Second, by first raising young trees in nurseries and later setting them out in their permanent locations in the forest.  This method is applicable where quick results are desired, where the area is not too large, or in treeless regions and large open gaps where there is little chance for new trees to spring up from seed furnished by the neighboring trees.  It is a method extensively practiced abroad where some of the finest forests are the result.  The U.S. government, as well as many of the States, maintain forest-tree nurseries where millions of little trees are grown from seed and planted out on the National and State forests.  Fig. 129 shows men engaged in this work.  The fundamental principles of starting and maintaining a nursery have already been referred to in the chapter on “What Trees to Plant and How.”

The third method of establishing a forest from seed is by cutting the trees in the existing forest so that the seed falling from the remaining trees will, with the addition of light and space, readily take root and fill in the gaps with a vigorous growth of trees, without artificial seeding or planting.  This gives rise to several methods of cutting or harvesting forests for the purpose of encouraging natural reproduction.  The cutting may extend to single trees over the whole area or over only a part of the whole area.  Where the cutting is confined to single trees, the system is known as the “Selection System,” because the trees are selected individually, with a view to retaining the best and most vigorous stock and removing the overcrowding specimens and those that are fully mature or infested with disease or insects.

Fig. 130 is a diagrammatic illustration of the operation of this system.  In another system the cutting is done in groups, or in strips, and the number of areas of the groups or strips is extended from time to time until the whole forest is cleared.  This system is illustrated in Fig. 131.  Still another method consists in encouraging trees which will thrive in the shade, such as the beech, spruce and hemlock, to grow under light-demanding trees like the pine.  This system presents a “two-storied” forest and is known by that name.  The under story often has to be established by planting.

[Illustration:  FIG. 131.—­Diagrammatic Illustration of the Group or Strip System.]

In the system of reproducing forests from shoots or suckers, all trees of a certain species on a given area are cut off and the old stumps and roots are depended upon to produce a new set of sprouts, the strongest of which will later develop into trees.  The coniferous trees do not lend themselves at all to this system of treatment, and, among the broadleaf trees, the species vary in their ability to sprout.  Some, like the chestnut and poplar, sprout profusely; others sprout very little.

How forests are protected:  Forestry also tries to protect the forests
    from many destructive agencies.  Wasteful lumbering and fire are the
    worst enemies of the forest.  Fungi, insects, grazing, wind, snow and
    floods are the other enemies.