The Subcortical Temperatures of Logs 41 



TABLE III 



Preceding Air Actuallog °C.above 



weather Date Spec'es Light temp. temp, air temp. 



From Table III it would appear that moisture evaporating from 

 the surface layers of the bark may hold down the temperature within 

 the log to an appreciable degree. 



Conclusion 



As a result of this work it appears that in many instances the 

 weekly turning of logs, as recommended by Craighead, would be effec- 

 tive in destroying many wood-boring insects. This is particularly true 

 of logs with moderately thin dark colored bark. It is equally evident 

 from the discussion that the method does not apply in all cases, as 

 some logs will remain below the temperature fatal to insects even on 

 very bright warm days. 



In using this method it mtist be remembered that it is not only 

 necessary to put the logs in the sun. but it is also important to con- 

 sider the position of the log with reference to the sun. The question 

 of how far the log should be turned each time depends largely upon 

 the position of the log. Logs lying east and west will often reach a 

 higher temperature in a small area than logs lying north and south, 

 but the latter will be heated over a luuch greater surface. 



Summary 



1. In bright sunlight, subcortical temperature on the upper side 

 of moderately thin barked logs often passes above a point fatal to the 

 insect inhabitants of the log. 



