^18 
Supplement to the " Tropical Agriculturist'^ [Sspt. 2, 1901. 
regions behind these forests drier and unable 
to yiel d a further supply of water." 
It is thus Oskar Peschel teaches in his well- 
known work " Neue Probleme der Tergleichea 
den Erdkunde," but he entii'ely omits from his 
calculation re-evni)oration of moisture precipi- 
tated on the land, and his conclusions cannot 
consequently be accepted. A well-wooded forest 
area may best be compared to a landlord who 
spends bis income derived from the country within 
it and for the benefit of his neighbours where 
as cleared areas resemble absentee proprietors 
who scatter tl'eir revenues in foreign parts. 
It rains ; the drops are scattered on the leaves 
and fall in a soft gentle spray or in slow falling 
big drops, which have collected on the foliage 
on to the spongy forest ground. The water 
has thus time to percolate slowly into the soil 
below, whence a large quantity is gradually 
pumped up again through the roots of the forest 
trees exhaled by their leaves and again assists 
in forming rain clouds. Wooded areas, no doubt, 
extract under the same circumstances more mois- 
ture out of the air than for disforested regions, 
but they serve as a store-house and yield again 
what they take, "whereas a great portion of 
the water precipitated on barren soil is only 
recovered by evaporation from rivers, lakes, and 
oceans. Forests use, therefore, much less naoisture 
than barren areas in the same position and under 
similar conditions and augment the atmospheric 
moisture in regard to regions vhich are separated 
by such forests from the sea instead of diminish- 
ing it. Their action in this respect is not the 
same time as that of an intervening mountain 
range. 
In Assam, which is a-broad, isolated, well-wooded 
valley, rain clouds form in the winter and it 
rains when no air currents reach it from the 
sea. The clouds are home-born and are to some 
extent, at least, due to re-evaporation from the 
•vast forest areas still in existence. The same 
laws naturally apply to any locality, though they 
may not be so strikingly exemplified. It may 
be argued that evaporation from open ground 
is much more intense than from soil covered by 
forests. No doubt this is the case, and Eber- 
mayer in his "die Physikalishen E'nwirkungen 
des Waldes auf Luft und Boden" gives the 
following data : -"The forest alone, without the 
cover or dead leaves diminishes the evaporations 
by 62 per cent, as compared with that in the 
open. Evaporation is consequently 2*6 times less 
in the forests, A covering of dead leaves and 
vegetable mould diminishes evaporation by a 
further 22 per cent. Forests with an undis- 
turbed covering of dead leaves and vegetable 
mould lessen the -evaporation as compared with 
that in the open by 84 per cent. 
These data are based on observations made in 
Bavaria during the summer months. In the 
Indian climate the difference, which iucreases 
in proportion to the heat and dryness of the 
atmosphere would be even more considerable. 
The above data refer to the evaporation from 
the soil, which, of course, can only take place 
as long as there is water on the surface which 
in the open is not the case for long, as it either 
jlows ofi.' or gra'vittttea out of reagb. of the iuflueuqe 
of evaporation. In a forest the water does not 
flow off with the same rapidity, and much of 
that which gravitates into the soil is pumped 
back by the long roots of the forest trees, and 
especially during the period of vegetation is 
exhaled by the leave? in quantities which repre- 
Fent far more than the moisture evaporated from 
the open ground. There can be no doubt, what- 
ever may be said to the contrary, that the widely- 
spread notion that forests tend to increase the 
rainfall, and that in a warm country, diminishes 
its moisture, and consequently its fertility is 
correct. As already pointed out the theory is 
proved by history and ruins, and the rapidity 
with which changes in the climate of different 
countries have taken place entirely forbids 
that such sudden modifications should be ascribed 
to cosmic causes. We accept other scientific 
problems on such more flimsy evidence, but in 
tliis instance a large number of us suddenlj' swerve 
aside and follow a school which starts new theories 
on partial observations and leaves re-evapora- 
tion out of consideration. Ebermayer fonnd from 
experiments made that during July, the hottest 
month in Bavaria, only 6 per cent which filtered 
down to the depth in a forest, the ground of 
which was covered with complete and undisturbed 
vegetable mould. 
In the one case the water rapidly runs off 
into streams and seas by sudden floods and 
freshets, and this too when the whole atmosphere 
is surcharged with moisture. In the other 
instance the water is stored for re-evaporation 
through the foliage of the forests, and is given 
forth at the time when the air is drier and the 
winds do not blow from the sea. It may be 
safely stated that more than the rain which is thug 
stored in the ground is re-evaporated by the trees 
in time of need, and even at this low computation 
a well-stocked, a well-protected forest area, the 
vegetable mould of which is undisturbed by 
either fire or the axe or rake of the " rab " or 
"sir"' collector would re-supply to the atmosphere 
at least one-third of the moisture which ia 
precipitated on it. This would be available for 
the open country. If therefore 30 per cent of the 
country was under complete forest, the rainfall 
should increase by 10 per cent under conditions 
similar to those which exist in Bavaria in July. 
In India, or any other country with such a fierce 
climate as ours, the influence should be more markd. 
The monsoons in India, it is argued, must be 
quite independent of forest growth. Quite so. 
Forests can have no influence whatever on the 
amount of moisture drawn from the ocean, and 
the general direction of the winds is unques- 
tionably governed by greater causes, but, apart 
from this, periodical rains are subject to the same 
general laws as all other rains, and must, therefore, 
be afl'ected by the same causes, and amongst thorn 
by extensive forest growth, in exactly the same 
way and degree. The air may be charged with 
moisture which need not, however, be precipitated. 
If an extensive snowfall in the outer Himalayas 
can affect the monsoon rainfall, it seems certain 
that forests can do the same, though probably not 
to the same degree. 
[Forestry in British India by B. ElBBBNXftgp,] 
{T<i JiQ cortcfttc?e(?.]| 
