addition of 5 feet,
a year throughout its life. If at 125 years old it contains but
560 feet, the average increment will be but 4-1/2 feet a year.
It will not give equal return for the soil, moisture and light
it monopolizes during these 25 years. At the same time, probably
there are young trees nearby which hitherto have averaged below
the maximum, but if released from its competition will forge ahead
for a period at the end of which they will give a greater annual
return than if cut at present. It would be as bad economy to cut
these today as to spare the over-mature tree. In short, the production
of the forest is not only sustained, but actually increased, by
removing the oldest trees at just the proper time; and is decreased
by taking out young trees either not yet at the natural age of
greatest mean annual increment or capable of artificial stimulation
by thinning.

By studying the relation of age to production in the particular
locality, the proportion of different age classes, and also finding
the approximate average diameter which corresponds to the age at
which he desires to cut, the professional forester can make a very
accurate selection of the trees which can be removed to best advantage
at present and also fix the time and yield of the next cutting.
Fortunately, however, commercial and silvicultural considerations
accidentally coincide so nearly under average yellow pine conditions
as to make certain rough rules which can be laid down entirely
consistent with logging methods now in practice. Diameter is far
from exact indication of age, for the location of the forest and
the situation of the individual tree, especially as it affects the
relation between height and diameter growth, are potent factors,
but as a rule merchantability for saw-material is not far from
maturity.

In a great majority of cases the approximate minimum diameter for
cutting which would be fixed by it forester would be somewhere
between 16 and 30 inches, but say it were 18 inches, for example,
it would not arbitrarily apply throughout the stand. Most trees with
yellow, smooth bark and small heavy-limbed tops, perhaps partially
dead, are mature regardless of their size. If small, they have
been crowded or stunted and may as well be cut. Trees with large,
healthy crowns composed of many comparatively small branches, and
with rough dark bark showing no flat scaling, are sure to be growing
rapidly, even if quite large. They are also les