DETERIORATION OF WESTERN YELLOW PINE. 



first began along the checks and then spread over the entire sap- 

 wood. If stained sapwood is considered a defect the loss for Table 1 

 after one season of exposure would amount to 78 per cent in the trees 

 cut in April, 1921, and 67 per cent in the trees felled in December, 

 1920. This difference may be mere chance or it may indicate that the 

 winter-felled trees for some unknown reason were less susceptible to 

 discoloration by the time that climatic conditions in spring or sum- 

 mer favorable for staining arrived. Observations made on wind- 

 thrown yellow pine in this region showed that heavy staining began 

 in July. To avoid sap-stain as much as possible trees should be 

 logged before that time. 



That the principal causes of deterioration were relatively few and 

 well denned is shown in Table 2. 



The most important cause of cull in the trees exposed for one 

 season was checks. Checks were confined mostly to the sapwood 

 but in some cases extended deep into the heartwood. 



Table 2. — Causes of deterioration of felled yelloic-pine trees in Klamath 



County, Oreg, 





Seasons 



of 

 exposure. 



Cull (percentage of gross volume.) 





When cut. 



Checks. 



1 1 1 

 «,„„ _. f Heart- Broken , T> lirr , oH 

 Sap-rot. ? rot> | in felling.. Burned - 



Borers. 



1 



2 



3 



4 



. . , 



8 



April, 1921 



1 

 1 

 2 

 2 

 3 

 4 

 5 

 6 

 7 



13.7 

 16.2 

 16.9 

 11.5 







December, 1920 



1.5 

 24.6 

 57.3 

 59.4 

 63.4 

 53.2 



0.2 0.3 





February ,'l920 



21.9 







3.7 3.2 





Spring of 1919 



9.6 1.2 11.1 

 4. 2 





Spring of 1918.. 







April, 1917 



i.i 



3.9 

 .3 



15. .5 9. fi 



1.9 



Spring of 1916 



63.7 14.1 .8 8.3 





Spring of 1915 



57.0 



30.3 5.8 







i ! 





Checking usually began and was most severe on the side of the 

 trunk expo'sed to the direct rays of the sun. Exceptions to this rule 

 were found where particularly intense heat had caused severe check- 

 ing when the bark was burned. Normally the loss through checking 

 in any one tree resulted from several or numerous checks, but in a 

 very spiral grained tree a single deep check twisting around the tree 

 sometimes caused all the loss. Considering column 3 of Table 2 it 

 would seem that the loss through checking decreases with the length 

 of exposure after the second season, while it is self-evident that this 

 loss should increase slightly or remain about the same. The explana- 

 tion is that as sap-rot becomes more severe the checks become obscure 

 or disappear completely, and in scaling the loss from this source is 

 then difficult to separate from that caused by sap-rot. 



There was little sap-rot during the first season. In fact, the en- 

 tire 170 board feet given in Table 2 were obtained from a single tree. 

 But bj the end of the second season the loss from this cause was 

 heavy and continued so. After that time sap-rot was the most im- 

 portant factor in deterioration. In poles and young thrifty stand- 

 ards~with wide sapwood, sap-rot by amounting to two-thirds or more 

 of the gross volume often caused the loss of the entire tree. It fol- 



