﻿20 BULLETIN 13, U. S. DEPARTMENT OP AGRICULTURE. 



Growth in Volume. 



Growth in volume is the product of growth in both ,height and 

 diameter, and is influenced, moreover, by the shape of the tree. In 

 white pine its rate becomes rapid after the period of rapid height 

 growth has passed, and persists to an advanced age, gradually becom- 

 ing less, until in old age it is more than offset by decay. Like that 

 of diameter growth, the rate is more rapid in the case of open-grown 

 trees with large crowns than in forest trees with small crowns, 

 though, as previously mentioned, the wood produced is less valuable. 

 . Along with the growth in volume there proceeds an increase in 

 quality. This takes place partly through the mere increase in the 

 size of the lumber which can be sawed out and partly through the 

 increase in freedom from knots. White pine holds its branches so 

 tenaciously, however, that, unless pruned, little freedom from knots 

 can be expected before the fiftieth year. The quality of the timber is 

 further improved by the conversion of the soft sapwood into heart- 

 wood, which goes on somewhat irregularly as the diameter increases. 



GROWTH OF STANDS. 



The development of a white-pine stand is a continued struggle 

 between the trees for light and growing space. This struggle com- 

 mences when the branch tips of the seedlings begin to touch and 

 interfere with each other, and is most acute during the early period 

 of rapid height growth. Success of individual trees in the competi- 

 tion is determined by their ability to make rapid height growth, 

 and so to keep their crowns in the light. As the less vigorous trees 

 fall behind, they become more and more shaded by their thriftier 

 neighbors, and finally die. The mortality from crown competition 

 gradually decreases from the early period of vigorous growth, until 

 at the time the trees have reached full size it is very small. The 

 decrease in the number of trees, however, is more than made up by 

 the size of the survivors. This is shown in Tables 3 to 5, where, even 

 when the decrease in the number of trees is most rapid, the aggre- 

 gate basal area, breast high, and volume per acre continue to in- 

 crease — rapidly in first-quality and slowly in third-quality stands. 



The difference in height and crown vigor which this struggle 

 brings about makes it possible to classify the trees of a stand in the 

 following way: (1) dominant trees, which have full and vigorous 

 crowns and in general overtop their neighbors; (2) codominant, 

 those with narrower crowns, which are beginning to fall behind the 

 dominant trees in height growth; (3) intermediate, shorter trees, 

 closely crowded by their neighbors and receiving light only from 

 above; (4) suppressed trees, those which are shaded from above as 

 well as from the sides, and which will soon die ; (5) dead, trees which 

 have finally succumbed to shade. 



