The Earth as Modified by Human Action

by George P. Marsh

The period of cutting coppices varies in Europe from fifteen to forty years, according to soil, species, and rapidity of growth. In the futaie, or full-growth system, the trees are allowed to stand as long as they continue in healthy and vigorous growth. This is a shorter period than would be at first supposed, when we consider the advanced age and great dimensions to which, under favorable circumstances, many forest-trees attain in temperate climates. But, as every observing person familiar with the forest is aware, these are exceptional cases, just as are instances of great longevity or of gigantic stature among men. Able vegetable physiologists have maintained that the tree, like most fish and reptiles, has no natural limit of life or of growth, and that the only reason why our oaks and our pines do not reach the age of twenty centuries and the height of a hundred fathoms, is, that in the multitude of accidents to which they are exposed, the chances of their attaining to such a length of years and to such dimensions of growth are millions to one against them. But another explanation of this fact is possible. In trees affected by no discoverable external cause of death, decay begins at the topmost branches, which seem to wither and die for want of nutriment. The mysterious force by which the sap is carried from the roots to the utmost twigs, cannot be conceived to be unlimited in power, and it is probable that it differs in different species, so that while it may suffice to raise the fluid to the height of five hundred feet in the eucalyptus, it may not be able to carry it beyond one hundred and fifty in the oak. The limit may be different, too, in different trees of the same species, not from defective organization in those of inferior growth, but from more or less favorable conditions of soil, nourishment, and exposure. Whenever a tree attains to the limit beyond which its circulating fluids cannot rise, we may suppose that decay begins, and death follows from want of nutrition at the extremities, and from the same causes which bring about the same results in animals of limited size—such, for example, as the interruption of functions essential to life, in consequence of the clogging up of ducts by matter assimilable in the stage of growth, but no longer so when increment has ceased. In the natural woods we observe that, though, among the myriads of trees which grow upon a square mile, there are several vegetable giants, yet the great majority of them begin to decay long before they have attained their maximum of stature, and this seems to be still more emphatically true of the artificial forest. In France, according to Clave, "oaks, in a suitable soil, may stand, without exhibiting any sign of decay, for two or three hundred years; the pines hardly exceed one hundred and twenty, and the soft or white woods [bois blancs], in wet soils, languish, and die before reaching the fiftieth year." [Footnote: Etudes Forestieres, p. 80.] These ages are certainly below the average of those of American forest-trees, and are greatly exceeded in very numerous well-attested instances of isolated trees in Europe.

The former mode of treating the futaie, called the garden system, was to cut the trees individually as they arrived at maturity, but, in the best regulated forests, this practice has been abandoned for the German method, which embraces not only the securing of the largest immediate profit, but the replanting of the forest, and the care of the young growth. This is effected in the case of a forest, whether natural or artificial, which is to be subjected to regular management, by three operations. The first of these consists in felling about one-third of the trees, in such way as to leave convenient spaces for the growth of seedlings. The remaining two-thirds are relied upon to replant the vacancies, by natural sowing, which they seldom or never fail to do. The seedlings are watched, are thinned out when too dense, and the ill-formed and sickly, as well as those of species of inferior value, and the shrubs and thorns which might otherwise choke or too closely shade them, are pulled up. When they have attained sufficient strength and development of foliage to require, or at least to bear, more light and air, the second step is taken, by removing a suitable proportion of the old trees which had been spared at the first cutting; and when, finally, the younger trees are hardened enough to bear frost and sun without other protection than that which they mutually give to each other, the remainder of the original forest is felled, and the wood now consists wholly of young and vigorous trees. This result is obtained after about twenty years. At convenient periods, the unhealthy stocks and those injured by wind or other accidents are removed, and in some instances the growth of the remainder is promoted by irrigation or by fertilizing applications. [Footnote: The grounds which it is most important to clothe with wood as a conservative influence, and which, also, can best be spared from agricultural use, are steep hillsides. But the performance of all the offices of the forester to the tree—seeding, planting, thinning, trimming, and finally felling and removing for consumption—is more laborious upon a rapid declivity than on a level soil, and at the same time it is difficult to apply irrigation or manures to trees so situated. Experience has shown that there in great advantage in terracing the face of a hill before planting it, both as preventing the wash of the earth by checking the flow of water down its slope, and as presenting a surface favorable for irrigation, as well as for manuring and cultivating the tree. But even without so expensive a process, very important results have been obtained by simply ditching declivities. "In order to hasten the growth of wood on the flanks of a mountain, Mr. Eugene Chevandier divided the slope into zones forty or fifty feet wide, by horizontal ditches closed at both ends, and thereby obtained, from firs of different ages, shoots double the dimensions of those which grew on a dry soil of the same character, where the water was allowed to run off without obstruction."—Dumont, Des Travaux Publics, etc., pp. 94-96. The ditches were about two feet and a half deep, and three feet and a half wide, and they cost about forty francs the hectare, or three dollars the acre. This extraordinary growth was produced wholly by the retention of the rain-water in the ditches, whence it filtered through the whole soil and supplied moisture to the roots of the trees. It may be doubted whether in a climate cold enough to freeze the entire contents of the ditches in winter, it would not be expedient to draw off the water in the autumn, as the presence of so large a quantity of ice in the soil might prove injurious to trees too young and small to shelter the ground effectually against frost.

Chevandier computes that, if the annual growth of the pine in the marshy and too humid soil of the Vosges be represented by one, it will equal two in ordinary dry ground, four or five on slopes so ditched or graded as to retain the water flowing upon them from roads or steep declivities, and six where the earth is kept sufficiently moist by infiltration from running brooks.—Comptes Rendus a l'Academie des Sciences, t. xix., Juillet, Dec., 1844, p. 167. The effect of accidental irrigation in well shown in the growth of the trees planted along the canals of irrigation which traverse the fields in many parts of Italy. They nourish most luxuriantly, in spite of continual lopping, and yield a very important contribution to the stock of fuel for domestic use while trees, situated so far from canals as to be out of the reach of infiltration from them, are of much slower growth, under circumstances otherwise equally favorable. In other experiments of Chevandier, under better conditions, the yield of wood was increased, by judicious irrigation, in the ratio of seven to one, the profits in that of twelve to one. At the Exposition of 1855, Chambrelent exhibited young trees, which, in four years from the seed, had grown to the height of sixteen and twenty feet, and the circumference of ten and twelve inches. Chevandier experimented with various manures, and found that some of them might be profitably applied to young but not to old trees, the quantity required in the latter case being too great. Wood-ashes and the refuse of soda factories are particularly recommended. See, on the manuring of trees, Chevandier, Recherches sur l'emploi de divers amendements, etc., Paris, 1852, and Koderle, Grundsatze der Kunstlichen Dungung im Forstculturwesen. Wien, 1865.

I have seen an extraordinary growth produced in fir-trees by the application of soapsuds; in a young and sickly cherry-tree, by heaping the chips and dust from a marble-quarry, to the height of two or three feet, over the roots and around the stem; and cases have come to my knowledge where like results followed the planting of vines and trees in holes half filled with fragments of plaster-castings, and mortar from old buildings. Chevandier's experiments in the irrigation of the forest would not have been a "new thing under the sun" to wise King Solomon, for that monarch saya: "I made me pools of water, to water therewith, the wood that bringeth forth trees." Eccles. ii. 6.]

When the forest is approaching maturity, the original processes already described are repeated; and as, in different parts of an extensive forest, they would take place at different times in different zones, it would afford indefinitely an annual crop of small wood, fuel, and timber.

The duties of the forester do not end here, for it sometimes happens that the glades left by felling the older trees are not sufficiently seeded, or that the species, or essences, as the French oddly call them, are not duly proportioned in the new crop. In this case, seed must be artificially sown, or young trees planted in the vacancies. Besides this, all trees, whether grown for fruit, for fuel, or for timber, require more or less training in order to yield the best returns. The experiments of the Vicomte de Courval in sylviculture throw much light on this subject, and show, in a most interesting way, the importance of pruning forest-trees. The principal feature of De Courval's very successful method is a systematical mode of trimming which compels the tree to develop the stem, by reducing the lateral ramification. Beginning with young trees, the buds are rubbed off from the stems, and superfluous lateral shoots are pruned down to the trunk. When large trees are taken in hand, branches which can be spared, and whose removal is necessary to obtain a proper length of stem, are very smoothly cut off quite close to the trunk, and the exposed surface is IMMEDIATELY brushed over with mineral-coal tar. When thus treated, it is said that the healing of the wound is perfect, and without any decay of the tree. Trees trained by De Courval's method, which is now universally approved and much practised in France, rapidly attained a great height. They grow with remarkable straightness of stem and of grain, and their timber commands the highest price. [Footnote: See De Courval, Taille et conduite des Arbres forestieres et autres arbres de grande dimension. Paris, 1861.

The most important part of Viscount de Courval's system will be found in L'Elagage des Arbres, par le Comte A. Des Cars, an admirable little treatise, of which numerous editions, at the price of one franc, have been printed since the first, of 1864, and which ought to be translated and published without delay in the United States.]

A system of plantation, specially though not exclusively suited to very moist soils, recommended by Duhamel a hundred years ago, has been revived in Germany, within about twenty years, with much success. It is called hill-planting, and consists in placing the young tree upright on the greensward with its roots properly spread out, and then covering the roots and supporting the trunk by thick sods cut so as to form a circular hillock around it. [Footnote: See Manteuffel, L'Art de Planter, traduit par Stumper. Paris, 1868.] By this method it is alleged trees can be grown advantageously both in dry ground and on humid soils, where they would not strike root if planted in holes after the usual mauner. If there is any truth in the theory of a desiccating action in evergreen trees, plantations of this sort might have a value as drainers of lands not easily laid dry by other processes. There is much ground on the great prairies of the West, where experiments with this method of planting are strongly to be recommended.

It is common in Europe to permit the removal of the fallen leaves and fragments of bark and branches with which the forest-soil is covered, and sometimes the cutting of the lower twigs of evergreens. The leaves and twigs are principally used as litter for cattle, and finally as manure, the bark and wind-fallen branches as fuel. By long usage, sometimes by express grant, this privilege has become a vested right of the population in the neighborhood of many public and even large private forests; but it is generally regarded as a serious evil. To remove the leaves and fallen twigs is to withdraw much of the pabulum upon which the tree was destined to feed. The small branches and leaves are the parts of the tree which yield the largest proportion of ashes on combustion, and of course they supply a great amount of nutriment for the young shoots. "A cubic foot of twigs," says Vaupell, "yields four times as much ashes as a cubic foot of stem wood. … For every hundred weight of dried leaves carried off from a beech forest, we sacrifice a hundred and sixty cubic feet of wood. The leaves and the mosses are a substitute, not only for manure, but for ploughing. The carbonic acid given out by decaying leaves, when taken up by water, serves to dissolve the mineral constituents of the soil, and is particularly active in disintegrating feldspar and the clay derived from its decomposition. … The leaves belong to the soil. Without them it cannot preserve its fertility, and cannot furnish nutriment to the beech. The trees languish, produce seed incapable of germination, and the spontaneous self-sowing, which is an indispensable element in the best systems of sylviculture, fails altogether in the bared and impoverished soil." [Footnote: Vaupell, Bogens Indvandring i de Danske Skove, pp. 29, 46. Vaupell further observes, on the page last quoted: "The removal of leaves is injurious to the forest, not only because it retards the growth of trees, but still more because it disqualifies the soil for the production of particular species. When the beech languishes, and the development of its branches is less vigorous and its crown less spreading, it becomes unable to resist the encroachments of the fir. This latter tree thrives in an inferior soil, and being no longer stifled by the thick foliage of the beech, it spreads gradually through the wood, while the beech retreats before it and finally perishes."

Schleiden confirms the opinion of Vaupell, and adds many important observations on this subject.—Fur Baum und Wald, pp. 64, 65.]