CHAPTER XXVI 

 GROWTH OF TREES IN VOLUME 



286. Relation between Volume Growth, Form and Diameter Growth. 



The growth of trees in volume is the product of the growth in height 

 and the growth in area at different portions of the stem, which is 

 expressed in diameter growth. The exact form of the tree and the rela- 

 tion between diameter and resulting area and volume growth at dif- 

 ferent heights from the ground are the result of mechanical laws of 

 resistance to stresses. The form of the tree is intended to resist wind 

 pressure in order to maintain its upright position and not be snapped 

 off or blown over. As was shown in Chapter XVI this pressure is 

 directly caused by the force of the winds acting on the crown and 

 focused in the center of area of the crown exposure (§172). Growth 

 in diameter will be distributed in response to this strain to give the 

 maximum resistance with the minimum of material. 



As the form of crown and its position with respect to the bole changes, 

 the point of average pressure shifts and the form of the tree will be 

 modified by a more rapid diameter growth at the points requiring 

 strengthening. An increase in the stress to which the tree is exposed 

 will also cause changes in the distribution of growth. Trees which 

 have grown in a protected stand and are exposed by cutting will either 

 blow over or will rapidly strengthen their resistance by laying on 

 increased growth at the base or stump where the effect of this change 

 in exposure is most evident. The upper form of the tree, being influ- 

 enced by crown, does not change appreciably. Trees in a leaning 

 position continually add most of the diameter growth on the under side. 



Where the growth in volume of a tree on cut-over areas is judged 

 from the growth in diameter on the stump, without correction, a rate 

 of from 50 to 100 per cent in excess of the true volume growth may be 

 obtained. Such measurements should therefore be taken at B.H. 

 where the effect of this increase is not felt, or else growth measurements 

 taken on the stump must be carefully compared with measurements 

 at upper points on the tree. 



287. Tree Analysis, its Purpose and Application. The analysis of 

 an individual tree by the measurement of diameter growth at upper 

 sections, in order to determine its volume growth, is termed tree analysis, 

 (synonym, stem analysis, § 254). This process enables one to determine 



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