128 FORESTS AND MANKIND 



allows it to come again to the surface in the form of springs 

 and steadily running streams. Of course, if the storm is heavy 

 and of long duration, not all of the water is absorbed. As the 

 soil becomes saturated, the rain no longer sinks in it runs 

 over the earth's surface and down the stream beds. But there 

 is no sudden destructive rush no carrying away of great quan- 

 tities of fertile soil, and no silting up of reservoirs. And al- 

 though the forest cover can not, of itself, prevent floods, it is 

 an important factor in decreasing their severity, especially on 

 heavy clay soils. In Europe foresters and engineers have learned 

 that one of the most important steps in controlling floods is to 

 reforest the steep banks of their streams. 



In winter the snows that fall beneath the shade of our for- 

 ested mountainside remain unmelted much longer than snow 

 exposed to the direct heat of the sun. So when spring comes and 

 the sun's rays become hotter, the snow in the open spaces 

 shrinks rapidly and the water goes off quickly. So for the rest 

 of the summer, unless there are heavy rains, the streams are 

 dry. But under the leafy protection of the forest, snowbanks 

 melt much more slowly and even in July or August are giving 

 off their precious moisture to the agricultural land beneath 

 them. As a result, the streams on which whole communities 

 may depend are fed by the forest snows until later summer and 

 the droughts that occur in the open country are often avoided. 

 This water, so valuable in regions that depend wholly on 

 irrigation for their farm crops is one of the things made possible 

 by the forest shade. 



The streams that supply drinking water for cities must above 

 all be kept clean and pure, and to this end our forests play the 

 great role of guardian of our health. For the forest streams are 



