Dec. is, 1925 Yield Capacities of Yellow Pine Type in California 1127 
INDICATIONS OF THE DATA 
It will be seen, considering first the chart for board-foot volume 
(fig. 1), that the curves flatten off very decidedly at about 90 to 100 
years of age at breast height; in other words, that that age repre¬ 
sents the culmination of current annual increment. A little study of 
the other charts will perhaps explain why volume growth falls off at 
100 years. It is seen first (fig. 2) that basal area per acre also drops 
considerably at 100 years, and that height growth (figs. 3 and 4) 
culminates at that age, this curve especially showing a very sharp 
flattening. In diameter growth (fig. 5) and basal area growth of 
individual trees it is rather more difficult to say confidently that 100 
years represents the culmination. Both of these curves show a very 
gradual flattening and a study of them alone would probably be of 
little assistance in determining rotation. 
40 60 80 100 120 140 160 100 
AGE OF DOMINANTS AT BREAST HEIGHT 
' Fig. 1.—Yield per acre on age, board feet 
The curves in Figure 6 showing trees per acre are unusually inter¬ 
esting. The upper curve gives total number of trees 4 inches in 
diameter up, while the lower curve shows trees per acre of mer¬ 
chantable size; that is, 8 inches and over. The latter curve indicates 
a rapid increase in the number of these trees per acre up to 80 years, 
and then a more gradual decrease in number up to the highest age 
reached by these studies. In other words, what evidently takes place 
in nature is that stands at 80 to 100 years reach a period of develop¬ 
ment when suppression, and perhaps other factors, begin to reduce 
the number of trees 8 inches and over more rapidly than smaller 
trees grow into that class. These curves thus snow why and how 
volume growth begins to fall off after about 100 years age at breast 
height. Apparently height growth, total basal area growth, diameter 
growth, and number of trees per acre all tend to culminate at about 
