832 BULLETIN 426, U. S. DEPARTMENT OF AGRICULTURE. 
Studies of the grades cut from pine logs of various dimensions indi- 
cate that knotty trees under 32 inches in diameter produce largely 
common and box lumber, which can be marketed at present only at a 
loss or at a very shght profit. Such trees may profitably be left for 
seed or protection and to form a part of the next cut, for which they 
will be more valuable because of increased growth, higher selling 
prices, and a greater percentage of high-grade product as the result _ 
of natural pruning. 
The white fir and cedar in sugar-pine stands are now difficult to 
market at a profit above the bare cost of production. Both of these 
species have greater prospective than present values—the former for 
pulp as well as lumber, the latter for pencil stock and other refined 
uses. It appears to be wise management, therefore, to remove only 
the dead, diseased, and mature trees which will not remain mer- 
chantable until the next cut. Young sugar pine reproduction 
requires shade in youth, and these species are left to furnish it in 
preference to others of more value. Their reproduction will endure 
shade, and is therefore a valuable agent in preventing brush from 
securing control of cut-over areas. 
In applying the above principles on National Forests the cutting is 
so regulated as to create conditions favorable to the securing of a 
stand of young trees through natural regeneration, because the per- 
petuation of the forest depends upon this. Sugar-pine seed is eaten 
in large quantities by rodents and birds, and since young trees 
require protection from too severe light for the first 10 years of their 
life the securing of young growth is rather a difficult problem. 
Eventuaily, when transportation and market conditions allow of cut- 
ting over areas frequently for a small volume of timber, the shelter- 
wood system of-cutting will probahly be applied where sugar pine 
makes up 20 per cent or more of the stand. This system provides for 
several successive operations separated by short intervals; the first 
opens up the stand slightly to afford just sufficient heht to stimulate 
the seed-producing capacity of the remaining trees and to secure young 
growth; the second follows after reproduction has been secured 
and partially frees it from shade; the third removes the remaining 
mature trees. At present, however, this system would not pay. 
In the sugar-pine type the forest is made up of groups of mature 
sugar pine and its common associates, interspersed with openings and 
approximately even-aged groups of younger trees of the same com- 
position, as weil as of trees of various ages al nd species occurring 
singly. On areas where the occurrence is in groups the clumps of 
mature trees are cut clean and the immature are left. Sometimes it is 
necessary to leave a mature tree which may occur in an immature 
group from which it could not be removed, or to remove a few imma- 
ture trees from mature groups because of the likelihood of wind 
damage or to free reproduction from shade. In cuttings of this 
