DECAY IN DOUGLAS FIR. 5 
greater than the ratio of infected trees would indicate. For example, 
only about one-third more trees are infected with conk-rot than with 
red-brown butt-roc. yet the board-foot volume of decay is slightly 
more than IS times as great. Conk-rot is usually quite extensive in 
an infected tree, particularly in the mechantable portion of the bole. 
Table 2. — Relative importayice of the different hinds of decay in Douglas fir. 
Volume of decay, 
percentage of gross 
volume. 
Infected 
trees, 
percent- 
age of 
total. 
Infections. 
X umber 
basis. 
Percent- 
age of 
total. 
Average 
Board 
feei. 
volume. 
Board Cubic 
feet. feet. 
Cubic 
feet. 
Cnnk-rof 
3S.4 \ 22.5 
2.7 1.3 
2.1 1.2 
l.fi 1.0 
.1 .1 
61.0 
5.9 
40.2 
22.5 
IS. 9 
118 
15 
70 
46 
35 
41.6 663 
369 
24.6 i 62 
16.2 i 72 
12.3 ! 4 
64.2 
Trr.nk-rot 
28.7 
B ut t-rot 
5.9 
Top-rot 
7.0 
Unknown rots 
1.0 
44. 9 26. 1 
87.6 
284 
323 1 
30.9 
While only a few trees showed brown trunk-rot in comparison to 
those with red-brown butt-rot and yellow-brown top-rot, yet the 
volume of brown trunk-rot is greater than either of the others, 
particularly in board feet. This is due to the fact that brown trunk- 
rot when it does occur is quite likely to cause the loss of all or most 
of the merchantable portion of the affected tree. Yellow-brown top- 
rot and red-brown butt-rot, being localized, result in much less loss 
per tree, but make up for this in the many more trees with these 
decays. The greater loss through brown trunk-rot in board feet as 
compared to cubic feet in relation to red-brown butt-rot and yellow- 
brown top-rot is understood when it is remembered that the former 
is usually in the merchantable portion of the tree, while the latter 
two are often in the stump and top, which are not included in the 
board-foot volume but are figured in computing the cubic-foot volume. 
Furthermore, red-brown butt-rot is of more importance than the 
figures would indicate, since seriously affected trees are quite subject 
to windfall, breaking off near the ground. Then. too. this decay 
destroys the valuable heartwood of the butt logs. 
Of the total of 169 trees, 21 were free from decay, while in the 
remaining 148 there were 284 infections, or an average of 1.9 infections 
per infected tree. Some trees had as many as 6 individual infections. 
Again, in considering the infections conk-rot stands out both in the 
number of infections and particularly in the average volume of 
decay per infection. Trunk-rot has a high average volu tie of 
decay per infection, which shows again that this rot is of minor 
importance only because of the limited number of infections, but 
when a tree is once attacked destructive and extensive decay usually 
results. 
MECHANICAL INJURIES. 
Mechanical injuries on trees are of importance in that besides some- 
times reducing the annual increment or causing an actual Los 
merchantable volume from the mere presence of the injury they 
afford access to the heartwood of the tree for the spores of w< 
destroying fungi. 
