344 



GROWTH OF TREES IN DIAMETER 



of these methods is based on the purpose of the study. In all measure- 

 ments of diameter growth, an average rate is to be found by combining 

 the growth of a large number of trees. This means averaging together 

 the growth by decades. The trees so averaged usually differ in age, 

 sometimes over a v/ide range. The growth of the last decade, or current 

 periodic growth on all trees, regardless of their total age, is represented 

 by the outside or last ten rings. Any influence, such as cutting, fire or 

 climate, which affects diameter growth, must be studied on the basis 

 of current growth. In making a tree analysis, which requires the growth 



Countinii 

 from 

 Center, 

 Years 



Fig. 68. — Alternate methods of counting and measuring annual rings on a cross 

 section 36 years old. On left, rings are counted in decades beginning with 

 outer ring. On right, count begins with center and odd rings fall on outside. 



in diameter of upper sections (§ 289) the separation of the growth in 

 volume for each past decade requires the measurement of the same 

 ten rings on each of the sections analyzed. This is secured by counting 

 back from the outer ring. When growth is studied for these purposes, 

 rings must always be counted from the outside inward. In this case 

 the first measurement from the pith outward will be the fractional 

 decade. The average growth for this period represents the average 

 number of years less than 10 which were measured. This may vary 

 from 1 to 9 years but tends to average 5 years. The second decade 

 will include, on different trees, the years 2 to 19, the third, 12 to 29; 



