has established timber preserves in several
localities in the West. The State of New York has converted the whole
Adirondack region into a great preserve. Forest wardens and guards are
employed both to keep fires in check and to prevent the ravages of
timber thieves; excepting the State preserves however, the means of
prevention are inadequate for either purpose.

[Illustration: THE LUMBER INDUSTRY--A LOG JAM]

To be valuable for lumber of the best quality, a forest tree must be
"clear"; that is, it must be free from knots at least fifteen feet from
the ground. In the case of pines and cedars, the clear part of the trunk
must have a greater length. To produce such conditions, the trees must
grow thickly together, in order that the lower branches may not mature.

The growth of trees thus set is very slow. Isolated pine-trees will
reach the size large enough for cutting in about fifty years, but the
lumber will be practically worthless because of the knots. On the other
hand, pine forests with the trees so thickly set as to make a clear,
merchantable lumber require at least a century for maturity.[49] Oak
forests require a much greater period.

As a rule, the forest growths of the United States are found in the
areas characterized by sandy and gravelly soils. Thus, the glaciated
region of the United States and Canada for the greater part is
forest-covered. The sand barrens along the Atlantic coast usually are
forest areas. The older bottom-lands of most rivers are often
forest-covered, especially when their soil is coarse and sandy.

There are large areas, however, in both the United States and Europe,
that are treeless. In some instances this condition, without doubt,
resulted from the fires that annually burnt the grass. With the
cessation of the prairie fires, forest growths have steadily increased.

In other instances these areas are treeless because the seeds of trees
have never been planted there. The high plains at the eastern base of
the Rocky Mountains are an example. This region is deficient in the
moisture required to give young trees the vigorous start that will
carry them to maturity. Moreover, the westerly winds and the streams of
this region come from localities also deficient in forestry, and there
are therefore no seeds to be carried.

As a rule, the distribution of forests is effected by the winds and by
moving water. The prevailing westerly winds of the temperate zones have
carried many species e