28 



INDIRECT UTILITY OF l-'ORESTS. 



Of more importance than the mean annual temperature is 

 the mean temperature of the four seasons. Here and in all 

 future cases a reduction in the forest is represented as 

 minus (— ), and an increase in the forest over the outside 

 station as plus (+). 



These data show that the difference of temperature is 

 greatest in summer, smallest in winter, and that spring and 

 autumn stand about half-way. As to the crowns of the 

 trees, the temperature is even slightly higher in winter than 

 that of the air outside. 



It is of interest to examine the maximum and minimum 

 temperature during the twenty-four hours of the day. The 

 following figures give the differences calculated from the 

 Bavarian and Wiirtembergian observations : — 



