1144 
Joumal of Agricvltural Research voi. xxvm, No. n 
Table IV. — -Causes of death of trees 4 inches diameter breast high, and over, in 
percentages of total living trees and cubic volume at the beginning of period a 
Cut-over plots 
Nos. 1 to 3 
Virgin plots Nos. 4 to 16 
Cause of death 
Western yellow 
pine 
Western yellow 
pine 
Douglas fir 
Total 
Trees 
Cubic 
volume 
Trees 
Cubic 
volume 
Trees 
Cubic 
volume 
Trees 
Cubic 
volume 
Windfall___ 
Per cent 
Per cent 
Per cent 
0.44 
Per cent 
8.65 
Per cent 
0.75 
Per cent 
0.63 
Per cent 
0.59 
Per cent 
0. 65 
Insects____ 
2.49 
2.85 
.46 
.97 
1.50 
2.27 
Mistletoe__ 
.29 
.27 
. 14 
.08 
Suppression. 
.39 
.01 
.35 
.02 
.37 
.02 
Logging... 
0.48 
0.09 
Porcupines__ 
. 11 
.001 
.06 
.002 
Unclassified_ . 
.96 
1.07 
.33 
.29 
1.33 
.24 
.82 
.28 
Total--.. 
1.44 
1.16 
3.76 
3.811 
3.18 
2.13 
3.48 
3. 302 
a This includes only those trees which died since the plots were established. 
A maximum loss of 12.87 per cent in the five-year period was found on one 
uncut plot. Although this loss was occasioned by the death of three large over¬ 
mature trees, it is nevertheless alarming. Table IV shows that insect attacks, 
particularly those of the western pine beetle (Dendroctonus brevicomis ), are 
responsible for a volume loss over twice as great as that caused by all other 
agents, and that this has been confined to the virgin stands and to the killing of 
individuals or small groups of trees. Under normal conditions the infestations 
are often sporadic, threatening for a year or two, and then decreasing. However, 
while no serious epidemics have occurred in recent years in this locality, it must 
not be forgotten that this insect is very destructive to western yellow pine 
throughout the West and constitutes a real menace which, from time to time, 
assumes very serious proportions, possibly aggravated by the advent of favorable 
climatic conditions. Practically all the insect injury noted occurred in trees 
above the sapling stage, and sufficient insect activity has been shown in virgin 
stands to warrant foresters giving it careful attention. 
On these plots windfall was confined to the mature and overmature trees in 
the larger diameter classes. On the national forest timber sales this is being 
partially controlled through the selection of wind-firm individuals for seed trees 
and through the removal of very tall trees on exposed situations after adjoining 
trees which protect them are cut. As a matter of fact, wind-throw here was not 
nearly as serious as it appears to have been in the Whitman National Forest in 
eastern Oregon (11). 2 It is gratifying to note that no wind-throw occurred on the 
cut-over plots. Since a large proportion of the windfall occurs within four or 
five years after cutting and the remainder in rapidly decreasing amounts, the 
exercise of reasonable precaution in marking will undoubtedly eliminate the 
danger of heavy loss. 
Western yellow pine in the vicinity of these sample plots is not infected with 
mistletoe (Razoumofskya campylopoda), although on the basaltic soils of the wes¬ 
tern division of the Payette National Forest and the nearby Weiser National 
Forest heavy infections occur. There is a suggestion here of an interesting 
causal relation between soil type and the local distribution of mistletoe, although 
the significance and constancy have not been determined. Douglas fir is fre¬ 
quently infected with mistletoe (Razoumofskya douglasii). Indeed, on plot No. 8 
2 Reference is made by number (italic) to “Literature cited,” p. 1148. 
