made through the forest area to furnish protection against top fires.  Carefully managed forests are also patrolled during the dry season so that fires may be detected and attacked in their first stages.  Look-out stations, watch-towers, telephone-connections and signal stations are other means frequently resorted to for fire protection and control.  Notices warning campers and trespassers against starting fires are commonly posted in such forests. (Fig. 143.)

[Illustration:  FIG. 134.—­Sheep Grazing on Holy Cross National Forest, Colorado.  The drove consists of 1600 sheep, of which only part are shown in the photograph.]

The grazing of sheep, goats and cattle in the forest is another important source of injury to which foresters must give attention.  In the West this is quite a problem, for, when many thousands of these animals pass through a forest (Fig. 134), there is often very 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 trees, after they have been felled, must be cut and piled in heaps, as shown in Fig. 122, to prevent fire.  When the trunks, sawed into logs, are dragged through the woods, care is taken not to break down the young trees or to injure the bark of standing trees.  Waste in the