The Earth as Modified by Human ActionMarsh, George P. (George Perkins)
History
The Earth as Modified by Human Action
Marsh, George P. (George Perkins)
Conservation of natural resources; Human geography; Nature -- Effect of human beings on; Physical geography
The insects most injurious to the rural industry of the garden and the
ploughland do not multiply in or near the woods. The locust, which
ravages the East with its voracious armies, is bred in vast open plains
which admit the full heat of the sun to hasten the hatching of the eggs,
gather no moisture to destroy them, and harbor no bird to feed upon
thelarvae. [Footnote: Smela, in the government of Kiew, has, for some
years, not suffered at all from the locusts, which formerly came every
year in vast swarms, and the curculio, so injurious to the turnip crops,
is less destructive there than in other parts of the province. This
improvement is owing partly to the more thorough cultivation of the
soil, partly to the groves which are interspersed among the ploughlands.
... When in the midst of the plains woods shall be planted and filled
with insectivorous birds, the locusts will cease to be a plague and a
terror to the farmer.--Rentzsch, Der Wald, pp. 45, 46.] It is only since
the felling of the forests of Asia Minor and Cyrene that the locust has
become so fearfully destructive in those countries; and the grasshopper,
which now threatens to be almost as great a pest to the agriculture of
some North American soils, breeds in seriously injurious numbers only
where a wide extent of surface is bare of woods.
General Functions of Forests.
In the preceding pages we have seen that the electrical and chemical
action of the forest, though obscure, exercises probably a beneficial,
certainly not an injurious, influence on the composition and condition
of the atmosphere; that it serves as a protection against the diffusion
of miasmatic exhalations and malarious poisons; that it performs a most
important function as a mechanical shelter from blasting winds to
grounds and crops in the lee of it; that, as a conductor of heat, it
tends to equalize the temperature of the earth and the air; that its
dead products form a mantle over the surface, which protects the earth
from excessive heat and cold; that the evaporation from the leaves of
living trees, while it cools the air around them, diffuses through the
atmosphere a medium which resists the escape of warmth from the earth by
radiation, and hence that its general effect is to equilibrate caloric
influences and moderate extremes of temperature.
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