60 BULLETIN 275, U. S. DEPARTMENT OF AGRICULTURE. 



number of other so-called inferior species, the pathological-rotation 

 age is presumably lower than the age of maximum-volume pro- 

 duction. We must look to forest mensuration for final data to settle 

 this point. 



Barrington Moore * advocates a rotation based on the " period dur- 

 ing which the rate of volume production is greatest or shortly after 

 it, provided it is long enough to give the most valuable product." 2 

 Here, again, the pathological rotation will be the limiting factor, 

 except for species in which the rate of greatest volume production 

 possibly occurs at a lower age than the pathological rotation. That 

 the value of lumber grades is bound to play a far more important 

 r61e in the future than at present, with regard to rotation, is a fore- 

 gone conclusion. 



So far, we have considered only the rotation per species. In pure 

 or almost pure stands the rotation of the unit is determined by the 

 rotation of the species clearly dominating, not only numerically, but 

 also in value. 



As soon as two or more equally valuable commercial species appear 

 together in about the same proportion, the rotation of the stand 

 becomes " synthetic;" that is, the rotation for the unit is governed 

 by the individual rotations per species. In the great majority of 

 cases neither the representation of the species nor their individual 

 values are the same. Nearly always there will be certain species 

 more desirable than others, which latter then are classed as more or 

 less inferior. A weak representation of inferior species with low 

 pathological rotation will be without much effect upon the synthetic 

 rotation of the unit. The stronger the representation of inferior 

 species, the heavier will be their bearing on the synthetic rotation. 



On many of the large private holdings of the West the inferior 

 species are disregarded altogether; they are simply left standing in 

 logging operations. Unless the logged-over area is burned, the 

 representation of inferior species is then an unduly heavy one. They 

 must necessarily dominate the stand in the future. 



The national forests, on the other hand, will be the regulated for- 

 ests of the future. In many of the national forests, particularly in 

 the West, several species of unequal value are represented on the 

 same unit in such a manner as to make each one a strong factor to be 

 considered. Here, regulation of yield must be based upon synthetic 

 rotation and synthetic cutting cycles. Rotation and cutting cycles 

 for each species must be determined separately, each on the chosen 

 basis of either maximum-volume production, or rate of maximum- 

 volume production, or production of maximum value, limited in 



1 Moore, Barrington. Chapman's method of studying yield, p. 94, 1913. To accompany forest plan, 

 Plumas National Forest, district 5. Appendix (continued), Silviculture. (Unpublished. Furnished by 

 courtesy of the U. S. Forest Service.) 



2 See also Zon, Raphael, Balsam fir, U. S. Dept. Agr., Bui. 55, 68 pp., 2 pis., 8 figs., 1914. (See p. 67.) 



