23 



is this soil, and that the one agency most active m reproducing it, 

 and most valuable in restraining its waste, is the forest cover to the 

 land. 



If this were the only function of the forests it would be amplt 

 reason for throwing around them every protective care which was 

 not inconsistent with their legitimate uses for lumber and for fuel. 

 It is, however, but a part of what they accomplish. Not only do they 

 mechanically restrain the destructive force of the surface water, but 

 by that very act they give it a better chance to soak into and sat- 

 urate the adjacent earth. The downward pointing roots furthermore 

 serve as lines along which, with increased facility, the water pene- 

 trates to the depths beneath, where it is safe from immediate evap- 

 oration, and where it continues (possibly for months) to nourish the 

 smaller streams and to maintain the perpetual flow of our springs. 

 It is further to be observed that this water so saved is in immediate 

 proximity to the smallest rootlets, and is by them absorbed, taken 

 up through trunk and branches to the leaves, where it is evaporated 

 or transpired into the open air. In this flow upward from the earth 

 it not only carries the nutrient matters of the soil, to form the 

 fabric of the tree, but it returns in the form of vapor, to moderate 

 the temperature, a quantity of moisture which might well seem fab- 

 ulous. Thus it has been estimated by Dr. Evermayer that a beech 

 tree "fifty to sixty years old wo-uld transpire about twenty-two 

 pounds of water daily." Multiply this by four or five hundred trees 

 and that by the number of growing days in the year and the immense 

 volume of water Vhich an acre of forest land may furnish through the 

 leaves of the trees is at once apparent. Such an acre would restore 

 to the atmosphere during the six months, from April 1st to the last 

 days of September, about one thousand tons of water by evapora- 

 tion and transpiration from the leaves, and in the same basis a square 

 mile would furnish 640,000 tons of water, or reduce the number of 

 trees one half, and each square mile during the growing season 

 would return, to the air, over 300,000 tons of water. 



It has never been shown that this tremendous volume of water, 

 filtered o-ut from the earth to the clouds, through the trees, actually 

 increases rainfall over the region. But it does bring the atmosphere 

 there, by so much, nearer the point of saturation with moisture, and 

 just so much less water from other sources is needed to load the air 

 with moisture enough to cause a downpour of rain. 



There is, however, a relation of the utmost importance to the 

 humidity of the country, in which forests play a large part. It is 

 in preventing, directly and indirectly, the rapid evaporation of 

 moisture fromnot only thesurface which they cover, but from even the 

 surface of the streams themselves, as well as from the areas under 

 actual cultivation. Every pound of water resto-red by the trees to 



