FOREST PATHOLOGY IN FOREST REGULATION. 49 



an age of 134 years in a suppressed tree. After all, it may be more 

 than a coincidence that the first case of such infection in a sup- 

 pressed tree occurs near the critical age for suppressed white firs in 

 this region. It is within reason to assume that thrifty, uninjured 

 white firs run only the evidently not very great risk of becoming 

 infected through branch stubs. But decay entering through knots 

 is always caused by fungi of a very aggressive character, such as 

 Echinodontium tinctorium, which is not always the case with wounds. 

 As a possible cause of infection we may also mention dead and broken- 

 off leaders or volunteers, the stubs of which are only slowly overgrown. 



It would appear that, if infections of unwounded trees are really 

 so rare, white fir will take care of itself on the managed areas of the 

 future. This would probably be the case in an ideal, 100 per cent 

 normal forest. But this is Utopian. There will always be a certain 

 risk of wounding. Even after the already wounded individuals are 

 eliminated, which will consume a number of decades, it is unreason- 

 able to expect that our forests should then be so much closer to the 

 normal than the best kept European forests are at the present day. 

 How severe the loss from Trametes pini is in the Prussian forests has 

 already been shown. Whatever may be the final verdict as to the 

 age of decline of unwounded thrifty trees in managed forests, it can 

 not be of more than purely theoretical interest to us and the next 

 following generations. We must cope with present-day conditions 

 as we find them, not as we would wish to have them. 



The immense importance of fire in connection with decay appears 

 so plainly from Table II that it is hardly necessary to emphasize the 

 fact. The field notes show that in 59 trees wounded by fire, in only 

 11 was no decay traced to the fire wound. Fire, then, is one of the 

 most important factors in connection with decay; all the more so, 

 as fire generally attacks the butt part of the tree, and decay starting 

 from fire wounds therefore destroys a much greater part of valuable 

 timber than decay in the upper part of the bole. 



Lightning generally results in comparatively light advance rot. 

 From Table II it appears that the only tree in which serious decay 

 could be traced to lightning, and in which it was neither connected 

 with suppression nor with a serious wound from another source, is 

 No. 59, 232 years old. To judge from our data, lightning is rarely 

 connected with typical decay, although it often renders large parts 

 of the tree partly unmerchantable. 



The cumulative risk of wounding is shown in Table II (column 7) 

 by the fact that the cases rated with three crosses become far more 

 frequent after the trees have reached the age of about 90 to 100 years. 

 After they have reached about that age such cases are commonly 

 accompanied by decay. Serious decay follows serious wounding after 

 98035°— Bull. 275—16 4 



