EFFECT OF FORESTS ON MOISTURE. 



•6b 



the air. Although the humidity of the air depends, in the 

 first place, upon the general distribution of heat and air 

 pressure over the large sheets of water on the earth which 

 governs, the direction and force of the moist air currents, the 

 vegetation of the earth also affects the degree of humidity, 

 chiefly because it reduces the temperature locally. That 

 effect may be felt in the degree of humidity of the air, the 

 amount of precipitation, the degree of evaporation and in the 

 feeding of springs and rivers. 



a. Hunddilij of the Air. 



The observations so far available show that forests do not 

 affect the absolute humidity of the air to any appreciable 

 extent. Those made in Bavaria yielded the following 

 results : — 



These figures show that the increase in the forest did not 

 reach 2 per cent, of the quantity outside. More extended 

 observations have since shown that the difference is even 

 smaller, and in some cases forest air has been found to 

 contain less absolute vapour tension than open air. 



It is different with the relative humidity of the air. As 

 the temperature of forest air is on the whole lower than that 

 of open air, while the absolute humidity remains about the 

 same, it follows that the relative humidity of forest air should 



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