12 



BULLETIN 799, U. S. DEPAETMENT 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, ivith reference to the infection age 

 of western white pine on sites of the Tyottom 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- 

 age rot 



Total. 



In- 

 fected. 



Per- 

 centage 



in- 

 fected. 



Total. 



In- 

 fected. 



Per- 

 centage 



in- 

 fected. 



per m- 

 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, as 

 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 41 

 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 



