The Helena independent. [volume] (Helena, Mont.) 1875-1943, 1893-08-29
WHAT CAUSES RAINFALL?
Is II True That Nature Sights
Lands When the Trees
Are Removed2
A Problem That the Son OF
Columbus Started Out
to Solve.
Many Scientists in Various Countries Have
Given tho Subject n Great Deal
of study,

A son of Christopher Colnnib bus once I'M
lertook 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 md Canaries was because of the
removal of the wooded areas.
For ms long perhaps rs men have given
any thought to this matter it has been the
common superstition that forests increase
the rainfall within the area of their sup
posed influence, and in that way and other
ways augment tie flow of brooks and riv-
ers. The earlier efforts to determine through
scientific methods whether there is any
good ground for the supposition were made
with appliances so crude that the margin
for error must nave keen 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 pains, 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. on
sequently the total quantity of it in the
earth and in the earth's atmosphere is al
ways the same. Only a very small percent
age of it is what one of the writer's 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-
denssd until it is heavier than the air and
starts again toward its 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 undermining 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 ~investi-
cations seem to show beyond dispute that
forests reduce the maNima and the minima
of temperature, that they reduce the maxi
ina more than the minina, and that conse-
quently their effect is to make the average
temperature for the year cooler.
Also, their moderating influence in great
n fhpy, thnir onn1i,n~ afant p,1o,,,, H.,
air above forest regions is slightly cooler
than the strata over ~treeless tracts, CON
densation should be moro 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,
n it seems to be in some degree support
ed by the measurement 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
how 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 foliage,
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 in~tercepJion and
evaporation go OF 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 70 per cent Of rainfall which, it is
estimated, reaches the ground in forests, a
part is very quickly returned to the atmos-
phere by evaporation, but here the loss is
considerably less than in the open field.
Under certain conditions it is not more than
ID 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 20 per cent of precipitation which
reaches the ground in wooded areas must
be deductSd the loss by Transportation, the
process by which the plant gets rid of the
surplus water after having drawn it from
the soil in order to extract from it the
nutrimcnt which is present in only a very
highly attcnuated solution" Various III
genious methods have been rcsorted to for
determining the amount of moisture used
in this way, but because Of the many fac
tors having to do with it, the amount for
the various kinds of vegetation can be in
dictated only with a wide margin for yaria-
lions.
While as it stands now nobody can say,
as u result Of scientific investigation,
whether forests increase the fall Of rain,
snow or dew TO auappreciable extent, there
Is no room for doubt that wooded areas are
VALUABLE conserVators of moisture. In this
way they make the flow of streams more
even, and they preserve the consistency of
springs. In wooded areas there is q loss by
lnterccptlon and evaporation in the fOliugu
and by Transportation, and there is a consid-
cradle gain in the protection from evapora-
ton from the surface of the ground. 1t is
not probable that this conservation of the
water supply comes anywhere hear the
mark drawn by those who hold that the
preservation of woodland iusures an album
dance of water supply, but the benefits re-
sultlIg from it are sufficient to be consid-
cred among the other excellent reasons for
looking well to the preservation of forests.
New York Sun.