Soil erosion

“ Whenever the force with which the water moves along is stronger than the cohesion of the soil, erosion occurs. This erosion will continue, the channel of the stream becoming ever deeper, until a soil is encountered whose resistance is equal to the erosive action of the water. As the alluvion is carried on, the slope of the stream will become steeper and steeper the higher one goes. ”

“ When vegetation is completely removed by excessive erosion, it is an open question whether the resulting habitat is to be regarded as new or denuded. Erosion is rarely so extreme and so rapid, however, as to produce such a condition, even when it results from cultivation or deforestation. It is, moreover, especially characteristic of newly formed soils, and in studying succession in eroded habitats, it is fundamentally important to determine whether erosion has produced denudation, or has operated upon a new soil. ”

“ Uncontrolled logging and fire can strip the land of its porous cover, leaving it unable to absorb water. The disastrous consequences are soil erosion, flash floods, and muddy streams. Thus, as soil conditions require, the forester may plan light to moderate selection cuttings. ”

“ The process may be observed in miniature in the wash of the soil in Tennessee fields. The weathering of rock in to soil, erosion with its transportation of the products of weathering, deposition of the material in the oceans or in large bodies of fresh water, uplift of the ocean's floors and its hardening into rock may all be seen in slow but certain progress in various parts of the world at the present day, and their occurrence in the past is recorded in the rocks. ”

“ It is often assumed that there is no soil erosion beneath tropical rainforest. However, under certain conditions where there is very little plant ground cover, soil protection is dependant on leaf litter and other fallen vegetation. ”

“ Soil erosion does not result from forest cutting in itself, but in cultivation, using that term in its broadest sense. The question of preventing such erosion of soil-wash is alto- gether one of dispensing with cultivation or properly con- trolling. The natural growth which always follows the de- struction of a forest is fully as effective in preventing erosion, and even retaining run-off, as the natural forest. ”

“ At an early stage in its erosion history, before an upland has been dissected by valleys, nearly all of it may be arable. Later, when drainage is at its maturity, and when hillsides and ridge slopes constitute a large part of the area, there is probably the least acreage of arable land. This is especially true if the slopes are so steep as to allow the soil to be readily washed away. At a still later stage, when the valley bottoms have become wide and the slopes of the ridges and hills so reduced as to be available, the area of cultivable land is again increased. ”

“ After the trees have been cut away, very often, especially upon hillsides, the most productive soil is washed away, usually clear off of the original owner's farm, and deposited in the flood-plains or bottoms of creeks and rivers or in river deltas—in places where it cannot be utilized to any great extent. Thus erosion causes a tremendous loss to farmers, and it is chiefly due to the thoughtlessness of the American people in destroying the forests. ”

“ EROSION It is not always realized how important to our welfare the forests are, especially from the point of view of agricultural production. A very large part of the timbered area of the United States is in small woodlands on privately owned farms. Not only are the timber resources themselves of great value, but the relation of woodland to agriculture is very close, especially in its effect upon soil erosion. ”

“ The same forces have meant that traditional shifting cultivators, who once cut forests, grew crops, and then gave the forest time to recover, now have neither land enough nor time to let forests re-establish. So forests are being destroyed, often only to create poor farmland that cannot support those who till it. Extending cultivation onto steep slopes is increasing soil erosion in many hilly sections of both developing and developed nations. ”

“ In many places after the timber has been cut off gullies and washes start in the old wheel ruts, log slides, etc., and these and other forms of erosion can best be prevented by leaving the brush on the ground, either laid in the incipient washes or scattered over the soil that is likely to wash. Brush burning destroys the valuable soil cover, and on the spots where the piles are burned the soil is loosened, which renders it even more liable to erosion. ”

“ Surface-erosion cuts through the finer superficial layer, into the pebble-layer beneath, leaving, however, portions of the superficial layer as mounds. The size of the mounds depends on the thickness of the superficial layer; their shape depends much on the slope of the surface. The process once started, small shrubs and weeds take possession of the mounds, as the better soil, and hold them by their roots, and thus increase their size, by preventing or retarding erosion. ”

“ The soil was washed away by every rain and carried by thousands of cataracts into the river. Only when the country reaches the "base level of erosion," as the Major called it, would vegetation succeed in holding its place; that is when the declivity of the surrounding region became reduced till the rain torrents should lack the velocity necessary to transport any great load of detritus, and the disintegrated material would accumulate, give a footing to plants, and thus further protect itself and the rocks. ”

“ Once the hilly terrain south of Dayton was covered with bunchgrass, but with the discovery that heavy yields of wheat and barley could be grown on these benchlands, all but the steepest hillsides were put under cultivation. Soon both wind and water erosion began to take their toll. Deep gullies began to appear, and during the spring freshets every little rivulet carried away part of the fine top soil. Today most farmers, aided by the various State and Federal conservation agencies, have adopted farming techniques that are reducing the amount of soil loss due to erosion. ”

“ This soil resource destruction from erosion leads to the destruction of other valuable resources. We appear to be upon the eve of an epoch of waterway construction and experiment. The greatest injury to waterways is channel filling by down-washed mud. ”

“ The tea orchards as we saw them on the steeper slopes, not level-terraced, are often heavily mulched with straw which makes erosion, even by heavy rains, impossible, while the treatment retains the rain where it falls, giving the soil opportunity to receive it under the impulse of both capillarity and gravity, and with it the soluble ash ingredients leached from the straw. ”

“ Under the mild, humid climate that prevails, more especially from the vicinity of the Susquehanna River southward, the rocks are deeply disintegrated and decayed, and even steep mountainsides are mantled with soil and rock débris. It is the excess of disintegration and decay over erosion which gives to the mountains their usually flowing outlines and pleasingly picturesque rather than rugged scenery. The valleys still retain much of the material washed from the uplands, and are deeply floored with rich soil. ”

“ Man's "improvement" of the soil increased the erosion from its surface; his arrangements for confining the lateral spread of the water in floods compel the rivers to transport to their mouths the earth derived from that erosion even in their upper course; and, consequently, the sediment they deposit at their outlets is not only much larger in quantity, but composed of heavier materials, which sink more readily to the bottom of the sea and are less easily removed by marine currents. ”

“ In some localities the soil may accumulate to a considerable depth, allowing the processes of weathering to go to an extreme; in others the processes may be interrupted by erosion, which sweeps off the weathered products at intermediate stages of decomposition and may leave a very thin and little decomposed soil. ”

“ In compact soils, the plants of the initial formations not merely break the impact of the raindrops, but, what is much more important, they delay the downward movement of the water, and produce numberless tiny streams. The delayed water is largely absorbed by the soil, and the reduction of the run-off prevents the formation of rills of sufficient size to cause erosion. As in dunes, such plants are usually perennial grasses, though composites are frequent ”

“ The result of this erosion and transportation has been to change the conditions of the surface both as regards soil and drainage. As the reader has doubtless perceived, ordinary soil is, outside of the river valleys, derived from the rock beneath where it lies. In glaciated districts the material is commonly brought from a considerable distance, often from miles away. These ice-made soils are rarely very fertile, but they commonly have a great endurance for tillage, and this for the reason that the earth is refreshed by the decay of the pebbles which they contain. ”

“ The forest burned to destruction can rise again if the soil remains. Some examination will show that the most vital part of the whole conservation matter is the preservation of the soil, [Pg 31] and that soil conservation is 99 per cent the prevention of erosion. Soil robbery by unscientific agriculture can go to its most extreme lengths and reduce the soil to the depths of non-productivity; but scientific agriculture can, by the addition of humus and some fertilizer, soon restore such soil to high fertility. ”

“ But once the gully removes this soil, it is the end so far as our civilization is concerned—forest, field and food are impossible and even water power is greatly impaired. Our present system of agriculture, depending upon the grains, demands the plowing of hillsides and the hillsides wash away. This present dependence upon the plow means that one-third of our soil resources is used only for forest, one-third is being injured by hillside erosion, and only one-third, the levelest, is being properly used for plow crops. ”

“ Others are convinced they are formed by the piling up of earth around a bush, clump of grass, stone, or other object acting as a nucleus about which wind-borne material may accumulate—overlooking the fact that clay, gravel, or gumbo soil can not be carried by wind, and that lighter soil or sand will form elongated instead of circular masses. Another supposition is that they are due to stream erosion; flood waters washing away the soil between them and thus leaving the earth composing the mound in its original position. ”

“ In other words, the waste mantle also is now graded, and as waterfalls have been effaced in the river beds, so now any ledges in the wide streams of waste are worn away and covered beneath smooth slopes of fine soil. Ground water stands high and may exude in areas of swamp. In youth the land mass was roughhewn and cut deep by stream erosion. In old age the faint reliefs of the land dissolve away, chiefly under the action of the weather, beneath their cloak of waste. ”

“ The work itself will cover a wide field including clearance of slums, which for adequate reasons cannot be undertaken by private capital; in rural housing of several kinds, where, again, private capital is unable to function; in rural electrification; in the reforestation of the great watersheds of the Nation; in an intensified program to prevent soil erosion and to reclaim blighted areas; in improving existing road systems and in constructing national highways designed to handle modern traffic; in the elimination of grade crossings; ”

“ Where waste sources are too diffuse to be channeled into collection systems—as along many agricultural streams heavily polluted through land runoff and drainage, and also in some urban situation—present tools are extremely limited. Soil conservation practices aimed at cutting down erosion—to be discussed within a few pages—tend to keep not only silt but nutrients and other substances on the land to some extent. ”

“ The site of this orchard seems nearly level to the casual eye; yet slope, with its accompanying erosion, together with differences in depth of soil, have created nearly as large differences in growth and yield as any treatment. Good treatments have nearly offset the initial disadvantage of poor soil; but it is more economical to plant the orchard on good soil than to attempt the improvement of a poor soil. ”

“ Buried valleys may be observed in a number of places on the canyon walls, where subsequently lava flows displaced the streams and initiated new drainage systems. In these quiet intervals the weathering agents attacked the rock surfaces and formed soil. There were at least three or four such prolonged periods of weathering and erosion wherein a land surface was exposed for many thousands of years, stream systems organized, and a cultivable soil formed. No evidence has been found, however, that man was there to cultivate the soil. ”

“ Clearing an area of forest vastly reduces the amount of vegetation protecting the soil from rainfall damage. It also largely removes the 'sponge' that moderates the release of rainwater into river systems. The result is increased erosion and increased sediment loads carried by rivers, and therefore an increase in the amount of sediment available for deposition. ”

“ Discing, which mixes stubble with the soil, is supplementing plowing; strip farming reduces wind erosion; contour cultivation slows up drainage and conserves both soil and water. Gully erosion has been checked by planting grass, alfalfa, and clover on vulnerable slopes; these crops either are used for forage or plowed under
to add humus to the soil. Steep slopes and possible water courses are not cultivated. LEWIS AND CLARK TRAIL STATE PARK (camping facili- ties) , 74.7 m., is a 50-acre, partially improved tract adjacent to the highway and the Touchet River. ”