The Earth as Modified by Human Action

by George P. Marsh

The successive changes in the spontaneous growth of the forest, as proved by the character of a wood found in bogs, are such as to have suggested the theory of a considerable change of the climate during the human period. But this theory cannot be admitted upon the evidence in question. In fact, the order of succession—for a rotation or alternation is neither proved nor probable—may be made to move in opposite directions in different countries with the same climate and at the same time. Thus in Denmark and in Holland the spike-leaved firs have given place to the broad-leaved beech, while in Northern Germany the process has been reversed, and evergreens have supplanted the oaks and birches of deciduous foliage. The principal determining cause seems to be the influence of light upon the germination of the seeds and the growth of the young tree. In a forest of firs, for instance, the distribution of the light and shade, to the influence of which seeds and shoots are exposed, is by no means the same as in a wood of beeches or of oaks, and hence the growth of different species will be stimulated in the two forests.

When ground is laid bare both of trees and of vegetable mould, and left to the action of unaided and unobstructed nature, she first propagates trees which germinate and grow only under the influence of a full supply of light and air, and then, in succession, other species, according to their ability to bear the shade and their demand for more abundant nutriment. In Northern Europe the large, the white birch, the aspen, first appear; then follow the maple, the alder, the ash, the fir; then the oak and the linden; and then the beech. The trees called by these respective names in the United States are not specifically the same as their European namesakes, nor are they always even the equivalents of these latter, and therefore the order of succession in America would not be precisely as indicated by the foregoing list, but, so far as is known, it nevertheless very nearly corresponds to it.

It is thought important to encourage the growth of the beech in Denmark and Northern Germany, because it upon the whole yields better returns than other trees, and does not exhaust, but on the contrary enriches, the soil; for by shedding its leaves it returns to it most of the nutriment it has drawn from it, and at the same time furnishes a solvent which aids materially in the decomposition of its mineral constituents.

When the forest is left to itself, the order of succession is constant, and its occasional inversion is always explicable by some human interference. It is curious that the trees which require most light are content with the poorest soils, and vice versa. The trees which first appear are also those which propagate themselves farthest to the north. The birch, the larch, and the fir bear a severer climate than the oak, the oak than the beech. "These parallelisms," says Vaupell, "are very interesting, because, though they are entirely independent of each other," they all prescribe the same order of succession.—Bogens Indvandring, p. 42. See alo Berg, Das Verdrangen der Laubralder im Nordlichen Deutschland, 1844. Heyer, Das Verhalten der Waldbaume gegen Licht und Schatten, 1852. Staring, De Bodem van Nederland, 1856, i., pp. 120-200. Vaupell, De Danske Skove, 1863. Knorr, Studien uber die Buchen-Wirthschaft, 1863. A. Maury, Les Forets de la Gaule, pp. 73, 74, 377, 384.]

Another evil, sometimes of serious magnitude, which attends the operations of the lumberman, is the injury to the banks of rivers from the practice of floating. I do not here allude to rafts, which, being under the control of those who navigate them, may be so guided as to avoid damage to the shore, but to masts, logs, and other pieces of timber singly entrusted to the streams, to be conveyed by their currents to sawmill ponds, or to convenient places for collecting them into rafts. The lumbermen usually haul the timber to the banks of the rivers in the winter, and when the spring floods swell the streams and break up the ice, they roll the logs into the water, leaving them to float down to their destination. If the transporting stream is too small to furnish a sufficient channel for this rude navigation, it is sometimes dammed up, and the timber collected in the pond thus formed above the dam. When the pond is full, a sluice is opened, or the dam is blown up or otherwise suddenly broken, and the whole mass of lumber above it is hurried down with the rolling flood. Both of these modes of proceeding expose the banks of the rivers employed as channels of flotation to abrasion, [Footnote: Caimi states that "a single flotation in the Valtelline, in 1830, caused damages appraised at $250,000."—Cenni sulla Importanza e Coltura dei Boschi, p. 65.] and in some of the American States it has been found necessary to protect, by special legislation, the lands through which they flow from the serious injury sometimes received through the practices I have described. [Footnote: Many physicists who have investigated the laws of natural hydraulics maintain that, in consequence of direct obstruction and frictional resistance to the flow of the water of rivers along their banks, there is both an increased rapidity of current and an elevation of the water in the middle of the channel, so that a river presents always a convex surface. Others have thought that the acknowledged greater swiftness of the central current must produce a depression in that part of the stream. The lumbermen affirm that, while rivers are rising, the water is highest in the middle of the channel, and tends to throw floating objects shorewards; while they are falling, it is lowest in the middle, and floating objects incline towards the centre. Logs, they say, rolled into the water during the rise, are very apt to lodge on the banks, while those set afloat during the falling of the waters keep in the current, and are carried without hindrance to their destination, and this law, which has been a matter of familiar observation among woodmen for generations, is now admitted as a scientific truth.

Foresters and lumbermen, like sailors and other persons whose daily occupations bring them into contact, and often into conflict, with great natural forces, have many peculiar opinions, not to say superstitious. In one of these categories we must rank the universal belief of lumbermen, that with a given head of water, and in a given number of hours, a sawmill cuts more lumber by night than by day. Having been personally interested in several sawmills, been assured by them that their uniform experiences established the fact that, other things being equal, the action of the machinery of sawmills is more rapid by night than by day. I am sorry—perhaps I ought to be ashamed—to say that my skepticism has been too strong to allow me to avail myself of my ooportunites of testing this question by passing a night, watch in hand, counting the strokes of a millisaw. More unprejudiced, and, I must add, very intelligent and credible persons have informed me that they have done so, and found the report of the sawyers abundantly confirmed. A land surveyor, who was also an experienced lumberman, sawyer, and machinist, a good mathematician, and an accurate observer, has repeatedly told me that he had very often "timed" sawmills, and before the difference in favor of night-work above thirty per cent. Sed quaere.]

Restoration of the Forest.

In most countries of Europe—and I fear in many parts of the United States—the woods are already so nearly extirpated, that the mere protection of those which now exist is by no means an adequate security against a great increase of the evils which have already resulted from the diminution of them. Besides this, experience has shown that where the destruction of the woods has been carried beyond a certain point, no coercive legislation can absolutely secure the permanence of the remainder, especially if it is held by private hands. The creation of new forests, therefore, is generally recognized, wherever the subject has received the attention it merits, as an indispensable measure of sound public economy. Enlightened individuals in some European states, the Governments in others, have made extensive plantations, and France, particularly, has now set herself energetically at work to restore the woods in her southern provinces, and thereby to prevent the utter depopulation and waste with which that once fertile soil and genial climate are threatened.

The objects of the restoration of the forest are as multifarious as the motives that have led to its destruction, and as the evils which that destruction has occasioned. It is hoped that the replanting of the mountain slopes, and of bleak and infertile plains, will diminish the frequency and violence of river inundations, prevent the formation of new torrents and check the violence of those already existing, mitigate the extremes of atmospheric temperature, humidity, and precipitation, restore dried-up springs, rivulets, and sources of irrigation, shelter the fields from chilling and from parching winds, arrest the spread of miasmatic effluvia, and, finally, furnish a self-renewing and inexhaustible supply of a material indispensable to so many purposes of domestic comfort, and to the successful exercise of every art of peace, every destructive energy of war. [Footnote: The preservation of the woods on the former eastern frontier of France, as a kind of natural abattis, was recognized by the Government of that country as an important measure of military defence, though there have been conflicting opinions on the subject.]

The Economy of the Forest.