The sun., 1893-08-05


presence offorests In fiuence this circulation
1t would bo 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
mubt be considered In determining how and
to what extent the rainfall ana 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 earths
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
ma more than the minima, and that
consequently their effect is to make the
average temperature for the year cooler.
Also. their moderating influence Is greater
than their cooling effect. Because the air
above forest regions is slightly cooler than
the strata over treeless tracts. condensa-
tion should be more rapid there 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.
ported by the measurements that have
been made.
Accepting the conclusion that. In general.
forests increase slightly the fall OF rain.
snow, and dew, 1t 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 30 re-
tained 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 thirty per cent. OF the precipi-
tation is thus intercepted and returned to
the atmosphere. or course this intercept
tion and evaporation go on where the sur
face OF the earth is covered by grass and
other growing crops. Whether it Is sufii-
ciently greater In the forest than In the
fields to do away with the excess OF pre-
cipitation 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.
or the 70 per cent. OF rainfall which. 1t
is estimated. reaches the ground In forests.
parti very quickly returned to the atmos-
phere by evaporation. but here the loss is
considerably less than In the open field.
Under certain conditions 1t Is not more
than IS per cent. OF what 1t would be on bare
soil but the conditions are 30 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 areas.
must be deducted the loss by Transportation.
1.-THE process by which the plant gets rid Of
from the soil in order to extract from it the
nutriment which is present in only very
highly attenuated solution" Various in
genious methods have been resorted to for
determining the amount OF moisture used
In this way; but. because OF the many tac-
tors having to do with 1t. the amount for
the various kinds OF vegetation can be In
dicated only with wide margin for varia-
tions. Here is one Of the methods:
"The water transpred mostly II not entirely.
from the soil On evaporatns leaves behind IL the
matters held in solution portion OF which is inorganic
and is that which constitutes the ash Of the plant
Assuming that the absorption BY the plant is not
ssnsibiy ssective in tho from large number
indivduai shea akuowiedge Of annual addition
of inorganic material ash. to tho Forest and the
amount of mineral matter held In solution BY tho
ground water will enable to compute the amount Of
water which has been svaporated"
It las been estimated that coniferous
trees transpire only about one-tenth as
much. on the average. as deciduous trees.
Thus. In one estimate the Transportation Of
the ash tree during the period OF vegeta-
ton, is put at from 500 to 600 pounds of
water per pound Of dry weight Of leaves.
and Of the spruce from so to 10 pounds. But.
since Transportation Is part Of the process Of
building up the forest. the water got rid
Of In that way cannot be considered as lost
for beneficial uses.
While. as 1t stands now. nobody can say,
as result OF scientific investigation. wheth-
er forests increase the fall Of rain. snow, or
dew to an appreciable extent. there Is no
room for doubt that wooded areas are valu-
able conservators Of moisture. In this way
they make the flow Of streams more even.
and they preserve the constancy of springs
In wooded areas there Is loss by intercept
tion and evaporation In the foliage, and by
transpiration; and there Is a considerable
gain In the protection from evaporation
from the surface OF the ground. It
is not probable that this conserve
tion Of the water supply comes any
where near the mark drawn by those
who hold that the preservation Of wood
land insures an abundance OF water supply:
but the benefits resulting from 1t are suffl-
Client to be considered among the other ex-
cellent reasons for looking well to the pres
ervatlon Of forests. The efforts toward ar
irving at a scientific determination Of this
question are reinteresting because of the many
and various factors that have had to be dealt
with at almost every stage OF the investi-
cation. The extreme difficulty of reducing
these factors to known quantities. or even
to rough estimates. has made 1t impossible
to present any array Of figures as result
OF the costly and painstaking work: but
wider knowledge of what has been done
would lead to a greater general interest In
the fascinating subject Of forestry.
If the results Of the scientific investiga-
tions are unsatisfactory vague. there is
no uncertainty In the observations as to