THE FOREST IN RELATION TO MAN 379 



that strikes the mulch ^ soaks through slowly ; then, in the en- 

 tangled soil beneath, it steadily works down to form the under- 

 ground streams and the springs. Snow in the forest melts 

 slowly and is gradually absorbed in the spongy bed beneath ; 

 from this the water slowly escapes into the springs and under- 

 ground currents. Snow upon the bare ground runs off as fast 

 as it melts. 



Actual proof of the difference was furnished a few years ago by 

 an extensive experiment conducted by the United States Geological 

 Survey in the White Mountains. Two similar areas were selected, 

 each covering about five square miles. One of the regions had been 

 entirely cut down and burned over; the other retained the virgin 

 forest (Fig. 197). 



The practical bearing of these facts is not hard to under- 

 stand. Every year, as the snows on the hills begin to melt, 

 the water rushes down the hillsides in the deforested regions, 

 causing the streams to overflow their banks and the torrents 

 to tear down and destroy everything in their path. The 

 annual damage done by floods in this country is estimated 

 to be equal to one hundred million dollars. This does not 

 include the destruction of human life that is often involved 

 in the floods. 



Streams depending upon deforested areas for their water will 

 be too full in the spring and will run too low in the summer. 

 Water used for agricultural purposes must be had in abun- 

 dance throughout the summer, and the destruction of forests 

 in one region has often resulted in the ruin of agriculture 

 and the migration of peoples in a distant valley. Navigation 

 on the larger streams is influenced by the forest in two ways : 

 the steady flow of water is maintained by a proper condition 

 of the forest, and the filling up of the stream by soil is at the 

 same time prevented. 



1 The mulch forms a soft, absorbent carpet, consisting largely of decaying 

 leaves and other organic matter. _ 



