﻿WHITE PINE UNDEK FOREST MANAGEMENT. 19 



Height growth is also influenced by the amount of light which the 

 tree receives. It is most rapid when the upper part of the crown alone 

 receives a fmll supply. In open-grown trees, which receive light from 

 all sides, the growth energy is distributed over many large branches, 

 and height growth culminates early, so that the tree remains rela- 

 tively short, stout, and branchy. On the other hand, if the trees 

 grow so closely together that the crowns arc small and crowded, the 

 rate of growth will again be slow. 



It is thus evident that trees of the same age and growing in the same 

 situations may vary somewhat in the rate of growth, according to 

 their nearness to one another. This difference, however, is much less 

 than that caused by a marked difference in the quality of the soil. 

 Height growth is, in fact, commonly considered the most reliable 

 single indication of site quality. 



Since ordinarily only one whorl of branches is produced in a single 

 year, the age of young to moderately old trees can usually be de- 

 termined roughly by counting the number of whorls or the scars left 

 by them. When these are absent close to the ground it is necessary to 

 estimate the period which the tree required to grow to the height of 

 the first visible whorl. For rough age determination it will usually do 

 to assume that it took 10 years to reach breast height. 



Growth in Diameter. 



Growth in diameter takes place through the formation of the thin, 

 concentric layers of wood, commonly called annual rings. With very 

 rare exceptions only a single ring is formed each year, so that the 

 number and width of the rings are a safe guide in determining the 

 age and rate of growth of the tree. To determine the precise age it 

 would be necessary to cut the tree at or within an inch of the surface 

 of the ground, since only in this way can the first year's growth be 

 included. Naturally, the further up the tree the section is cut, the 

 less will be the number of rings, and the amount of this difference is 

 the number of years it has taken the tree to reach the height of the 

 cross section. It is customary to express growth in terms of the 

 diameter breasthigh, since on standing trees this is the point at which 

 the diameter is usually measured. 



Like growth in height, the diameter growth of white pine reaches 

 its maximum early in life, and then slowly decreases. It is more per- 

 sistent than the height growth, however, and continues at a moderate 

 rate long after the former has practically ceased. Trees 60 or 70 

 years old may still be growing fairly rapidly in diameter. 



Diameter growth is slowest when the light supply is barely suf- 

 ficient to keep the tree alive, and most rapid when the tree grows 

 with its crown in full light and produces a heavy foliage. On dry 

 soils or where there is deficient air moisture diameter growth, like 

 height growth, is slow. This is true also of swampy soils. 



