Evening journal., 1893-09-05
NATURAL RAINFALL.
DOES NATURE SLIGHT LAND IF TREES
HAVE BEEN REMOVED?

ject Much study.
A son Of Christopher Columbus once un-
iertook task of discovery that proved
much more difficult than chat which his
father had tackled so successfully. In
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 il has been the
common suppostion that forests increase
the rainfall within the area of their sup
posed influence and in that way and other
ways augment the flow of brooks and riv.
ers Theearlier 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 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
NNAii llttNA Mllu NAtAN llallln llN0NiN III l4u-
ropean countries, but the problem has been
found 20 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 q 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 10 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 il 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 in determining how and
TO what extent the rainfall and the flow Of
streams are affected by the presence of for
esis 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 maXima and the minima
of temperature, that they reduce the maxi
ina more than the minima, and that conse-
quenlly their effect is to make the average
| ,r,rtnt m 80 Cor ha trn,. o,alor
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 il 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
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 10 the at
| mosphere. OF course this interception and
evaporation 60 on where the surface of
the earth is covered by grass and other
growing crops Whether IL 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 20 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
l3 per cent OF what IL would be on bare soil,
but the conditions are so various that il is
difficult TO arrive 40 an average. Again. out
of this 20 per cent of precipitation which
reaches the ground In wooded areas must
be deducted the loss by Transportation, "the
process by which the plant gets rid Of the
surplus water after having drawn il from
the soil ia order to extract from il the
nutriment which is present in only a very
highly attenuated solution" Various ia
genious methods have been resorted to for
determining the amount Of moisture used
in this way, but because Of the many fac
tors having to do with IL, the amount for
the various kinds Of vegetation eau be in
dictated only with a wide margin for varia
tions.
While as it stands now nobody can say
RS result of scientific investigation
, whether forests increase the lall of rain
snow or dew to an nappreciable extent. thcr,
is no room for doubt that wooded areas are
, valuable conservators of moisture In thi,
way they make the flow of streams NOR,
even, and they preserve the constancy o
I springs. In wooded areas there is a loss b,
interception and evaporation ia the foliag,
and by Transportation, and there is a consd
erable gain in the protection from evapora
tion from the surface of the ground. Il !,
not probable that this conservation of The
water supply comes anywhere near tn,
mark drawn by those who hold that th,
preservation of woodland insures an album
dance Of water supply, but the benefits re
sulting from IL are sufficient to be consid
cred among the other excellent reasons io
looking well 20 the preservation Of forests
-Natv Xarlt Cun