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 dev