MEASUREMENT OF HEIGHT GROWTH 



369 



section. The number of rings shown by the section, when subtracted 

 from the total age of the tree (age of stump plus seedling age) gives 

 the years required to grow to this height. The process as shown in 

 Fig. 77 consists of the following steps: 



1. Determine age of tree from stump plus seedling age (§ 257). 



2. Count the rings at each successive upper section, and measure 



length of section to get height from ground. Include 

 height of stump. 



A 

 10 % 



10SS 



10g 



10 



20 



30 40 



Age, Years 



50 



60 



70 



80 



Fig. 78. — Alternate methods of averaging the heights of trees, for a curve of height 



based on age. Original data plotted. For curve ® average age 



at fixed heights is found. For curve © average height for each decade. 



The prolonged curve is made necessary by dropping out of fast-growing 



trees from the average by decades. 



3. Subtract these counts successively from total age of tree, to 



obtain total height growth at each section and age. 



4. Subtract the age of any section from that of the one below, 



to find the period required for the current growth in 

 height for the length of section. 



This method may be simplified by first computing the height growth 

 curve for the portion above the stump, on all trees, and afterwards 

 making the average correction required for stump height and correspond- 

 ing age of seedling, on the final curve or table. 



