The Hawaiian star. [volume] (Honolulu [Oahu]) 1893-1912, 1893-09-05
DO FORESTS INCREASE RAIN
FALL?

The recent decrease OF the rainfall
in a district OF one of the other islands,
and the remedy applied thereto, gives
local interest to this editorial of New
York paper, which the STAR is asked
to repubIish:
Accepting the conclusion that, in
general, fore SITS Increase slightly the
fall If rain, snow and dew, it remairs
to be determined how much If this
increase is available for beneficial pur-
poses. Part of 1t is intercepted by
foliage and is returned to the atmoS-
phere by evaporation without having
reached the ground. The proportion
so retained varies with the nature Of
the foliage, the density OF the fore st and
the season Of the year. The retention
by evergreen trees is less than by decid-
4ous 1t is estimated that perhaps 80
per cent of the precl pltatlon is thus
Intercepted and returned to the atmos-
phere. Of course this interrogation
md evaporation 60 on where the sur
lace OF the earth is covered by grass
and other growing crops. Whether II
is sufficiently greater Il. the forest than
in the fields to do away with the excess
| Of precipitation on wooded tracts over
that on cleared areas is an unsettled
question. The retention of snow by
foliage amounts to less than that of
rain, for most of the snow caught by
the leaves is shaken to the ground by
wind.
OF the 10 per cent. Of rainfall which,
1t is estimated, reaches the ground in
forests, part is very quickly returned
to the atmosphere by evaporation, but
+ here the loss is considerably less than
IN the open field. Under certain con-
ditions it is not more than 8 per cent.
Of what it would be on bare soil but
the conditions are SO various that it is
difficult to arrive at an average. Again,
out of this 70 per cent. Of precipitation
which reaches the ground in wooded
reas must be deducted the loss by
transportation, 'the process by which
1.-The plant gets rid of the surplus water
a ter having drawn it from the soil in
order to extract from it nutrimenl
which is present in only v,ry highly
attenuated solution. Various in
genious methods have been resortec
to for determining the amount O
moisture used in this way; but, because
# the many factors having to do with
t, the amount for the various kinds o.
vegetation can be indicated only with &
vide margin for variations. Here i,
one of the methods:
"The water transpired comes mostly if mo-
entirely, from the soil. On evaporating i
caves behind it the matters held in solution
la portion of which is inorganic and ii is tina
which constitutes the ash OF the plant Assam
ing that the absorption by the plant is no
sensibly selectiye in the average from larg,
number Of individuals, then a knowledge o
The annual addition Of inorganic material, l. e..
ash, to the forest, and the amount of mnera
matter held in solution by the ground water
will enable us to compute the amount of watel
which has been evaporated."
1t has been estimated that coniferou>
rees transpire only about one tenth as
much, on the average, as deciduou,
ltrees. Thus, in one estimate the
Transportation of the ash Tree during the
period Of vegetation, is put at from soc
TO 600 pounds Of water per pound G.
dry weight of leaves, and OF the spruce
from so to 10 pounds. But, sine,
Transportation is part of the process 0
building up the forest, the water 60
nd of in that way cannot be considered
IS lost for beneficial uses.
While, as it stands now, nobody Cal
say, as result of scientific investiga
ton, whether forests increase the fall 0
rain, snow or dew to an appre ciabl,
extent, there is no room for doubt tina
wooded areas are valuable conservatur
of moisture. In this way they max
the flow Of streams more even
/ and they preserve the conStancy o
. springs. In wooded areas there is ;
! loss by interception and evaporation ii
the foliage and by Transportation ; anc
there is a considerable gain in tn,
protection from evaporation from the
S surface of the ground. 1t is not prob
able that this conservation Of the watel
supply comes anywhere near the mark
drawn by those who hold that the
preservatlJ Of woodland insures al
a1und nee of water supply; but the
, benefits resulting from it are sutfcien
10 be considered among the other eX
cellent reasons for looking well to the
preservation of forests. The effort,
toward arriving at scientific deter
mlnation OF this question are int, rest
my because of the many and various
factors that have to be dealt with al
almost every stage Of the investigation