The Hawaiian star. [volume] (Honolulu [Oahu]) 1893-1912, 1893-10-09
NATURAL RAINFALL.
DOES NATURE SLIGHT LAND IF TREES
HAVE BEEN REMOVED?


Started out to soIve--Nrany Scientists OF
Various Countries Have Given the Sub
Ject Much study.
A son of Christopher Columbus once I'M
dertook a task of discovery that proved
much more difficult than that which his
father had tackled so successfully. In a
comparatively short time Christopher had
the solution of his problem. The answer
which his son, Fernando, set out to find is
still missing. But the younger Columbus
thought he had discovered the true rela-
tions of forests to water supplies, and he
announced that the copious rainfall of ia
maica was produced by the islands wealth
of forests and that the decrease of rain in
the Azores and Canaries was because of the
removal of the wooded areas.
For as long perhaps as men have given
any thought to this matter it has been the
common supposition that forests increase
the rainfall within the area of their sup
posed influence, and in that way and other
ways augment I'll flow of brooks and riv.
ers. The earlier efforts to determine through
scientific methods whether there Is any
good ground for the suppostion were made
with appliances so crude that the margin
for error must have been considerably in
excess of the influence, if any, which the in
vestigators hoped to measure. In later
years efforts in the same direction have
been made with great palms, mostly in Eu-
ropean countries, but the problem has been
found to have SO many factors that, al
though the mass of information collected
is extremely interesting, the main question
remains practically unanswered The re.
suits of these efforts, together with some
interesting observations thereon, are set
forth in a bulletin of the forestry division
of the department of agriculture.
Water comes as near being indestructible
as any substance of which we know. Con-
sequently the total quantity of it in the
earth and in the earth's atmosphere is al
ways the same. Only very small percent
age of it is what one of the writers in this
bulletin terms the circulating part of the
earth's water capital. The sun makes vapor
of water that is lying at its level or is on
the way to find its level. This vapor is con-
densed until it is heavier than the air and
starts again toward it's level, and that is
how the circulation goes on. In-what way
does the presence of forests influence this
circulation?
1t would be a long story to tell of the
methods employed in France, Germany
Sweden, Austria and other countries of Eu-
rope to measure the various influences that
must be considered in determining how and
to what extent the rainfall and the flow of
streams are affected by the presence of for
ests. A very important factor, since heat
is what starts the movement of the earth's
circulating water capital is the matter of
temperature, and the results of the iuvesti-
cations seem to show beyond dispute that
forests reduce the maxima and the minima
of temperature, that they reduce the maxi
ma more than the minima, and that conse-
quently their effect is to make the average
temperature for the year cooler.
Also, their moderating influence in great
er than their cooling effect. Because the
air above forest regions is slightly cooler
than the strata over treeless tracts, con
densation should be more rapid than over
open fields, and the rainfall should be
greater These cooler bodies of air, being
blown over adjacent regions that are not
wooded, should also increase somewhat the
precipitation there. That is the theory,
and it seems to be in some degree support
ed by the measurements that have been
made.
Accepting the conclusion that, in general,
forests increase slightly the fall of rain,
snow and dew, it remains to be determined
bow much of this increase is available for
beneficial purposes Part of it is inter
cepted by foliage, and is returned to the
atmosphere by evaporation without having
reached the ground. The proportion SO re-
tanned varies with the nature of the foliase,
the density of the forest and the season of
the year. The retention by evergreen trees
Is less than by deciduous. 1t is estimated
that perhaps 80 per cent of the precipitation
is thus intercepted and returned to the at
mosphere. OF course this interception and
evaporation go ON where the surface of
the earth is covered by grass and other
growing crops. Whether it is sufficiently
greater in the forest than in the field to do
away with the excess of precipitation on
wooded tracts over that on cleared areas is
an unsettled question.
OF the 30 per cent of rainfall which, it is
estimated, reaches the ground in forests, q
part is very quickly returned to the atmos
phere by evaporation, but here the loss il
considerably less than in the open field
Under certain conditions it is not more thar
13 per cent of what it would be on bare soil
but the conditions are so various that it Ii
difficult to arrive at an average. Again, ou
of this 20 per cent of precipitation which
reaches the ground in wooded areas mus
be deducted the loss by Transportation, 'th
process by which the plant gets rid of thu
surplus water after having drawn it from
the soil in order to extract from it tn
nutriment which is present in only yer.
highly attenuated solution" Various in
genious methods have been resorted to TO
determining the amount of moisture use'
In this way, but because of the many fac
tors having to do with it, the amount TO
the various kinds of vegetation can be in
dictated only with wide margin for varia
lions.
While as it stands now nobody can say
as result of scientific investigation
whether forests increase the fall of rain
snow or dew to an appreciable extent, ther
is no room for doubt that wooded areas ar
valuable conservators of moisture In thi
way they make the flow of streams NOR
even, and they preserve the constancy c
springs In wooded areas there is a loss b.
interrogation and evaporation in the foliag
and by Transportation, and there is u consd
cradle gain in the protection from eyapors
ton from the surface of the ground 1t
not probable that this conservation of til
water supply comes anywhere near til
mark drawn by those who hold that tn
preservation of woodland insures an abuI
dance of water supply, but the benefits n
sulting from it are sufficient to be consit
cred among the other excellent reasons fc
looking well to the preservation of forests
New York Sun.
Years Railroad Losses.
Colonel II G. prOut editor of The Raj