A STUDY OF HEART-ROT IN WESTERN HEMLOCK. 15 



here used allowed for such rot as was to be found outside of a straight 

 line drawn from points on the rot sections appearing at both ends of 

 the logs and such rot as was found extending outward from the heart- 

 wood along the branch whorls. The advance rot is included in the 

 total rot in every case. The rot percentage was secured from the 

 two given volumes. 



The basis for classifying the seriousness of injury is given as follows: 



= No injuries. 



X = 1 to 4 branch stubs, no frost cracks, and very few miscellaneous injuries 

 (less than 2). 

 XX ^ 5 to 9 branch stubs, one frost crack, and a superficial blaze, logging scar, 

 or other slight injury. 

 XXX = 10 to 15 branch stubs, not more than 2 frost cracks, deep blazes, logging 

 scars or fire scars, and slight lightning injury, 

 xxxx = 15 or more branch stubs, more than 2 frost cracks, and heavy injuries 

 (injured and broken top, severe lightning, and other injuries). 



The grouping of trees according to the crown class has, in general 

 forestry practice, been almost entirely done by ocular estimate. In 

 the present study the four gradations of the crown class were taken 

 from Forest Service Bulletin 61^ and were used with the crown size 

 in composing the standard for crown rating. The actual size of the 

 crown and the crown class are used to determine this rating. The 

 crown sizes in square feet (length by width of crown) for each age 

 class are grouped together, the largest and smallest sizes compose the 

 extremes of the large and the very small crown divisions, respectively, 

 the remainder ranging in order of size between these two. The 

 group is then divided into four equal classes: Large, average, small, 

 and very small. The individual trees are then given their respective 

 crown rating according to the following outline : 



(1) Crown size, large. (Crown class 1.) 



(2) Crown size, average. (Crown class 2.) 



(3) Crown size, small or one sided. (Crown class 3.) 



(4) Crown size, very small. (Crown class 4.) 



The vigor of a tree is indicated by the size and condition of its 

 crown and by the f avorableness or unf avorableness of the position it 

 occupies, as well as by the narrowness of the sap zone and the fineness 

 of its annual rings. The injuries which the tree receives during the 

 course of its development also play an important part in influencing 

 its vigor. The rating for vigor has therefore been based upon the 

 following three factors, in the order of their importance: (1) Width 

 of average ring in sap, (2) crown rating, and (3) the degree of injury. 

 This rating for vigor at least comes nearer registering the true condi- 

 tion than a mere ocular estimate. The fixing of the standard or 

 average width (as in oo where the width is 0.12 to 0.19 inches) Was 



I Terms used in forestry and logging. U. S. Dept. Agr., Bur. Forestry Bui. 61, 53 p. 1905. 



