Forest Influences 305 



unusually heavy and long-continued rain is necessary to 

 cause a flood in a stream whose water-shed is well forested. 

 This water that soaks into the ground gradually seeps 

 to lower levels and finally emerges from the springs to 

 maintain the normal stream flow. Naturally a moderate 

 rise in the streams occurs after a prolonged period of 

 heavy rainfall, but such a rise can do little or no damage, 

 and, as we have seen, a sudden and destructive flood is 

 impossible. 



The snow is disposed of by the forest in the same way 

 as the rain. The crown cover shuts out the rays of the 

 sun and prevents the snow from coming under the heat of 

 direct insolation. It is late in the season in the mountain 

 regions when the temperature in the shade rises sufficiently 

 to melt the snow for any length of time during the day. 

 Thus the run-off from the forested mountains is practically 

 none when the snow is melting rapidly in the early spring 

 in the open and in the lowlands. The water supply from 

 this region is kept stored up in the ground and in springs 

 as a reserve that keeps the streams flowing through the 

 dry months when other sources are exhausted. Observa- 

 tion of two streams in California, one with a bare water- 

 shed and the other with water-shed well forested, has 

 proved this almost conclusively. The streams were 

 well located in a region in which there was a distinct rainy 

 season followed by absolute drought. The bare water- 

 shed sent down its waters immediately after the rain in 

 torrential floods carrying away everything movable 

 along the banks and making any use of the water impos- 

 sible. Shortly after the close of the rainy season, the 

 volume of the - stream began to decrease rapidly and in two 



