, 1875-01-16
MORE ABOUT THE INFLUENCE OF
FORESTS ON CLIMATE.


From tie CouaLy Geat1cman's Uaga73pe)
-O-
have yet to learn that any government OF scjenti-
fc body has ever taken up in a right way those points
in the scientific Culture Of trees, the calculations Of
which is SO much wanted to Guide and assist landed
proprietors and pract. cal f rosters: or those influences,
good or bad, which trees are found to possess over
the soil and climate, and hence over the health Of
other vegetation, as we'll as that Of animals.
To the superficial observer there has not perhaps
been occasion for any particular notice Of a science
which many consider as merely a branch of agricul-
ture, and who probably see no cause TO give arboricuI-
ture an independent standing. | wish then to re.
move this objection, and to claim for arborjculture
that position which | hope to shew its importance
eminenty deserves, and urgently demands.
What is Arboricu)ture? To the practical forester
it is the production of the best timber at the least
cost, in The largest quantity and shortest time. TO
plant, thin, and clear, for profit, Is almost his sole
object. The value Of woods is vet estimated very
much by the amount of their own produce. Such a
view OF them renlnd5 me Of q proprietor who holds
ordinary stock in It railway through his lands, and
who expects good DIVIDENDS besides the many indirect
advantages Of the Increased communication. One so
c5rcunSa1ced would be selfish and unrea sonabie did
he expect FIVE per cent. for his money and SO. those
who are dissatisfied with 20 or 25 per acre per
anDUn [oH averages Of soil aud kinds OF trees) from
their wood crops. without reference to climate and
health, are equally selfish and unreasonable. ! pur-
pose then 10 slew the value 0. trees in conneXion
with climate and health.
a treo. Z. fa IFS branches and leaves, is bunch Of
iub8linr and ez1AIinr organisms. Evaporation and
limitation q en- from the tin leaves, as they are
heated by TIE suns rays, or cooled at night, IN tho
same manner as other bodies. BgCh9n says that
trees may be conceived as reservoirs in which the
heat Of the day is stored up against the cod Of the
night.
"Tho effect then eff trees on The temperature is to
make tho nights warmer and the days cooler and
from this it follows that they diminish the summer
temperature and maintain that OF winter higher than
it would otherwise be. This enables us to understand
how ,rees Increase the rainfall for suppose a forest
to lower the summer heat Of district 10 the extent
of about %. the effect on the rain-bringing winds
would be much the same as if a low range of hills
opposed their course, and condensed their yapour into
rain"
The influences Of trees are ascertaincd in two
WAYS, viz. in the diminished raji alton from the sur
face protected by trees, and in the obstacles they OPP
pose to the descending currents OF cold air. Hum
boldt saws that trees &" cXhale fluid from their leaves,
in the first place. for their own benefit. But various
important secondary effects follow from this process
One of them is, maintaining a suitable portion Of
humidity in the air. Not only do they attract and
condeuse the moisture suspended in the air, and
borne by the wind over the earth's surface, which,
falling from their leaves, keeps the ground below
moist and cool, but they can, by means of their
roots, pump it up from 4 very considerable depth,
and, raising it into the atmosphere, dItfuse it over
the face Of the country. Trees by the perspiration
from their leaves, surround themselves with an at
m~osphere constantly cool and moist. They also
shelter thesoil from the direct action of the sun, and
thus prevent evaporation of the water furnished by
rains.''
Such, briefly, are the breathing or p~erspiring eff
fects of trees upon the atmosphere. There is no
want of proof of these effects, and I shall give a few
examples, At the Cape of Good Hope, Sir John
Herscbel observed on the side of Table Mountain,
from which the wind blow, the clouds spread out, and
descend very low, frequently without any rain falling
while on the opposite side they covered the mountain
in dense masses of vapour. When walking beneath
tall fr-trees at the time those clouds were closely over
laid he was subjected to a heavy shower of rain, but
on going out from beneath the trees, the rain ceased