MOUNTAIN ASH.
RELATIONS OF TREES TO WATER.
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.