There is a spot which I used to visit some years ago, that seemed to me
one of the most enchanting of natural scenes. It was a level plain of
about ten acres, surrounded by a narrow stream that was fed by a steep
ridge forming a sort of amphitheatre round more than half its
circumference. The ridge was a declivity of near a hundred feet in
height, and so steep that you could climb it only by taking hold of the
trees and bushes that covered it. The whole surface consisted of a thin
stratum of soil deposited upon a slaty rock; but the growth of trees
upon this slope was beautiful and immense, and the water that was
constantly trickling from a thousand fountains kept the ground all the
year green with mosses and ferns, and gay with many varieties of
flowers. The soil was so rich in the meadow enclosed by this ridge, and
annually fertilized by the _débris_ washed from the hills, that the
proprietor every summer filled his barns with hay, which was obtained
from it without any cultivation.
I revisited this spot a few years since, after a long period of absence.
A new owner, “a man of progress and enterprise,” had felled the trees
that grew so beautifully on the steep sides of this elevation, and
valley and hill have become a dreary and unprofitable waste. The thin
soil that sustained the forest, no longer protected by the trees and
their undergrowth, has been washed down into the valley, leaving nothing
but a bald, rocky surface, whose hideousness is scarcely relieved by a
few straggling vines. The valley is also ruined; for the inundations to
which it is subject after any copious rain destroy every crop that is
planted upon it, and render it impracticable for tillage. It is covered
with sand heaps; the little stream that glided round it, fringed with
azaleas and wild roses, has disappeared, and the land is reduced to a
barren pasture.
The general practice of the pioneers of civilization on this continent
was to cut down the wood chiefly from the uplands and the lower slopes
of the hills and mountains. They cleared those tracts which were most
valuable for immediate use and cultivation. Necessity led them to pursue
the very course required by the laws of nature for improving the soil
and climate. The first clearings were made chiefly for purposes of
agriculture; and as every farm was surrounded by a rampart of woods, it
was sheltered from the force of the winds and pleasantly open to the
sun. But when men began to fell the woods to supply the demands of towns
and cities for fuel and lumber, these clearings were gradually deprived
of their shelter, by levelling the surrounding forest and opening the
country to the winds from every quarter. But the clearing of the wood
from the plains, while it has rendered the climate more unstable, has
not been the cause of inundations or the diminution of streams. This
evil has been produced by clearing the mountains and lesser elevations
having steep or rocky sides; and if this destructive work is not checked
by legislation or by the wisdom of the people, plains and valleys now
green and fertile will become profitless for tillage or pasture, and the
advantages we shall have sacrificed will be irretrievable in the
lifetime of a single generation. The same indiscriminate felling of
woods has rendered many a once fertile region in Europe barren and
uninhabitable, equally among the cold mountains of Norway and the sunny
plains of Brittany.
Our climate suffers more than formerly from summer droughts. Many
ancient streams have entirely disappeared, and a still greater number
are dry in summer. Boussingault mentions a fact that clearly illustrates
the condition to which we may be exposed in thousands of locations on
this continent. In the island of Ascension there was a beautiful spring,
situated at the foot of a mountain which was covered with wood. By
degrees the spring became less copious, and at length failed. While its
waters were annually diminishing in bulk, the mountain had been
gradually cleared of its forest. The disappearance of the spring was
attributed to the clearing. The mountain was again planted, and as the
new growth of wood increased, the spring reappeared, and finally
attained its original fulness. More to be dreaded than drought, and
produced by the same cause,—the clearing of steep declivities of their
wood,—are the excessive inundations to which all parts of the country
are subject.
If it were in the power of man to dispose his woods and tillage in the
most advantageous manner, he might not only produce an important
amelioration of the general climate, but he might diminish the frequency
and severity both of droughts and inundations, and preserve the general
fulness of streams. If every man were to pursue that course which would
protect his own grounds from these evils, it would be sufficient to
bring about this beneficent result. If each owner of land would keep all
his hills and declivities, and all slopes that contain only a thin
deposit of soil or a quarry, covered with forest, he would lessen his
local inundations from vernal thaws and summer rains. Such a covering of
wood tends to equalize the moisture that is distributed over the land,
causing it, when showered upon the hills, to be retained by the
mechanical action of the trees and their undergrowth of shrubs and
herbaceous plants, and by the spongy surface of the soil underneath
them, made porous by mosses, decayed leaves, and other _débris_, so that
the plains and valleys have a moderate oozing supply of moisture for a
long time after every shower. Without this covering, the water when
precipitated upon the slopes, would immediately rush down over an
unprotected surface in torrents upon the space below.
Every one has witnessed the effects of clearing the woods and other
vegetation from moderate declivities in his own neighborhood. He has
observed how rapidly a valley is inundated by heavy showers, if the
rising grounds that form its basin are bare of trees and planted with
the farmer’s crops. Even grass alone serves to check the rapidity with
which the water finds its way to the bottom of the slope. Let it be
covered with bushes and vines, and the water flows with a speed still
more diminished. Let this shrubbery grow into a forest, and the valley
would never be inundated except by a long-continued and flooding rain.
Woods and their undergrowth are indeed the only barriers against
frequent and sudden inundations, and the only means in the economy of
nature for preserving an equal fulness of streams during all seasons of
the year.
At first thought, it may seem strange that the clearing of forests
should be equally the cause both of drought and inundations; but these
apparently incompatible facts are easily explained by considering the
different effects produced by woods standing in different situations. An
excess of moisture in the valleys comes from the drainage of the hills,
and the same conditions that will cause them to be dried up at certain
times will cause them to be flooded at others. Nature’s design seems to
be to preserve a constant moderate fulness of streams and standing
water. This purpose she accomplishes by clothing the general surface of
the country with wood. When man disturbs this arrangement, he may
produce evil consequences which he had never anticipated. We are not,
however, to conclude that we may not improve the soil and climate by
changing the original condition of this wooded surface. The clearing of
the forest may be reduced to a science whose laws are as sure and
unexceptionable as those of mechanics and hydraulics. Though it has not
gained much attention from the public mind, it is well understood by the
learned who have made this branch of vegetable meteorology their special
study. Our danger lies in neglecting to apply these laws to operations
in the forest, and in preferring to obtain certain immediate commercial
advantages, at the risk of inflicting evils of incalculable extent upon
a coming generation.