inches, or thirty-five in all which are over
6 inches. If the growth study indicates that in 20 years there will
have been added 6 inches in diameter we can estimate a crop of
five trees each of classes extending from 12 to 18 inches. Actually
the process will not be so simple, for the different aged trees
will not grow with equal rapidity, and several other factors must
be reckoned with, but the general principle is to apply rate of
growth knowledge to the material on hand, and study of this material
is essential.

For predicting even-aged crops resulting from entire restocking,
the acquisition of necessary basic information is as difficult, or
more so, but its application is far simpler. That the ground will
be fully stocked by natural or artificial means must be assumed,
but we can also assume that the result will be influenced only by
normal locality conditions and not by accidental condition of the
present forest. Therefore we use a yield table and not a growth
table. This can be made by actual measurement of existing second
growth stands of different ages, which proves not only the growth
rate but also the number of trees which the natural shade-thinning
process results in at different periods of the forest life. The
chief danger of inaccuracy in such information lies in basing it on
insufficient measurements or in applying it where soil or moisture
conditions are greatly different. The latter error can be guarded
against, however, by use of growth figures taken in conjunction
with it. For example, if a yield table showing 25,000 feet to the
acre at 50 years from seed is accompanied by one showing that the
average stand it represents is 125 high at 50 years and its average
50-year-tree is 14 inches in diameter, little investigation is
necessary to determine whether in any given locality the growth
falls far above or below that.

An attempt to reproduce here any considerable number of growth
and yield tables would be of doubtful use without more space than
is allowed to explain how they are made and used. There are many
technicalities, both mathematical and silvicultural, and unfortunately
most of the available figures for the Northwest, obtained by the
Forest Service, have not been generalized enough for wide popular
value. This is particularly true of yield tables which necessarily
require assuming standards of merchantability. While the best western
white pine table assumes that by the time a new crop is cut