June 14, 1921 
Growth on YeUow Pine Lands in Idaho 
1143 
A striking difference exists between the rate of growth in the cut-over and the 
uncut stands. The cubic volume of the cut-over stands has increased at the 
rate of 5.3 per cent per annum since the plots were established, while the virgin 
stands show an annual increase of only 0.6 per cent for the same period. With 
an indicated annual increment of 24.9 cubic feet per acre it is apparent that the 
loss—by windfall, bark beetles, mistletoe, or otherwise—of one large tree contain¬ 
ing 249 cubic feet would completely offset 10 years’ growth on 1 acre of virgin 
timber. 
The actual average loss was found to be 6.2 cubic feet an acre for the five-year 
period in the cut-over stands and 137.5 cubic feet an acre in the virgin stands 
during the same time. This comparison is gratifying, although the situation 
still demands improvement of silvicultural practice. It is evident that through 
a careful selection of trees to be left standing on cut-over areas the maintenance 
of a desirable rate of volume growth will be made possible. 
The percentage of trees showing lack of vigor, as emphasized by Table III, is 
a good criterion of the general condition of the stands. In this study slight 
injuries were not considered; the tree had to be decidedly lacking in vigor before 
being so classified. For example, Douglas fir which showed light mistletoe infec¬ 
tion or western yellow pine with slight porcupine injury, if otherwise thrifty, were 
still classified as vigorous. Since a general lack of vigor and thrift usually 
precedes death, this will be treated along with mortality. 
Table III.— Defective trees on sample plots in 1918 and 1919 , with summary of 
important causes of lack of vigor , in percentages of total living trees and cubic 
volume at beginning of period 
Cut-over plots 
Nos. 1 to 3 
Virgin plots Nos. 4 to 16 
Cause of lack of vigor 
Western yellow 
pine 
Western yellow 
pine 
Douglas fir 
Total 
Trees 
Cubic 
volume 
Trees 
Cubic 
volume 
Trees 
Cubic 
volume 
Trees 
Cubic 
volume 
Mistletoe infection__ 
Per cent 
Per cent 
Per cent 
Per cent 
Per cent 
3.37 
Per cent 
4 66 
Per cent 
1.59 
Per cent 
1.47 
Suppression... 
Porcupine injury.. 
2.94 
0.57 
1.65 
.65 
0.11 
. 14 
2.35 
.16 
2.01 
.34 
.13 
.10 
Defective tops a... 
Unclassified. 
.37 
.01 
2.81 
1.70 
3.96 
1.10 
.90 
1.80 
1.24 
2.37 
1.91 
1.75 
3.07 
1.44 
Total, all causes. 
3.31 
.58 
6.81 
5.31 
8.42 
8.43 
7.60 
6.21 
° This group includes such conditions as tops broken in logging, spike tops, and stag-headed trees. 
CAUSES OF LOSS 
Table IV is a record of mortality from different causes. Of the agents listed as 
responsible for the death of the trees, the most important are bark beetles, 
windfall, and mistletoe. In many cases large mature and overmature trees were 
killed, resulting in a large volume loss. 
