RELATIONS OF TREES TO WATER 299 



upon the hills, to be retained by the mechanical 

 action of the trees and their undergrowth of shrubs 

 and herbaceous plants, and by the spongy surface 

 of the soil underneath them, made porous by mosses, 

 decayed leaves, and other debris, so that the plains 

 and valleys have a moderate oozing supply of mois- 

 ture for a long time after every shower. Without 

 this covering, the water when precipitated upon the 

 slopes, would immediately rush down over an unpro- 

 tected surface in torrents upon the space below. 



Every one has witnessed the effects of clearing the 

 woods and other vegetation from moderate declivities 

 in his own neighborhood. He has observed how 

 rapidly a valley is inundated by heavy showers, if the 

 rising grounds that form its basin are bare of trees 

 and planted with the farmer's crops. Even grass 

 alone serves to check the rapidity with which the 

 water finds its way to the bottom of the slope. Let 

 it be covered with bushes and vines, and the water 

 flows with a speed still more diminished. Let this 

 shrubbery grow into a forest, and the valley would 

 never be inundated except by a long-continued and 

 flooding rain. Woods and their undergrowth are 

 indeed the only barriers against frequent and sudden 

 inundations, and the only means in the economy 

 of nature for preserving an equal fulness of streams 

 during all seasons of the year. 



At first thought, it may seem strange that the 

 clearing of forests should be equally the cause both 



