HOW THE FORESTS HELP MANKIND 127 



mountain sides. They are both exactly alike, except that one 

 is covered with forest, and the other is bare. Over both areas 

 bursts a heavy storm. On the treeless slope with its surface 

 baked by the sun's rays, the rainfall pours down, but does not 

 sink into the soil. Instead it runs over the surface of the earth 

 with increasing swiftness and rushing down the stream beds in 

 a wild torrent, carries along great quantities of the most fertile 

 soil and with the force of its headlong course carves out deep 

 channels over the countryside. If these streams flow into reser- 

 voirs, as in the West, all this fertile earth washed away by the 

 storm is not only lost but actually becomes a menace to agri- 

 culture. For after each heavy rain tons on tons of earth are 

 deposited in reservoirs that many localities depend on for 

 irrigation and only at great expense and effort can these reser- 

 voirs be kept from filling with silt. If the rain is sudden and 

 severe, these muddy rivulets may combine to form a raging 

 torrent, rushing wildly down the mountain and perhaps wash- 

 ing out roads and destroying bridges. So under these conditions 

 the rainfall has not served the country in any beneficial way. 

 On the other hand, it has brought damage to bridges, reser- 

 voirs, roads and to the soil itself. 



Something quite different is happening over on our forest- 

 covered mountain side. In the first place the force of the rain 

 has been broken by the branches and leaves and the raindrops 

 fall gently to the ground or run down the tree trunks. Part 

 of the rain, too, is absorbed by the leaves and in light summer 

 showers very often no water reaches the ground it is all ab- 

 sorbed. But the rain that finally falls upon the soil finds a 

 soft cover of leaves and loose earth which like a great sponge 

 absorbs most of the water and later, days later sometimes, 



