PART I. 



INFLUENCE OF FORESTS ON WATER SUPPLIES. 

 Although this is a subject of great importance to this country, and 

 one much discussed of late, it has never been carefully studied. Even 

 European foresters, who have investigated this subject for many years, 

 have not as yet established their final conclusions covering the whole 

 field. That a relation does exist is indisputable, for forest destruction 

 always produces a change in the character of the stream flow. 



INFLUENCE OF FORESTS ON RAINFALL. 



Rainfall is caused by the cooling of moisture-laden air to below the 

 dew point. Forests shade the ground, making it cooler and conse- 

 quently keeping the air above it at a lower temperature than that of 

 the surrounding air. It is reasonable to suppose that rain might fall 

 over a forested area when it would not if that area were cleared. On 

 the western prairies this is a popular conviction, but observations 

 made in Europe have yielded conflicting results, and no definite con- 

 clusion can be drawn from them. 



INFLUENCE UPON THE DISPOSAL OF RAINFALL. 



, It is after the rain has reached the earth that the forest exerts its 

 most potent influence. Rainfall escapes in four ways from the ground 

 upon which it falls : by evaporation, transpiration, surface run-off and 

 seepage run-off. 



Evaporation. 



The rapidity with which moisture evaporates depends on its ex- 

 posure to the sun and wind. A thick forest cover shades the ground 

 from the direct rays of the sun, thus preventing too rapid evaporation. 

 Experiment has shown that from the surface of a small pond, situated 

 in the open, three to four times as much evaporation took place as 

 from a similar sheet of water in the forest. Experiments made on 

 the surface soil in California gave practically the same results. From 

 1,000 square centimeters of bare ground 5,730 grams of water were 



