EFFECT OF FORESTS OX TEMPERATURE 



29 



It will be observed that the temperature in forests is 

 higher during the night and lower during the da}' than on 

 open ground ; the difference is most pronounced in summer 

 aiui next in autumn. This leads to the conclusion that 

 forests tend to moderate the extremes of heat and cold. In 

 order to illustrate this further, the following data are given 

 which show the difference between the temperature inside 

 and outside the forest in July and Januarj^ respectively the 

 hottest and coldest months of the year. The figures represent 

 the averages of the Prussian observations made during ten 

 years : — 



These figures show that the maximum temperature of 

 forests, situated in a climate like that of Northern Germany, 

 may be lowered in July by 5*87° at 5 feet above the 

 ground, and the lowest temperature in January may be 

 raised by 2*70". The detailed observations of the different 

 stations show further that the above effect depends greatly 

 on the geographical position and the extent to wliich the 

 localities are exposed to, or protected against, air currents. 

 The effect differs also considerably according to species, as the 

 following data will show : — 



Fully stocked beech forests reduce the extremes of the air 

 temperature during July about twice as much as spruce or 



