38 BULLETIN" 871, IT. S. DEPARTMENT OF AGRICULTURE. 



from the occurrence of the injury until it is completely healed over, 

 and such injuries heal slowly. Wounds heal much more rapidly 

 in young than in mature or overmature trees. 



The causes of wounds are taken up in the order of their importance. 



The most serious wounds, both numerically and in regard to 

 the type of injury, result from fire. It is almost impossible to find 

 a stand of timber anywhere in the Sierra Nevada or Coast Ranges 

 which has not been visited by repeated fires. While the thick 

 bark characteristic of incense cedar combined with the lack of 

 resin in the wood makes it somewhat fire resistant, yet broad fire 

 wounds commencing at ground level, reaching some distance up 

 the trunk, and extending deeply into the heartwood are very fre- 

 quent. These wounds are usually roughly triangular in shape, 

 the base being at ground level and the apex at the top of the extent 

 of the scar on the tree trunk. Considerable loss in merchantable 

 timber results from the actual destruction of the wood, and there 

 must be an appreciable decrease in increment until the tree read- 

 justs itself to the loss in conducting tissue caused by the partial 

 destruction of the sapwood and inner bark, which interferes with 

 the conduction of water and soluble salts from the roots to the 

 foliage and the return of elaborated food from the foliage to the 

 roots. This loss is exceedingly difficult to gauge. Total loss in 

 the merchantable timber occurs when a tree is completely girdled 

 and killed or when the supporting tissue is so weakened by the 

 wound that the tree is blown down. 



Large fire scars or "catfaces" are rarely caused by only one fire, 

 but usually by successive fires, each one hollowing out the heartwood 

 a little more. As many as 10 distinct fires have been found con- 

 tributing to the formation of one catface. As long as the w r ood is 

 completely covered by a charred surface the danger of inoculation by 

 fungous spores is reduced to the minimum, but the wood dries out 

 and checks, forming cracks extending into the unburned w r ood. In 

 time, the charred surface is w r eathered away, and finally the heart- 

 wood is exposed over the greater surface of the catface. Here is offered 

 an excellent place for the entrance of a heartwood-destrojdng fungus. 



Wounded trees make strong efforts to callus over the injury, and 

 this is often accomplished in course of time if the wound is not too 

 large. Very large catfaces, particularly on mature or overmature 

 trees, are rarely healed over. The prevalence of wounds caused by 

 fire may be seen from Table VI. 



Table VI clearly shows that fire injury was much more serious on 

 the intermediate area than on the optimum area. The columns of 

 greatest interest are the third and last. The third column (per- 



