FOREST PATHOLOGY IN" FOREST REGULATION. 47 



very pronounced cases appear in the same year. They seem to be- 

 come particularly common from about 110 to 120 years. 



Suppression stands out strongly as an important factor. Out of 

 the total of 97 cull cases, 66 are connected with suppression. Consider- 

 ing that our average volumes over ages were curved from figures 

 which were rather low and that the intermediate white firs in a virgin 

 uneven-aged mixed stand are rather to be considered as recovering 

 suppressed trees than as dominants decreasing in rate of height growth 

 the intermediate class may consistently be added to the suppressed, 

 giving 73 in all, or about 75 per cent. Suppression is commonly con- 

 nected with a more or less high decay rating, provided the tree is 

 wounded seriously. Again, low-volume trees with marked decay are 

 more liable to be a total loss on account of their form. A rot volume 

 percentage of 50, for instance, leaves still a good deal of merchantable 

 stuff in a tree with high volume, but it would make a small tree com- 

 pletely unmerchantable. In the comparatively few cases where 

 dominant trees show decay, the wounding is either of very momentous 

 character or the decay is more or less insignificant and localized near 

 the scars. This is true at least for the younger trees. 



In glancing over the decay column we see that the higher ratings, 

 xx and xxx, begin rather suddenly to become more frequent after the 

 trees have reached the age of about 123 to 126 years; after the age of 

 about 129 or 130 years they become very common. While decay 

 in the broadest sense of the word may show in trees 60 years old and 

 perhaps younger, the critical age of white fir with regard to more 

 serious decay appears to lie at about 130 years, at least for the region 

 investigated, taking into account that we have to deal here with a 

 practically virgin stand grown up under the cumulative risk from 

 suppression, frost, lightning, and the other factors of influence. 

 Decay of any consequence appears at this age in trees with a combina- 

 tion of wounding and suppression. In the few apparent exceptions 

 the decay is localized near unusually large wounds. 



We find, further, that up to about 150 (148) years in badly wounded 

 but dominant thrifty trees the decay is either not very far advanced 

 iu degree, if in extent, or that the wounding is of quite extraordinarily 

 severe character. 



Tree No. 19, age 132, seems to form an exception, but we will see 

 later that frost cracks, though not offering a large opening by virtue 

 of their length, are instrumental in the longitudinal advance of the 

 decay. It seems that after about 150 years thriftiness as expressed 

 by dominance is less able to outbalance the influence of serious 

 grounding. 



Jf it is al .ill permissible to draw any inference from the compara- 

 tively small amount of material at band, we may distinguish throe 

 critical stages in the life history of wounded white-fir trees, and we 



