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7

tion of forests in these respects exer-
cises a terribly baneful influence upon
the country that has once, prodigal-like,
sold its birthright of trees without mak-
ing any provision to repair their loss in
the future. To put it briefly, the worst
effect of deforestation is

EROSION.

To estimate the full significance of this
term, we must consider briefly the
part played by trees in all natural sys-
tems of drainage and water supply. Here
I may quote Professor Schwappach again:
"The water from heavy rains, checked
in its descent by meeting first with the
foliage of trees, is better retained on
forest soil than on bare land. Under a
close cover of trees, there collects a
'humus' soil formed from the decay of
fallen leaves. Through this sponge-like
soil-covering the rain water slowly filters,
and its passage is further retarded by
the stems and roots of the trees. In
this way the erosive effects of violent
rains upon bare hillsides is obviated.
This is often a very serious danger, not
only because the good soil is washed
away, but also on account of lower-
lying fertile lands being covered by
boulders, gravel, and sand brought down
in the flooded waters." With this state-
ment of the case, we may compare the
following extract from Captain Campbell

Walker's paper, which, as mentioned
above, bears more especially upon the
effects of deforestation in this country.
"The forests by their presence act as
storehouses of moisture, both from their
leafy canopy which covers the earth,
and the bed of dead leaves on its sur-
face, the loss of moisture by evaporation
being by these means reduced to one-
fifth; and, further, the bed of dead leaves
acts as a sponge soaking up and retain-
ing the rain and regulating its distribu-
tion, while the roots not only act as
vertical drains promoting the descent of
the water into the lower strata of the
earth, there to nourish the springs, but
bind the soil on the mountain sides
together, and prevent its being carried
away into the valley below." It should
now be clear what difference forests
make to a country's river system and
its soil. They store up water for
gradual distribution; and they prevent
the vegetable mould they form from
being washed away. Consequently, it
follows that when the bush is cut down,
not only do streams tend to disappear
with it, but the rain, when it comes,
carries the fertile soil from the hillsides
down into the valleys, and at the same
time, rushing unimpeded along the
channels and courses that the storm-
water has already excavated in the earth,
causes sudden and disastrous floods.