26 



BULLETIN 1060, U. S. DEPARTMENT OF AGRICULTURE. 



Table 7.— Average diameter outside bark at 15 feet above ground at various 

 ages and average annual diameter grotvth in each decade of Sitlca spruce 

 groioing on all sites in Oregon and Washington. 



[Based on measurement 



of 557 dominant trees.] 



(Curved.) 



Age. 



Average 

 diameter. 



Average 

 annual 



diameter 

 growth 

 in each 

 decade. 



Age. 



Average 

 diameter. 



Average 

 annual 

 diameter 

 growth 

 in each 

 decade. 



Years. 

 20 



Inches. 

 2.0 

 5.6 

 9.5 

 12.8 

 15.7 

 18.2 

 20.5 

 22.5 

 24.4 

 26.3 

 28.1 

 29.9 

 31.5 

 33.1 

 34.7 

 36.2 

 37.7 

 39.2 

 40.6 

 42.0 



Inches. 



Years. 

 220 



Inches. 

 43.4 

 44.8 

 46.2 

 47.5 

 48.8 

 50.1 

 51.4 

 52.7 

 54.0 

 55.3 

 56.6 

 57.8 

 59.0 

 60.2 

 61.4 

 62.5 

 63.6 

 64.7 

 65.8 



Inches. 

 0.14 



30 







36 

 39 

 33 

 29 

 25 

 23 

 20 

 19 

 19 

 18 

 18 

 16 

 16 

 16 

 15 

 15 

 15 

 14 

 14 



230 



.14 



40 



240 



.14 



50 



250 



.13 



60 



260 



.13 



70 



270 



.13 



80 



280 



.13 



90 



290 



.13 



100 



300 



.13 



110 



310 



.13 



120 



320 



.13 



130 



330 



.12 



140 



340 



.12 



150 



350 



.12 



160 



360 



.12 



170 



370 



.11 



180 



380 



.11 



190 



390 



.11 



200 



400 



.11 



210 















Diameter measurements at breast height are of little value in a 

 Sitka spruce growth study, as this species commonly has a pro- 

 nounced basal swell and its root base is usually well above the gen- 

 eral ground level, owing to its habit of starting on down logs. For 

 these reasons, in Forest Service timber survey work in spruce, diam- 

 eters are taken at a point 1 foot above the swell ; but this is a variable 

 height and can not be used in growth studies when the relation be- 

 tween age and diameter is desired. In Table 7, therefore, diameters 

 are given for a distance 15 feet above the ground and on most trees 

 this point is above the basal swell. It must be borne in mind, how- 

 ever, that this uniform height above ground does not mean a uniform 

 distance between this point and the root bases of all the trees meas- 

 ured. Trees which started on fallen logs 4 or 5 feet in diameter 

 naturally have their root bases 4 or 5 feet above the ground, and the 

 number of annual rings showing at the 15-foot point in these trees 

 is, of course, less than at this point on trees whose root bases rest 

 on the ground. It was found, however, that the discrepancy for all 

 the trees measured amounted to only two years. This variation is 

 rendered of little consequence by the rapid height growth of Sitka 

 spruce in its sapling stage, when 3 feet per year is not an unusual 

 growth. Another point that must be kept in mind in this connec- 

 tion is that it takes an average of 14 years for the seedling to reach 

 a height of 15 feet, as shown by Table 5, and therefore a tree must 

 be more than 14 years old before it shows diameter at this point of 

 measurement. 



