EFFECT OF FORESTS ON MOISTURE. 



89 



accounted for by an increased formation of dew which is 

 registered together wuth the rainfall. 



On the whole, it may be said that various physical factors 

 act towards rendering forests excellent condensers of vapour, 

 because they have a lower temperature, a moister air and 

 break the force of air currents. These properties are more 

 evident in elevated positions than in low lands and in the 

 vicinity of the sea, where tliey are swamped by other more 

 powerful agencies. Al)solute certainty in respect of these 

 phenomena can only be obtained through further extensive 

 observations. 



The presence of a forest crop prevents a portion of the 

 rainfall from reaching the ground, because it is intercepted by 

 tlie crowns of the trees. The various measurements have 

 yielded the following results : — 



The average of the Bavarian stations shows 77 per cent, 

 of the rainfall as having reached the ground, whereas 

 23 per cent, were intercepted by the crowns of the trees and 

 evaporated or partly ran down the trunks of the trees ; the 

 latter has been found to vary from 1 per cent, to 13 per cent., 

 according to species and the total rainfall. 



c. Evajwralion. 



Owing to the lower temperature, the somewhat greater 

 humidity of the air and the quieter state of the atmosphere, 

 evaporation must be considerably smaller in forests than in 

 the open. This has been conclusively proved l)y direct 



