30 COMPOSITE TYPE ON THE APACHE NATIONAL FOREST. 



a thinning should be made, and, if it can be done without too great 

 expense, trees down to a diameter of 12 inches removed. Trees of 

 inferior species should be discriminated against. Except where 

 there is no competition from more valuable species, white fir and 

 Mexican white pine should be cut to the lowest diameter limit at 

 which they can be utilized. Unhealthy trees of all species which 

 seem likely to die before the second cut should be removed. No 

 insect-infected or diseased trees should be left standing, even though 

 valueless. From one-half to two-thirds of the present merchantable 

 stand can safely be removed. If this is done, and taking into account 

 increased growth after cutting, a second cutting can be made in from 

 40 to 50 years. The amount of timber to be removed at this time 

 will not be as great as at the first cutting, because there will be practi- 

 cally no overmature trees. However, the percentage of growth for 

 the stand will be greater. 



ROTATION. 



To determine definitely the rotation for a virgin stand, it is neces- 

 sary to know not only the number of trees per acre of each diameter 

 class which will be left after cutting, but also those which will die 

 from the effects of lumbering and shading before the time of a second 

 cut. The rate of growth after cutting is also desirable. Since, how- 

 ever, only a part of this data is available for the composite type, the 

 rotation can be determined only tentatively. 



The objects of management should of course determine the kind 

 of rotation. Since the aim in this type is to produce the greatest 

 amount and best quality of lumber and to utilize the inferior species 

 and parts for poles, stulls, and lagging, the financial rotation should 

 be employed. The rotation under which the forest yields the highest 

 net returns is well suited to the regeneration of the species. 



However, there is a great difference between the financial rotation 

 and the rotation of the greatest volume production. The latter 

 coincides with the year in which the mean annual increment culmi- 

 nates. By referring to Table 8 it will be seen that the mean annual 

 increment of yellow pine is still increasing at the age of 360 years. 

 Neither has the mean annual increment reached its maximum in 

 Douglas fir at the age of 320 years nor in spruce at the age of 150 years. 

 Furthermore, the mean annual growth of each species will increase 

 until that time when it is equaled by the current annual growth. 

 Figure 4 shows the age of each species at which the mean annual 

 growth equals the current annual growth. This for western yellow 

 pine is seen to be 377 years, for Douglas fir 382 years, and for spruce 

 240 years. A rotation of this length would no doubt be satisfactory, 

 provided there were no factor of loss to be taken into account. But 

 in a forest of this age the annual loss from windfall and decay would 

 probably amount to as much as the total yearly growth. Obviously 



