The Forest Republican. [volume] (Tionesta, Pa.) 1869-1952, 1882-09-20
How Trees Influence Rainfall and
Climates.


In general way there begins TO be
spreading popular belief that forests
increase the rainfall of the country. As
to how this is done, however, no very
definite idea prevails. Scientific men
have been recently making some very
interesting experiments in this field.
The results show strongly that forests
do exercise decided favorable infu-
ence on climate and the water supply.
1t is not conclusively established that
they directly cause heavy rains. They
do, however, according to the best light
at the present to be had, increase the
frequency of light showers, and thus
are of incalculable benefit to vegetation.
In other ways the benefcent effect of
trees on climate, crops and fruits is
sufficiently we'll established. DR.. J. NJ,
Anders gives in the American Natural
list good summing up of the latest re
search on this subject. Not the least of
the benefits he M antions is the good
service belts of woodland do in protect.
ing vegetation from storms and icy
winds. 1t is very common now for en-
lightened farmers in the West and
Northwest to plant dense rows of trees
and hedges of evergreen along the
northern line OF their orchards and
grounds. DR.. Anders says:
"The experiment has been tried ex-
tensively in France of planting trees in
belts one hundred meters apart, and
with marked benefit to the climate, and
there are some good reasons for believ-
ing that a similar experiment in various
places in our own country would prove
equally advantageous. 1t has been OBJ
served many times that fruit grown in
the city surpasses in quality and size
that grown in the country, and this is
ascribable to the more effectual shelter
in the former place"
Forests influence the atmosphere
more powerfully by their effect on its
general humidity than in any other way.
| An evaporation of moisture from both
earth and trees takes place constantly.
The evaporation is greater from open
soil than from woodland, but the differ
ence is far more than made up by what
is called Transportation" of leaves of the
trees. This corresponds in degree to
the insensible perspiration of animals,
Some conclusive experiments were
made with growing pot plsnts, going to
show that leaves do not absorb mois-
ture, but that on the contrary, they
give it out. Moisture is absorbed
through the roots.
The quantity of insensible vapor that
is given off through leaves amount to
one and quarter ounce to the square
foot of leaf surface. The world old
metaphor of counting the leaves of the
trees has new significance in the light
of science. Pains taking experiment has
enabled those studying the matter to
make an approximate estimate of the
comparative amounts of vapor given off
by earth surface and leaf surface. They
have calculated that a square foot OF
soil sets free about six times as much
moisture as a square foot of leaf. The
leaf surface is, however, many times
greater than the soil surface-twelve
times greater, the scientists put it-so
that twice as much evaporation takes
place from forest as from open land.
When the wood of the country is cut
away, therefore other things being
equal, two thirds of the moisture giving
material of the atmosphere is gone with
it, Hence the long and fearful drought
on lands hare of trees. The Naturalist
writer says:
"From the data obtained it would
seem safe to infer that when the per-
centage of woodland is fair (25 to sc
per cent at least twelve inches of water
is transpired in the course of a season
in mild or temperate climates; or, in
other words, twelve inches of the tota
annual terrestrial evaporation. All this
vast amount of water is transpired in
about six months, or during the vegeta
tive period. Under these circumstances
an equivalent of nearly half the rain
fall during the warm season may be ao
counted for by the Transportation.
Another noteworthy fact too is tha
even during long continued droughts
when brooks and ponds have dried mp
this life bringing exhalation from the
trees continues constant. Our write
continues
''Moist air during winter tends Il
moderate extreme cold; during the sum
meT, on the contrary, it tends to COO
fba drouOhko. hanoa fONaaka Inv mOiafan