Popular Science Monthly/Volume 11/August 1877/The Climatic Influence of Vegetation-A Plea for our Forests
THE
POPULAR SCIENCE
MONTHLY.
AUGUST, 1877.
| THE CLIMATIC INFLUENCE OF VEGETATION.—A PLEA FOR OUR FORESTS. |
By F. L. OSWALD, M.D.
"AS a fellow Unitarian, I feel sorry for the Turks," Dr. Schliemann writes from Salonica, "but, as a respecter of God's physical laws, I must own that they deserve their fate. Men who for twenty generations have proved themselves tree-destroyers on principle, have no right to complain if the world rises against them."
It would be well for the world if for the last twenty generations the Turks had been the only "tree-destroyers on principle." Since the advent of the Christian religion, the physical history of our planet records the steady growth of a desert, which made its first appearance on the dry table-land of Southern Syria, and gradually spreading eastward down the Euphrates toward Afghanistan, and westward along both shores of the Mediterranean, now extends from Eastern Persia to the western extremity of Portugal, and sends its harbingers into Southern France and the southeastern provinces of European Russia. Like a virulent cancer, the azoic sand-drifts of the Moab Desert have eaten their way into Southern Europe and Northern Africa, and dried up the life-springs of districts which beyond all dispute were once the garden-regions of this earth.
Prince de Ligne, countryman and contemporary of Maria Theresa, wrote an essay "On the Location of the Earthly Paradise," and, after some reflections on the hygienic influence of different climates, calls attention to the fact that "paradise-traditions, in locating the garden of Eden, differ only in regard to longitude, but not to latitude. The latitude keeps always near the snow-boundary, a line just south of the regions where snow may fall, but will not stay on the ground. It passes through Thibet, Cashmere, Northern Persia, and Asia Minor, and reaches the meridian of Europe near the centre of the Mediterranean." The nations that "celebrated life as a festival" have lived along this line, and we may doubt if in the most favored regions of the New World human industry, with all the aids of modern science, will ever reunite the opportunities of happiness which Nature once lavished on lands that now entail only misery on their cultivators. All over Spain and Portugal, Southern Italy, Greece, Turkey, Asia Minor, Persia, and Western Afghanistan, and throughout Northern Africa, from Morocco to the valley of the Nile, the aridity of the soil makes the struggle for existence so hard that to the vast majority of the inhabitants life from a blessing has been converted into a curse.
Southern Spain, from Gibraltar to the head-waters of the Tagus, maintains now only about one-tenth of its former population, Greece about one-twentieth. As late as a. d. 670, a good while after the rise of the Mohammedan power, the country now known as Tripoli, and distinct from the Sahara only through the elevation of its mountains, was the seat of eighty-five Christian bishops, and had a population of 6,000,000, of which number three-quarters of one per cent, are now left! The climate which, according to authentic description, must once have resembled that of our Southern Alleghanies, is now so nearly intolerable that even the inhumanity of an African despot forbears to exact open-air labor from 9 a. m. to 5 p. m. Steamboats that pass near the Tripolitan coast in summer, on their way from Genoa to Cairo, have to keep up a continual shower of artificial rain to save their deck-hands from being overcome by the furnace-air that breathes from the ban-en hills of the opposite coast. The rivers of some of these countries have shrunk to the size of their former tributaries, and from Gibraltar to Samarcand the annual rainfall has decreased till failure of crops has become a chronic complaint.
And all this change is due to the insane destruction of forests. The great Caucasian sylvania that once adorned the birth-land of the white race from the Western Pyrenees to the foot-hills of the Himalayas has disappeared; of the forest-area of Italy and Spain, in the days of the elder Pliny, about two acres in a hundred are left; in Greece, hardly one. But even the nakedness of the most sterile tracts of Southern Europe is exceeded by the utter desolation of the Ottoman provinces. If there was not evidence that a great part of the ruin had been accomplished before the fall of the Byzantine Empire, the Turks would really seem to have been "tree-destroyers on principle." In the recesses of the Taurus range and the inaccessible heights of those
". . . . mountains that distill
Indus and Oxus from their icy caves"—
a few remnants of wood have survived the general devastation, but throughout the lowlands, from Bokhara to the Golden Horn, not a stick or bush can grow up before the wood-famine of the wretched population lays violent hands upon it. In Northern Africa, Dalmatia, and the larger islands of the Grecian Archipelago, the same evil has made terrible advances. The Mediterranean Sea, once a forest-lake of paradise, is now a dead sea, surrounded by dusty and burning coasts, often for hundreds of miles without a vestige of organic life.
The present appearance of the Troad, the neighborhood of Lake Tiberias, the valley of the Euphrates, and other districts that were once teeming with population, can actually make us doubt if there ever was such a thing as an original desert. On the plateau of Sidi-Belbez, in the very centre of the Sahara, Champollion traced the course of former rivers and creeks by the depressions in the soil and the shape of the smooth-washed pebbles. He also found tree-stumps, now almost petrified, and covered by a six-foot stratum of burning sand.
"And so the astounding truth dawns upon us," he says, "that this desert may once have been a region of groves and fountains, and the abode of happy millions. Is there any crime against Nature which draws down a more terrible curse than that of stripping our Mother Earth of her sylvan covering? The hand of man has produced this desert, and I verily believe every other desert on the surface of this earth. Earth was Eden once, and our misery is the punishment of our sins against the world of plants. The burning sun of the desert is the angel with the flaming sword who stands between us and paradise."
That the inhabitants of these artificial deserts have failed to recognize the cause of their misery implies a degree of infatuation and mental blindness which may appear even more incredible to future generations than the thousand years' belief in witchcraft and the patient submission of 80,000,000 able-bodied men to a juggler-guild of priests. Even frogs and fishes become uneasy if the plug-hole of their tank is opened and their life-element begins to ebb away; and it should be supposed that, without any scientific aids to reflection, the sheer instinct of self-preservation could have suggested the simple remedy before the evil attained its present proportions.
But this blindness of the Latin races and the devotees of Islam, if not justified, is at least partly explained by the fatalism of their religion. Their belief in supernatural agencies, and a meddlesome Providence that ruled the world in spite of man, naturally produced indifference to all physical sciences whatever. The three Semitic religions have done more to divorce man from Nature than all his inborn vices and the "necessary decay of civilized races" that is so often preferred as an explanation. "Though our mortal eyes have failed to penetrate the depths of heaven," says Erasmus, "we have succeeded in losing sight of our own earth." If this earth was a vale of tears, and heaven our proper home, all attention to earthly affairs seemed so much lost time, and in the souls of men who were taught to consider their natural feelings as antagonistic to the will of God the warning voice of instinct was raised in vain.
Much more unaccountable seems our own indifference to the disappearance of our forests, since our science has demonstrated to the satisfaction of all rational and semi-rational beings—including some very conservative rulers of Western Europe—that an animal flayed, or a tree stripped of its bark, does not perish more surely than a land deprived of its trees.
The Duke of Burgundy's rule, "One-third to the hunter, two-thirds to the husbandman," expresses about the most desirable proportion of woodlands and cultivated fields. In a country blessed with such a plethora of woods as the United Stales between the Atlantic and the valley of the Mississippi could boast of less than a hundred years ago, the work of "clearing" could therefore be pursued within very liberal limits, not only without injury, but with positive benefit to the climate, inasmuch as it would counteract excess of moisture and miasmatic tendencies. But in some of our Southern and Central States this limit has already been passed. The States of Ohio and Indiana, and the southern parts of Kentucky and Michigan, so recently a part of the great East-American forest, have even now a greater percentage of treeless area than Austria and the North-German Empire, that have been settled and cultivated for upward of a thousand years. The northern borders of Ohio are kept comparatively fertile by the neighborhood of the great lakes, but the central regions, and many of the river-counties, begin to suffer from drought, and see their springs fail in every summer. The "Blue-Grass" region of Kentucky, once the pride of the West, has now districts of such a barren and arid nature that their stock-farmers are moving toward the Cumberland Mountains, because the creeks and old springs dried up, and their wells became too low to furnish water for their cattle.
Wherever tobacco and cotton are cultivated, the work of ruin has made rapid advances, and in all the southeastern counties of Virginia and North Carolina, and throughout Mississippi, Alabama, Georgia, and South Carolina, the traveler may ride for hours without seeing more than four or five trees in a group; droughts are becoming more and more frequent, and the locust, that ominous pioneer of the desert, has made its appearance.
The climatic influence of arboreal vegetation must be more generally understood, before such legislative measures as the importance of the subject demands, can be hoped for. In the economy of Nature forests perform innumerable functions which no artificial contrivance can imitate, and of which the following are only the most important:
Woods, in the first place, are the water-reservoirs of Nature, and hold in the network of their roots and their moss-carpet the moisture which is intended to supply our water-courses in the season of midsummer heat. One acre of full-grown beech-trees absorbs and dispenses as much humidity as twenty acres of grape-vines and tobacco, and more than two hundred acres of cereals.
Forests produce rain. Under the influence of vertical sun-rays trees exhale the aqueous vapors which their leaves have absorbed from the atmosphere, and in contact with the night-air or any stray current of lower temperature, these vapors discharge rain-showers even in midsummer, and at a great distance from the sea.
By moistening the air woodlands also moderate the extremes of heat and cold. It is seen on the sea-shore how beneficently humidity operates in allaying the severity of winter, and in summer the evaporation of dew and rain gives us cool breezes when they are most needed. By the extirpation of forests the climate of the entire Orbis Romanus has been changed from the summer temperature of West Virginia to the furnace-heat of New Mexico and Arizona.
Besides this, the forest by shade in summer and fuel in winter protects us directly against the vicissitudes of temperature, and at the foot of high mountains interposes a mechanical barrier between the valleys and avalanches in the north, and floods in the south. The water-torrents, which not only flood and damage the lowlands, but carry their fertile soil away, are imbibed or detained by extensive forests. Joseph II. of Austria was right to attach heavy penalties to the destruction of the "Bannwälder," the woods on the Alpine slopes, that protect the valleys from avalanches, and to propose that in wars, even à l'outrance, the trees of a country should be spared by international agreement.
Our woods are also the home and shelter of those best friends of man, the insectivorous birds. A country destitute of trees is avoided by birds, and left to the ravages of locusts and other insects, which, as we saw on our own continent, always attack the barren and naked districts. Our locust-swarms devastated the "Great West," i. e., the treeless expanse between the Mississippi and the Rocky Mountains, but spared the woodlands of the Alleghanies and the timber-regions of the Pacific slope.
The exhilarating influence of a woodland excursion is not altogether due to scenic effects and imagination. Forests exhale oxygen, the life-air of flames and animal lungs, and absorb or neutralize a variety of noxious gases. Scirrhous affections of the skin and other diseases disappear under the disinfecting influence of forest-air. Dr. Brehm observes that ophthalmia and leprosy, which have become hereditary diseases, not only in the valley of the Nile, but also on the table-lands of Barca and Tripoli, are utterly unknown in the well-timbered valley of Abyssinia, though the Abyssinians live more than a hundred geographical miles nearer to the equator than their afflicted neighbors.
The traditions of the "blessed islands of the West," the "Garden of the Hesperides," probably referred to Madeira and the Cape-Verde Archipelago, which, according to De Gama's description, must have come nearer to our idea of terrestrial paradise than any other region of this earth. "The ills that flesh here is heir to," he says, "are only three: wounds, the effects of poison, and decrepitude—the latter rarely makes its appearance before the completion of the ninetieth year." Since the Portuguese have felled their glorious forests for the sake of madeira (building-material), these islands have become hotbeds of disease.
The valley of the Guadalquivir, as late as a century before the discovery of America, supported a population of 7,000,000 of probably the healthiest and happiest men of Southern Europe. Since the live oak and chestnut groves of the surrounding heights have disappeared this population has shrunk to a million and a quarter of sickly wretches, who depend for their sustenance on the scant produce of sandy barrens that become sandier and drier from year to year.
It would be exaggeration to say that the barrenness of a treeless country is an evil without remedy. Nature is always ready to assist in any work of regeneration, and there is no desert so void and naked that it might not be reclaimed in the course of half a century. The Khédive of Egypt has wrested land from the sand-wastes as the Hollanders win it from the sea, and by a cheaper process than the building of extensive dikes. By planting date-palms and olive-trees, Egypt has added many hundred square miles to her arable surface, and, as Baker-Pasha assures us, her annual rainfall has almost doubled. Between Karnak and Soodan the rain-gauge shows now a yearly average of sixteen inches, where nine inches was the maximum before 1820. And not only the limits of these tree-plantations, but also the adjoining districts, have been benefited; on the table-land of Wady-Halfa the present temperature is not nearly as oppressive as it was within the memory of men now living, and currant-bushes and wild-mulberries have sprung up where they never grew before. In France, too, the Government has reclaimed the Landes, a sandy steppe on the southwestern coast, by planting willows and bay-trees; and even Algeria has been improved by the persistent tree-culture of the French colonists.
But how slow and laborious is this work of restoration, and how easily might we forestall its necessity if we would begin in time! A legislative act to protect the woods of all the upper ridges in hill countries, and of a certain percentage of acres, say fifteen in a hundred, in the plains, would be an effectual guarantee against evils which otherwise will assuredly overtake us, and speedier than Europe, on account of the compact shape of our continent, that deprives us of the advantages of a marine climate.
Let us remember that the aphorism of the greatest physician of modern times applies to other organisms as well as to the human body. "Timely prevention," said Dr. Radcliffe, "not only saves us from diseases, but from those greater evils—the remedies."