FOREST PATHOLOGY IN FOREST REGULATION. 61 



every case by the age of decline. The synthetic rotation is figured 

 on the basis of the specific rotations, under due consideration of rep- 

 resentation and relative value of each species from a commercial and 

 silvical point of view. The same is true for cutting cycles. It should 

 not prove impossible to express both representation and relative 

 value for each species in symbols, which, together with the specific 

 rotation, would permit the balancing of each species against the 

 others, and thus to arrive at the synthetic rotation of the entire unit. 

 In this way the inferior species will be given their proper place in for- 

 est regulation. This procedure is undoubtedly followed more or less 

 consciously wherever regulation is planned by way of timber sales. 

 It can not be reduced to a practical working system, however, until 

 all factors upon which it is based are thoroughly known. 



The pathological rotation limits the rotation of white fir, on the 

 basis of our present knowledge, to 150 years — at least during the 

 transition period. Perhaps the actual felling age for the species will 

 be shortened long before that time arrives. The chances of pro- 

 viding for the next decades are distinctly better. On areas cut over 

 to-day we may expect second operations in not too remote a future, 

 taking the place of a second improvement felling. Provided our figures 

 prove correct, the critical age and the age of decline will be a safe 

 guide in tentatively fixing cutting cycles for white fir, which, together 

 with the cutting cycles for the other species present, will permit the 

 establishment of the synthetic cutting cycle for the unit. 



Our present knowledge of the pathology of white fir leads us to the 

 following practical conclusions for the period of transition: 



Prejudice against white fir as an inferior species. 



Conservative scaling (excluding advance roc) in favor of the purchaser on the one 

 hand and of better utilization of sound white fir (where market conditions 

 permit) on the other will in time overcome the prejudice . 

 Silvicultural treatment of white fir. 



Reproduction: Frost and lightning zones are to be avoided. 

 Marking on timber sales: 



On frost and lightning zones marking should be heavy. 



Badly wounded trees,' particularly those with open fire scars or frost cracks, 



should be marked heavily. 

 Badly suppressed trees should be marked heavily. 



Trees with a combination of wounds and suppression can not be figured on 

 to remain fairly sound beyond the critical age of about 130 years. The age 

 of such trees, if left standing, added to the number of years to elapse before 

 the presumable next cutting takes place, must not exceed 130 years. 

 Trees wounded, though thrifty, can not be counted on to remain sound 

 beyond the age of decline of about 150 years. The age of such trees, if left 

 standing, added to the number of years to elapse before the presumable 

 next cutting takes place, must not exceed 150 years. 

 Rotation and cutting cycles. 



The rotation for white fir, as far as we can judge now, can not exceed 150 



years. 

 Cutting cycles for white fir must be limited by the age of decline. 



