MEASUREMENT OF HEIGHT GROWTH 



371 



TABLE LVII 



Height Growth of Chestnut Oak, Milford, Pike Co., Pa. 



Basis, Ten Trees 



The total height, based on total age, of these ten trees is shown by the last ten 

 points. It is evident that with a sufficient number of trees of all ages, a height curve 

 based on age could be constructed without analyzing the trees above the stump sec- 

 tion, but it is equally evident that such analyses, as shown in the figure, not only 

 multiply the weight of each tree by the number of sections taken but substitute 

 actual growth of given trees for composite growth by comparison of different trees. 

 Such a history or record of growth, whether it is of diameter, height or yields per acre, 

 (§ 266 and § 326), is the most reliable basis of growth data. 



Current Height Growth. The current or periodic height growth 

 for the last decade or two may be required to complete the data for 

 determining the current volume growth of trees. This should be meas- 

 ured on felled trees by cutting back the tip until a section is found 

 containing the required number of rings. For determining growth 

 for short periods this is a simple process. Only on young trees should 

 the last period of growth be determined by counting back the number 

 of whorls from the tip In older timber and especially on standing 

 trees, it is impossible to secure accuracy by this method. 



285. The Substitution of Curves of Average Height Based on 

 Diameter for Actual Measurement of Height Growth. In studies 

 intended to determine the volume growth of trees, especially of seed 

 trees and young timber left on cut-over lands, a method has been sought 



data are identical with the original figures, the advantage lying in the graphic classi- 

 fication of the data for averaging. But for the next and subsequent decades the base, 

 for age, can be shifted to the right by one decade, so that the points " over " include 

 only the fractional decade, while for height the base can be raised to exclude that 

 portion of the graph which includes no points. Thus, for the third decade there are 



9 points, whose weights vary from 1 to 10 years or points. For age, the basis or 

 zero is 20 years and the points " over " are 1, 2, 3, 6, 6, 7, 8, 9 and 10, or a total of 

 52, average 5.8 points " over " or 25.8 years. For height the base may be taken at 



10 feet and the points " up " are then 6, 14, 14, 14, 22, 22, 22, 22, 30, a total of 166 

 points " up," average 18.4 points up, or 28.4 feet. In plotting, where two or more 

 dots fall on the same point, a numeral must be written in, as indicated, to show the 

 weight of the point. 



