CHAPTER XXIV 

 GROWTH OF TREES IN DIAMETER 



264. Purposes of Studying Diameter Growth. One purpose of 

 studying the growth of trees in diameter is to determine the total volume 

 of trees of given ages, or the growth in volume of trees for a short period. 

 The volume of trees is based on D.B.H. and height. The diameter 

 growth must always be correlated with D.B.H. for the trees measured, 

 and height growth is usually required. A second purpose is to determine 

 the dimensions or sizes reached by trees in a given period. 



265. The Basis for Determining Diameter Growth for Trees. It 

 is impractical to cut sections at B.H. for growth measurements. Not 

 only is there a needless waste of timber, but the labor of felling and sec- 

 tioning the tree may also be avoided if the measurements are taken 

 at the stump following logging operations. Where current growth for 

 short periods is tested with an increment borer (§ 277) the measure- 

 ment is taken at D.B.H. The growth measurements on stumps require 

 three steps to determine the ages of trees of given D.B.H. outside the 

 bark; namely, 



1. Diameter growth on the stump. 



2. Correction for age of the seedling. 



3. Correlation between stump diameter inside bark and D.B.H. 



outside bark. 

 As diameter increases rapidly at the stump, the lower a stump is 

 cut the greater will be the apparent rate of growth for the tree. Stump 

 height classes differing by 6 inches may be made in growth studies, 

 but this is not often done. Stump heights usually vary with stump 

 diameters in a ratio of from one-third to two-thirds of the diameter, 

 depending on the closeness of utilization. For a given region and 

 standard, the stump heights for given diameters are fairly constant 

 and the average rate of growth is found for stumps of each diameter 

 with all stump heights averaged together. 



266. The Measurement of Diameter Growth on Sections. The 

 section measured must be at right angles with the axis of the bole. 

 In stumps this means a horizontal cross cut. Slanting cross cuts exag- 

 gerate the length of the radius and result in a slight plus error in growth 

 measurements. The procedure is as follows: 



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