The Subcortical Temperatures of Logs 27 



others have pointed out that in addition to the heating effect of sun- 

 light a certain stimulation from the action of the solar radiation may 

 he observed. The evaporating power of the air, air movements, 

 atmospheric pressure, and precipitation must all play a part in the 

 life of all xylophagous species. 



This article, which is a part of a more extensive piece of work 

 dealing with the ecology of wood-boring insects, will only consider those 

 factors influencing the subcortical temperature of logs. The data for 

 this paper were collected during the summer of 1920 at the field sta- 

 tion of the University of Minnesota Forest School, Itasca Park, Minn. 

 The prosecution of the work was materially aided by the laboratory and 

 other facilities provided by the School of Forestry, and by helpful sug- 

 gestions and criticisms by members of the University Staff, particularly 

 Dr. R. N. Chapman, under whose direction the work was carried on. 



Factors Influencing Temperature 



The attention of entomologists has recently been called to a prac- 

 tical application of solar radiation in the control of wood-boring insects. 

 Craighead,- working with ash logs in several localities in the South, 

 found that the upper side of logs lying in full sunlight often reached a 

 temperature above a point fatal to insects. On the basis of these find- 

 ings he recommends the weekly turning of logs in order to protect 

 them from destructive wood borers. He observed temperatures under 

 the bark of logs which exceeded air temperature by as much as 60 

 degrees (F.?) depending upon the locality, the condition of the sky, 

 and the angle of the sun's rays. He does not mention several other 

 factors which, from the experiments upon which the present paper is 

 based, appear to be extremely important, namely : color, structure, 

 thickness, and surface of the bark, air movements, evaporation from 

 the surface layers of the bark, and proximity to other absorbing or 

 radiating surfaces. 



The principal factors influencing cambium temperatures may be 

 sunmiarized as follows : 



1. Solar radiation 



a. Light intensity 



b. Solar altitude 



c. Angle of incidence 



2 Craighead. P. C. (1920) Direct Sunlight as a Factor in Forest Insect Control. 

 Proc. of the Ent. Soc. of Washington, Vol. 22, pp. 106-108. 



