June 14,1924 
Growth on Yellow Pine Lands in Idaho 
1147 
Economic conditions have improved to some extent, but still only one cut 
will be possible for a long time. The marking rules must frequently be based 
on a compromise between economic necessity in logging practice and the best 
silvicultural practice. 
The distribution of the reserved trees over the area is a matter of great import¬ 
ance. Except for the danger of wind-throw on exposed ridges, it is inadvisable 
to leave groups of trees of any considerable area untouched, since such blocks 
are inimical to both acceleration of growth and even distribution of new re¬ 
production. Leaving trees in groups neutralizes the advantageous effects of 
cutting, and on the better sites may interfere with western yellow pine reproduc¬ 
tion. Great care should be exercised in selecting trees for increased volume 
growth and enhanced quality of the subsequent cut. These conclusions have 
been substantiated by Dunning's studies (1 , 2) in California. He has also clearly 
pointed out that the crown furnishes the most reliable criterion of what may be 
expected from reserved trees. A dense, bright-green, pointed crown is indicative 
of a thrifty tree. Trees with long narrow crowns are generally growing more 
rapidly than average trees of the same size. As a general principle, it is undesir¬ 
able to leave mature or overmature seed trees because even on the best sites 
the death of one large tree will greatly reduce the net increment and the loss 
will be material of the highest quality. Furthermore, satisfactory growth can 
not be expected from trees of either western yellow pine or Douglas fir over 30 
inches in diameter, even on the best sites in this region. 
The marking practice in effect in the central Idaho forests is, in many 
respects, quite similar to that outlined by Munger ( 8 ) under the selection system 
or a modified form of it for the management of the western yellow pine type in east¬ 
ern Oregon. The present marking practice in central Idaho provides for reserving 
a considerable nucleus of vigorous immature standards and a sufficient number 
of sound, thrifty mature trees to make up the necessary quota. These may be 
desired for the purpose of maintaining the continuity of the forest cover, for 
increased volume and value increment in a second cut, or to insure adequate 
seed for regenerating the stand. All defective, diseased, and suppressed trees 
should be marked for cutting unless needed as fire insurance or seed trees. No 
defective or diseased tree should be left standing if it is evident that it will not 
live until the next cutting, unless it is absolutely needed for silvicultural purposes. 
When it becomes necessary to reserve trees among the larger diameter classes, 
vigorous, thrifty trees of good form and development should be selected. It is 
thus evident that the marking on each individual area must be varied to meet 
the silvicultural requirements of the forest. The importance of careful, intelli¬ 
gent marking of timber on cutting areas can not be overemphasized, since this 
is the means by which rational silvicultural management is actually secured 
in practice. 
SUMMARY 
This report presents the first important results of a growth study which is 
still incomplete. Permanent sample plots are used to compare cut-over and 
virgin forests as to condition of stands, mortality, and increment. The cut¬ 
over areas are in a much thriftier and more vigorous condition. In the virgin 
stands the loss of vigor is caused principally by bark-beetle infestations, mistletoe 
infection of Douglas fir, wind-throw, and suppression. These causes of loss 
were largely eliminated from the cut-over stands. Porcupines are responsible 
for a relatively small amount of injury. 
The average rate of net volume growth in relation to the volume of the stand 
is strikingly greater in the cut-over than in the virgin stands. In the latter, the 
annual loss through death and decay practically nullifies the annual growth. 
