46 



Forest Mensuration 



has required to grow through the distance lying between these two sec- 

 tions. By counting the number of rings at several cross sections, one of 

 which is made as close to the ground as possible, the current and the 

 average height growth (increment) may be obtained by arithmetical or 

 by graphical interpolation. 



A dense cover favors height increment. In rare instances, however, 

 the stand of saplings or poles is so close that the height increment of 

 the individual suffers from lack of food. 



PARAGRAPH LXXIV. 



THE CURRENT HEIGHT INCREMENT. 



In the high forest the current annual height increment reaches a 

 maximum at an early age; passing this maximum, it sinks more or less 

 rapidly. The culmination of the current annual height increment occurs 

 the much earlier and its slackening after said culmination goes on at a 

 more rapid rate if 



1. the species is fast growing and light demanding; 



2. the tree observed belongs to the dominant class ; 



3. the soil is good. 



For yellow pine the culmination of the current annual height incre- 

 ment occurs amongst dominant saplings between the loth and isth years; 

 for spruce at about the 2Oth year; for beech and fir between the 25th 

 and 3Oth years. Suppressed trees show the maximum of current height 

 growth much later than dominant trees. 



As a general rule for all species, in case of dominant trees, the longest 

 shoot is made 10 to 15 feet above ground. Slow growing species, shade 

 bearers and trees stocking on poor soil reach that level at a later date 

 than trees and species growing under reversed conditions. 



In the case of coppice forest, the maximum of the current height 

 growth lies in the first three years of the life of the shoot. For oak 

 coppice, the following table may serve as an illustration of height growth : 



GROWTH IN FEET. 



PARAGRAPH LXXV. 



THE AVERAGE HEIGHT INCREMENT. 



The average annual height increment culminates later than the current 

 annual height increment, and, after the culmination, it decreases at a less 



