12 
BULLETIN 799, U. S. DEPARTMENT OF AGRICULTURE. 
decay is present in the tree examined, and this fact would tend to 
place the age of earliest infection somewhat below the age of the 
tree at the time visible decay is noted. 
Table IV. — Relation of rot to age classes, with reference to the infection age 
of icestern ichite pine on sites of the oottom and slope types. 
Bottom sites. 
Slope sites. 
Age class. 
Average 
age 
(years). 
Number of trees (basis). 
Aver- 
age rot 
per in- 
fected 
tree' 
(cubic 
feet). 
Average 
age 
(years). 
Number of trees (basis). 
Aver- 
aee rot 
Total. 
In- 
fected. 
Per- 
centage 
in- 
fected. 
Total. 
In- 
fected. 
Per- 
centage 
in- 
fected. 
per in- 
fected 
tree 
(cubic 
feet). 
41 to 50 years 
51 to 60 years 
61 to 70 years 
71 to 80 years 
81 to 90 years 
91 to 100" years 
48 
56 
66 
80 
85 
94 
16 
21 
21 
41 
80 
36 



4 
26 
17 



10 
33 
47 



.79 
1.78 
1.38 
45 
56 
63 
74 
85 
95 
33 
17 
48 
12 
46 
52 


2 
2 
10 
13 


4 
17 
22 
25 


.035 
.075 
.213 
.145 
In Table IV the youngest trees found visibly infected on the slope 
site are in the 61 to 70 age class, and the age of the earliest infection 
would be found in the 51 to 60 age class. The youngest tree on the 
slope sites found to have visible decay is 61 years old. From these 
data it appears that the age of the earliest infection would be found 
between the ages of 50 and 60 years, and to be reasonably safe it may 
be placed at approximately 50 years. 
Most of the answers received from the logging companies in refer- 
ence to the question of the age at which western white pine is first 
infected give 50 years as the approximate age below which very 
little infection occurs. 
It is apparent that factors other than that of site influence the per- 
centage of infections as expressed by the figures in Table I. On the 
bottom site (Table I), the 61 to 80 age class, with an average age of 
73 years, has only 6 per cent of the total trees infected, a9 
compared to 7 per cent on sites of the slope type for a similar 
age class with an average age of 65 years. Density of stand and in- 
juries such as fire scars could well be responsible for the increased 
infection of the trees on the slope sites. Farther along in the table it 
is found that for the bottom sites in the 81 to 100 age class, averag- 
ing 88 years, the percentage of infected trees is 37 as compared to 21 
for the slope sites with a similar age class, averaging 91 years. 
On both the slope and bottom types of site it is found that the 11 
to 60 age class is entirely free from visible infection; that is, no 
measurable rot recognizable to the naked eye was found in these 
trees. This fact alone would indicate that an age of earliest infec- 
tion placed at 50 years would be as nearly correct as the practical ap- 
plication of such an age demands. The site, apparently, is not the 
