FOREST PATHOLOGY IN FOREST REGULATION. 9 



amount of timber contained in the few overholders left as seed trees 

 and in individuals at or just below the diameter limit established in a 

 first cutting would prove attractive to purchasers of the future, pro- 

 vided always no change in the lumber market should take place. 

 The diameter limit now fixed on many national forests may be said 

 to be about 12 inches, varying somewhat with the species and local 

 conditions. Few trees below this diameter will reach such dimen- 

 sions in 50 years as to form a merchantable stand, judged by our 

 standards of to-day. 



If it is unwise blindly to take over principles and policies developed 

 and more or less accepted in countries with old-established and far- 

 advanced forestry and apply them to the first stages in the organiza- 

 tion of our virgin forests, the study of the history of the forestry 

 movement and development in other countries can not but be of the 

 greatest practical value. We are justified also in assuming that the 

 history of forestry will repeat itself and that forestry in all countries 

 with large virgin or practically virgin forests in touch with the gen- 

 eral market will run through the same phases of development as it 

 did during the last centuries in central Europe, but at a very much 

 faster pace, owing to the enormously enhanced facilities of transpor- 

 tation and marketing and the rapidly increasing demand for timber. 



If this be true, a cutting cycle of about 50 years may prove too 

 long. To judge from the development of timber values in Europe, 

 our once cut-over stands should prove attractive in a shorter period. 



In determining the duration of cutting cycles, it is reasoned that 

 the accessible virgin timber in the national forests should be cut once 

 before operations return to the first areas logged over. How much 

 time this first culling may consume we have no means of telling. It 

 should be remembered, however, that the system naturally present- 

 ing itself is that of selection cutting, and although there is a decided 

 tendency toward heavier marking approaching clean cutting, this 

 latter should be taken cum grano salis. Actually, the reproduction 

 left includes all individuals up to and sometimes beyond 12 inches 

 diameter breast high; that is, trees that have reached a considerable 

 age and that in 50 years will have grown to what would be classed in 

 European forestry as veterans. 



CUMULATIVE RISK. 



In fixing long-term cutting cycles, a most important point has not 

 been sufficiently emphasized, namely, the " cumulative risk" from fire, 

 windfall, frost, and so-called deterioration to which a given stand is 

 exposed during so long a period. The longer the cycle the greater 

 the ratio of risk. The unparalleled development of fire protection 

 in the national forests of the United States, it is true, promises fairly to 

 exclude actual destruction from fire on any large scale; but, as long as 



