200 EFFECTS OF FORESTS ON SPRINGS AND RIVERS. 



After reporting their opinion in regard to the effects of forests on 

 the distribution of the rainfall, the Commissioners go on to say : — 

 " The copious flow of springs, and the abundance of water in riTers, 

 however, does not naturally depend' solely on the quantity of rain 

 falling in the course of the year ; for, on the one hand, a very con- 

 siderable quantity of the rainfall is returned by evaporation to the 

 atmosphere ; on the other hand, the nature of the soil determines, in 

 a great measure, the quantity of the rainfall which sinks into it, 

 forming subterranean reservoirs from which springs are fed. 



''In regard to both of these phenomena, forests exercise an influence 

 which can hardly be estimated too highly. 



" It is proved by direct observation in France, and in the forest 

 stations for meteorological observations in Bavaria, that the variations 

 in the temperature of the air in the forests are less than in the open 

 country. Especially does this hold good in the hours of the day and 

 in the seasons of the year in which the greatest heat prevails, the 

 degree of temperature being at these times considerably lower than 

 in. the open country, and, in accordance with this the temperature of 

 the soil in the forest, is considerably below that of the land unshaded 

 by trees. 



" In like manner the degree of humidity in the forest differs from 

 tha,t in the open country ; this being, at all seasons of the year, 

 greater within the forest than it is outside.* 



" In view of these facts, we need not be surprised that the evapora- 

 tion in the forest is found to be much less than it is in the open 

 field ;t and all the more so that, besides the relation of evaporation 

 to temperature, the strength of the wind or movement of the air 

 constitutes an essential element in the operation, and there is pro- 

 portionally much less movement of the air in the forest. 



" In proportion as it is important to obtain a correct determination 

 of the quantity of the rainfall which is lost by evaporation so is it 

 difficult to do so. 



" As the means of making observations on the amount of evapora- 

 tion from the surface of plants and the surface of the ground are 

 different, — besides which, the comparison between the quantity of 

 the rainfall and that of the evaporation is- prejudiced by difference in 



• According to Ebermayer, the difference in the four seasons, from spring onwards 



amounts to 5-7, 9-3, 5-2, and 6-2 per cent. 



f According to Ebermayer, the evaporation from an exposed sufaoe of water in the 



forest was about 64 per cent, less than from one outside the forest 



— ZeiUchrift fur Mtteorologie, viii. 25J. 



