Most persons will have observed the effect
of heat radiation from rocks, or even from the walls of a building that
have been exposed to a summer's sun during the long day. At about six
P.M., when the air is cool, the sun-heat stored by absorption escapes
from its imprisonment, and thermometers would exhibit a difference of
many degrees if placed at two feet from the ground, and at fifty; the
rocks and earth have been heated like an oven. Trees will affect the
surface of the soil in the same manner that an umbrella protects an
individual from the surf, and upon lofty mountains they exercise a
marked influence upon the rainfall. Should the summits be naked, the
rocks become heated to a high degree, and should clouds pass overhead,
the vapour would not condense, but, on the contrary, it might disperse
upon contact with the heated surface. If the summits were clothed with
forests, the rocks and soil, being shaded from the sun, would remain
cool, and the low temperature of earth and foliage would condense the
vapour and produce rain. It is well known that trees exert a direct
influence upon meteorological phenomena, therefore should forests be
totally destroyed, a change may be expected in the temperature, attended
by a corresponding decrease in the rainfall. It is obvious that should a
country be entirely covered with trees and jungle, it will be too damp
and unhealthy for the occupation of man; and should it be absolutely
barren of forest, it will possess a minimum rainfall; therefore in all
countries that are expected to develop agricultural resources, the due
proportions of woods and forests require special attention.
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