little young growth left and the future reproduction of the forest
is severely retarded. Grazing on our National Forests is regulated
by the Government.

As a means of protection against insects and fungi, all trees
infested are removed as soon as observed and in advance of all
others, whenever a lumbering operation is undertaken.

[Illustration: FIG. 135.--A Typical Montana Sawmill.]

How forests are harvested: Forestry and forest preservation require that
a forest should be cut and not merely held untouched. But it also
demands that the cutting shall be done on scientific principles, and
that only as much timber shall be removed in a given time as the
forest can produce in a corresponding period. After the cutting, the
forest must be left in a condition to produce another crop of
timber within a reasonable time: see Fig. 122. These fundamental
requirements represent the difference between conservative lumbering
and ordinary lumbering. Besides insuring a future supply of timber,
conservative lumbering, or lumbering on forestry principles, also
tends to preserve the forest floor and the young trees growing on
it, and to prevent injury to the remaining trees through fire,
insects and disease. It provides for a working plan by which the
kind, number and location of the trees to be cut are specified, the
height of the stumps is stipulated and the utilization of the wood
and by-products is regulated.

Conservative lumbering provides that the trees shall be cut as near
to the ground as possible and that they shall be felled with the
least damage to the young trees growing near by. The branches of the