A STUDY OF HEART-EOT IN WESTERN HEMLOCK. 



17 



Table I represents all the trees of the 41 to 62 age class, inclusive, 

 taken from plats classed in the river-bottom and southwestern-slope 

 types. The 15 and 9 youngest trees of each site (river bottom and 

 southwestern slope) , respectively, were used to secure an average age 

 representing the infection age. This age for each tree was secured 

 by means of the formula, Ai=A— (Vh-Vi), where A^ equals age 

 of first infection, A equals age of tree, V equals volume of rot of 

 the tree, and V^ equals the average annual increase in rot volume 

 for the age class in which the tree is included. This last figure is 

 obtained from Table II. It was attempted to use the first 15 trees 

 of the southwestern-slope type. This gave an infection age of 70 

 years but included trees as old as 99 years, while the oldest tree 

 of the river-bottom type was only 62 years. In using 9 trees, the 

 oldest tree of the slope site is 75 years, giving a more equal 

 comparison. 



Table I. — Data relating to the infection age of heart-rot in western hemlock on plats of 

 the river-bottom and southwestern-slope types. 



River-bottom type: 2 



46 yearS 



48 years 



54 years . ; 



54 years 



55 years 



55 years 



56 years 



57 years 



57 years 



58 years 



60 years 



61 years 



62 years 



62 years 



62 years 



Average . 



Slope type: s 

 54 years . . 

 57 years . . 

 60 years . . 

 62 years . . 

 67 years . . 

 70 years . . 

 72 years . . 

 75 years . . 

 75 years . . 



Tree 



No. 



Volume of 

 rot. 



0.07 

 .03 

 .06 



.36 



.27 



.19 



.44 







.59 



1.11 



1.13 



.12 



Approxi- 

 mate value 

 forV-^Vi. 



Years. 



Probable 



age of 

 infection.i 



Years. 

 44 

 47 

 52 

 35 

 46 





 46 

 49 

 52 

 45 





 44 

 30 

 30 

 59 



Number of 



infected 

 trees(basis). 



1 Formula: Ai=A— (V-^Vi). Vi=0.035. 



2 Site description. — River-bottom flat, very moist; soil not well drained; stand very dense. Almost 

 all individuals of the tolerant species, such as western hemlock and grand fir, were overtopped or suppressed. 



3 Site description. — Southwestern slope, partly flat; old-age class of a white-pine type in which the 

 hemlock has become a eUmax species; soil fairly moist and well drained; stand not overcrowded. 



Table I shows that the average infection age for the river-bottom 

 type is 44.5 years and for the southwestern-slope type 57.3 years. 

 It thus appears from a comparison of the results shown in this table 

 63424°— 18— Bull. 722 3 



