Management of Western Ycllozv Pine. 55 



proximately the age prescribed in the rotation. Under the selec- 

 tion or group selection system the age at which the different trees 

 are cut will vary widely in spite of all efforts to the contrary. 

 The rotation is, however, of considerable importance in regu- 

 lating the cut ; and, considering large areas, the average age of the 

 trees cut (after the first period) should not differ greatly from 

 the rotation. 



In deciding upon a rotation the accuracy of the growth figures 

 will have some weight. Thus if the figures are rough the rota- 

 tion will generally have to be longer than the figures indicate, so 

 that if a mistake is made it will be on the safe side. If the 

 figures are fairly accurate they can be used directly. In the 

 southwest a rotation of about 200 years will be best for the 

 present. Later on this may be shortened. Any rotation, it must 

 be remembered, will give trees larger than the average on good 

 sites and smaller than the average on poor sites. Thus on the 

 Gila National Forest a rotation of 160 years will give trees 26.6 

 "D. B. H. on Quality I, and trees 19.85" on Qualities II and III. 

 Although these diameters are large enough for good saw timber, 

 a rotation of 200 years has been used. 



With the felling period the important point to remember is that 

 the shorter the period the lighter will be the cut, and vice versa. 

 Hence the length of the period must depend almost entirely on 

 market conditions and the accessibility of the area. Obviously, 

 the more remote the area the heavier must be the cut, and con- 

 sequently the longer the felling period. The maximum length 

 will be governed by the maximum cut which can be made without 

 injuring the chances of reproduction. In the Southwest a fell- 

 ing period of about 30 years will be about right where the area is 

 readily accessible, and 50 years where it is of difficult accessi- 

 bility. 



The number of felling periods in the rotation will eventually 

 determine the number of broad age classes into which the groups 

 will be divided ; e. g. with a rotation of 200 years and a felling 

 period of 40 years the stand will eventually be composed of 

 groups each representing one of five age classes. 



