered with 

 a growth of forest vegetation, but some time ago cattle owners 

 settled in it, and under the combined attack of men, buffaloes, 

 cows, sheep and goats, the natural growth disappeared, while the 

 tread of the heavy beasts loosened the soil. The annual monsoon 

 rains, though not heavy, commenced a process of erosion and of 

 carrying away the surface soil. Gradually ravines and torrents 

 were formed which have torn the hill range into the most fantastic 

 shapes, while the debris has been carried into the plain, forming 

 fan-shaped accumulations of sand reaching for miles into the 

 plain, covering and rendering sterile extensive areas of formerly 

 fertile fields. The evil will grow in extent unless curative 

 measures are taken. Means of checking the mischief were con- 

 sidered for many years, and by 1896 the destruction had extended 

 over an area of about 150 square miles. Grazing and wood 

 cutting were then limited, and in 1913 steps were taken to deal 

 systematically with afforestation in the affected areas. [See 

 page 140.] 



Although the case of the Hushiarpur Chos, as they are called, 

 is the worst of its kind in India, there are other instances which 

 prove that afforestation is essential on hill sides, wherever the 

 rock is friable and likely to be dissolved and carried away by the 

 continued action of water. It would, however, be a mistake to 

 assume that every hillside requires to be under forest. This is 

 not the case, wherever the rock is firm and capable of holding its 

 own without the steadying help of a growth of forest vegetation. 



