EFFECT OF FORESTS ON TExMPERATURE. 



IMi 



positions half way. It should also be noted that in spring 

 the temperature sinks from the surface down to 4 feet, and 

 in autumn the reverse takes place,* due to the fact that the 

 changes of temperature at the surface of the ground are only 

 slowly transmitted to the lower layers of soil. 



The effect differs considerably in the case of different species. 

 In this respect the Swiss observations, average of 12 years, 

 have yielded the following results : — 



The evergreen spruce reduces the temperature of the soil 

 considerably more than the deciduous beech, and still more 

 so than the larch. This difference is very important in 

 spring, as it delays the commencemewt of the annual cycle 

 of growth and reduces the danger from late frosts. 



c. Temperature of Trees. 



Another point of interest is that the temperature of living 

 trees varies from that of the surrounding air. 



The following differences have been found in Bavaria, in 

 degrees Fahr. 



Spring. Summer. Autumn. Winter. Mean. 

 At :> feet from the ground = -2-27 -315 -1-19 -2-29 -2-21 

 III the crown of the trees = 1-48 -2-11 - "67 - -72 -1-24 



In Switzerland, the following differences were observed, 

 annual averages : — 



In beech woods = 

 In larch woods = 

 In spruce woods = 



- 2-92 



- 3-04 



- 4-79 



* This is seen from the actual temperatures, which are not given here. 

 M.F. 1> 



