SUBSTITUTING AVERAGE GROWTH IN FORM OR TAPERS 381 



of diameter growth, including the stump section, transfer or assemble 

 each of these curves on a single sheet whose zero represents the zero 

 year of the tree's age. 



In Fig. 81 the curve of stump growth from Table LIX is plotted 

 with the zero at 2 

 years, age of seed- 

 ling of stump height. 

 This is usually as- 

 sumed to be also 

 the origin of the 

 D.B.H. curve. For 

 the curve of diam- 

 eter growth at 8 feet, 

 the period required 

 to grow to this 

 height by Fig. 81, 

 or by interpolation 

 in Table LIX is 7 

 years plus 2 years 

 for seedling. The 

 zero is placed at 9 

 years. Since the 

 first fractional dec- 

 ade averaged 6 years 

 on these sections, the 

 first diameter is plot- 

 ted above 9+6 = 15 years, and subsequent decades at 25, 35 years, 

 etc., as indicated by the points. 



The height growth for section 3 at 16 feet took 15+2=17 years. 

 The first fractional decade was 6 years. The points are plotted above 

 23, 33, 43 years. In this way each upper section is plotted on the sheet 

 representing the age of the average tree. 1 



To read this record for the purpose of determining the volume in 

 any given unit for a tree of a given age, the dimensions of a tree of the 

 required age fall in the vertical line intersecting this age. For instance, 

 a tree 40 years old will have its diameter inside bark at the 16-foot 

 cross section indicated in Fig. 81 as 2.4 inches. Reading upwards 

 as the diameter increases, the next lower cross section has a diameter 

 of 3.4 inches and D.B.H. is 4.8 inches. Since the height or distance 

 between these cross sections cannot be shown on this diagram, but 



I 40 



Age, years 



60 



60 



Fig. 81.— Diameters at 8-foot points, for an average tree 

 at different ages, or growth analysis. Chestnut Oak, 

 Milford, Pike Co., Pa. 



1 In the above figure, D. B. H. outside bark exceeds D. I. B. at stump up to 

 about 7 inches. This frequently occurs on small thick-barked trees. 



