HEIGHT INCREMENT. /9 



The determination of the increment may refer to the past 

 (backward), or to the future (forward). As the former deals 

 with actually existing quantities, the determination can be 

 made with a comparatively high degree of accuracy ; the latter, 

 on the other hand, is to a considerable extent based on specu- 

 lation, hence less reliable. 



Section I. — Detekmination of the Increment of 

 Single Trees. 



1. Height Increment, 

 a. Of the Past. 



The height increment of standing trees can, in some cases, 

 be ascertained by the whorls formed in successive years. This, 

 however, refers to a limited number of species. In the majority 

 of cases, it is necessary to cut down a tree for the purpose of 

 investigating the height increment. 



The height increment of the last few, say n, years can be 

 ascertained, in the case of some conifers, by measuring the 

 length of the last n shoots. In the case of all other species, 

 the height increment of the tree during the last n years is 

 ascertained by cutting off a certain length and counting the 

 rings ; if they are less than n in number, an additional piece 

 must be cut off and so on, until that spot has been found, 

 where the section shows n rings. If the section of the 

 first cut shows more than n rings, then another cut higher 

 up is made, until again the section shows n rings. The 

 length above that point gives the height growth of the 

 last n years. 



In all cases, where a complete knowledge of the height 

 increment during the several periods of life is required, the 

 tree should be divided into a number of sections, the length 

 of which depends on the desired degree of accuracy. The con- 

 centric rings are then counted at the end of each section, and, 

 from the data thus obtained, the height of the tree at successive 



