96 



water level of the streams. But his rejiort has been shown to be so fnl: 

 of glarluii iiiacourafie;- and misstatements that its conclusions are almost 

 wholly discredited by scientific men. (12), (29), and (3S.) 



Other literature, much of which has contributed nothing new to the 

 subject, has been gone over and after considering all the facts it may be 

 safely said that the weight of evidence seems to show that forests do in- 

 crease precipitation, at least to a small extent. 



Evaporation. 

 Under the best of conditions much of the precipitated water is lost 

 by evaporation. The proportion evaporated varies gi'eatly in different parts 

 of the world and under different conditions of season and soil. It de- 

 pends principally on the temperature, the wind, and the amount of moist- 

 ure alre:idy in the air. That the forest retards evaporation cannot be 

 denied. The shade which it affords the s<^)il and its relatively cooler tem- 

 perature in sununer retards evaporation to a great extent. The greater 

 amount of moisture in the atnios]>here of the forest is another factor which 

 reduces evaporation. Winds are checlved by the forest and their iKJwer 

 to take up moisture limited. The wind and sun in winter evaporate a 

 great portion of the snowfall. In the San Rernardiuo Muinitains, snow- 

 falls a foot in dejitli are fre(iuently evaiw)rate<l in two or three days with- 

 out even moistening tlie soil. The forest aids in reilucing this loss in so 

 far that it furnishes shade and checks the wind. K.xperinients in Ger 

 many have jimved that evaporation luider trees is altout one-half of that 

 In the open and show a sjiving of 21 per cent, of the precipitation by the 

 wood.s. The evaiKpration and saving by the forest were both greatest i'l 

 M;iy and June. It was also found that deciduous trees when in leaf re- 

 tarded evaporation more than the evergreens and that evaporation under 

 young trees was only 20 per cent, less than in the open. Following is 

 data from a series of investigations by Dr. Eberniayer and by Cierman in- 

 vestigators : 



