20 BULLETIN 13, U. S. DEPARTMENT OF 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 hi 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 hi 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 hi height and crown vigor which this struggle 
brings about makes it possible to classify the trees of a stand in the 
folio whig way: (1) dominant trees, which have full and vigorous 
crowns and hi 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. 
