24 BULLETIN" 14! 
hewed railroad ties, mine timbers, and mine props. The making of 
hewed railroad ties on an extensive scale, however, usually produces 
as a by-product a supply of mine-prop material (pi. 2) entirely out 
of proportion to the quantity the market can absorb, so that even on 
areas privately owned lodgepole is seldom cut clear. Very much the 
same condition obtains in the Douglas fir type. 
Cut-over areas in the lodgepole type are usually left in a nonuni- 
form condition. Tie-size trees are seldom to be found ; on some areas 
the small, prop-size material has been cut and the saw timber left, 
and on others saw timber has been taken and the smaller trees have 
been left ; on a very few areas only has all material down to mine- 
prop size (4 inches in diameter) been removed. In addition to trees 
of poor form and defective trees on lodgepole and Douglas fir cut- 
tings, a quantity of reproduction, saplings, and small poles almost 
invariably remains, assuring at least a scattered stand for the produc ■ 
tion of seed, and young growth sufficient to provide future cuts. 
In the Engelmann spruce type the fact that there is usually no 
market for trees less than 10 inches in diameter at breast height gives 
assurance ordinarily that sufficient immature trees will remain after 
cutting to maintain productivity. However, on rather restricted 
areas where stands are made up almost wholly of large trees, an in- 
sufficient number of smaller ones may remain to insure perpetuation 
of the forest. In such places it is important that a partial cover be 
retained to furnish seed and provide shade for reproduction, even 
though the trees left may be of merchantable size and not capable of 
increased growth. Since Engelmann spruce is naturally subject to 
wind throw, careful attention must be given to selecting the shorter, 
windfirm specimens for this purpose. 
CHIEF CONSIDERATIONS GOVERNING CUTTING 
CUTTING AT MATURITY 
In generaj, trees should be cut as nearly as possible at the time when 
the mean annual growth (or the quotient of the volume of the tree 
divided by its age) begins to decline. This, of course, does not 
coincide with the time of greatest diameter growth, since on a tree 
of large circumference the later, narrower growth rings may indicate 
a greater volume growth than do the wider rings near the center. 
The criterion is volume growth, not diameter growth. When growth 
ceases to increase satisfactorily, the tree should ordinarily be har- 
vested. It is at this point considered to be mature. 
Table 2, prepared by C. G. Bates, from local volume tables for 
Engelmann spruce, is generally appjicable for the region, and illus- 
trates this point. It will be helpful in determining the maturity of 
any tree. 
