, 1874-02-14
RELATIONS OF FORESTS TO
CLIMATE.
From the Galaxy.)

How the climate and health of a country
are affected by the removal of its forests, is a
question of peculiar interest to the people Of
the United States, and one also on which the
opinions of scientific men are widely divided.
Humboldt maintained that trees by the nature of
their exhalations, aud the radiation from their
leaves in a sky without clouds, surround
themselves with an atmosphere constantly cold
and misty. They influence the copiousness of
springs, not as many believe by a peculiar at
traction for the vapors ditfused through the
air, but because by sheltering the soil from the
direct action of the sun, they lessen the evapo-
tation of water produced by rain. They also
tend to equalize the volume Of rivers, by render
ing the rainfall more uniform, aud by imPed-
ing the flow of surface water into them. 1t
therefore happens that when forests are de-
stroyed, springs dry up or become less abundant,
rains are less frequent and more severe, and
floods and devastation are a not uncomm d
result. In India, the destruction of the forests
has been followed by a very marked change IN
the character of the climate. At Dapoolie the
climate is said to be much more hot and dry
than before the timber was cut down and
streams that then flowed until April or May
have since commonly dried up in December.
To Coucan a similar state of things resulted
from the destruction Of vegetation. The long
droughts now 50 frequent in the Cape Verd
Islands, and the iuc, eased amount OF disease
which accompanies them, are a~voWedIy due to
the removal of their forests. Ia the highlands
of Greece, where the timber has been cut a.
way, the springs are said to have disappeared.
During the day, trees not only shade the
ground, but by the escape Of yapOr from their
leaves mitigate the heat Of the atmosphere.
At night they radiate heat and condense the
vapor Of the air into the form Of dew, many
plants being endowed with this faculty to such
an extent as to collect water in large quanti-
ties from the atmosphere.
In a discussion on the subject Of climate and
the relation of forests thereto, which took
place a few years since in the British Associ-
alton, Capt Strachy contended in opposition
to the above views, that SO far from the forests
being the cause either Of the rainfall or lis fuc-
t~uatiOns, it was more probable that rain was
the cause Of forests. He inStanCed certain dis
tricts in India, where the forest vegetation was
Just in proportion to the fall Of rain, being
scarce, stuuted, and weakly where there was
little rain, and abundant, gigantic, and vigorous
where there was much rain. In temperate
climates forests might produce an effect, but
certainly not in the tropics Several districts
were named where forests did not exist, and
there was much rain and others where the for
ests were extensive and there was but little
rain. 1t was remarked by DR.. Lancaster in the
same discussion, that, according to the laws of
vegetation, plants must be supplied with water
in a liquid or vaporous form for their growth,
and that all the facts which had been mention
ed, and which at first sight appeared opposed
to each other, might be explained. That for
ests did not always grow in rainy districts arose
probably from the waters accommodating and
forming morasses, in which forest trees would
not grow. In districts where there was not
much rain, there might be a great deal fmois-