The Effect of Trees on Humidity, Evaporation, Rainfall, and Prevailing "Winds. —Nebraska's Generous Labor in Behalf of the Reproduction of Trees, and her Reward. — Humidifying Influence of the Pacific Winds on Iowa, Illinois, and Wisconsin.—The Humidity of Forests, to What Due.—The Theory of Condensation in Connection with Trees. —Evil Results of Forest Destruction in Santa Cruz. — The Serious Results of Forest Destruction to Manufacturing Industries. — The Tree-planting of Lower Egypt and Consequent Rainfall.—Moisture Distribution of Kansas and Nebraska, to What Due. — The Agricultural Benefits Derived from Tree-planting in Australia. — The Australian Desert's Reclamation Possible. — The Destruction of Forest-lands for Agricultural Purposes in the United States. —Decrease of Lumber Supply and its Increasing Value. — Precautionary Measures Discussed.
The effect of trees upon the rainfall of a country is no longer disputed by the intelligent. A good-sized peach-tree will give off eighteen pounds, or about two gallons, of moisture every twelve hours. The evaporation of the earth through trees is immense; the roots often draw from springs themselves, and throw off through their branches great volumes of humid air.
Those who have watched the effect of forests on rainfall say that, by commencing at the edge of any dry belt, the forests, and consequent rainfall, may gradually be extended across the whole of the dry belt. The experiment is being tried in Nebraska, and I believe with encouraging results, as the rainfall is gradually increasing. No state in the Union has done more to replace her forests, and I am happy to say Nebraska is already reaping the rewards of her generous labor in behalf of the trees.
At a depth of some twenty feet from the surface of the earth white sand is struck in both Kansas and Nebraska, which is full of water, and in some places forms subterranean streams. This makes both these states famous forest-growing regions, as the roots of the trees readily seek the moist white sand, and the trees grow with a rapidity which is perfectly astonishing.
I think the great currents of air which leave the Pacific coast humid and warm are forced up by the high mountains until they become cold, and are discharged in snows in the Pocky Mountains, when, leaving the mountains dry, they sweep over the great plains, finding no moisture to take up until they cross the Missouri and Mississippi, when, having been recharged, they empty in Iowa, Illinois, and "Wisconsin. "We know that in "Wyoming Territory the dearth is almost complete, and the dry winds blow incessantly. But in Nebraska the heavily timbered heads of her streams give some humidity, and the clouds empty in frequent showers along the Loups, Niobrara, Plattes, Elkhorn, and Missouri. In time, as Nebraska increases her forests, the rains will become more frequent, and some day, should she persist in her present system of tree-planting, she will be as well watered as Iowa, Illinois, "Wisconsin, or states farther east.
Every one has noticed the moisture of the soil in a wood. There is as much difference between the soil under trees and that on a barren hill-top as there is in the temperature of a well and an open plain. The humidity of a forest is due to the discharge of moisture through the leaves of the trees. It is this peculiarity which keeps a stream strong and full where it flows for a long distance through woods; not only do the trees shade the stream from the rays of the sun and prevent evaporation, but they keep its banks moist and soft, and, instead of drinking up the stream, frequently contribute to its waters. The Elbe has lost eighteen per cent, of its flow in consequence of cutting away the trees along its banks, exposing its waters to the hot sun.
The island of Santa Cruz, in the "West Indies, which twenty-five or thirty years ago was a garden, is now almost a desert in consequence of cutting away the forests. The theory is that the dry currents of air are retarded by forests, and elevated until a point of condensation is reached. Radiation is also prevented, the air cooled, and the clouds, passing over trees, are rendered more easily condensed. Electricity is also a great agent, the trees being negatively charged, and drawing with great power the positively charged clouds. This theory ' is no longer a matter of doubt or experiment, but a fact demonstrated by experience and a knowledge of the laws that govern the atmosphere.
But not only in Europe, but in America, is the loss of timber already lamentably felt. Many of our rivers have lost half their usefulness for manufacturing purposes. The Connecticut is hardly navigable, and the? Kennebec and Merrimac have shrunk one fourth. The; Potomac has lost nearly one fourth of its volume, andj the Hudson declined a sixth. If the Adirondack wilderness and other forests adjacent were destroyed it would probably, in time, render the Hudson wholly unnavi-gable.
As has been explained, forests are vast reservoirs of humidity—lessening the dryness of the surrounding atmosphere, and aiding the perennial flow of springs and streams. Says Bryant, " instances are on record of the drying up of springs and rivulets when the woods which shaded them were felled, and of their reappearance when the trees were suffered again to grow."
The increase of rainfall in Lower Egypt since the formation of extensive plantations of trees is proof of their effect upon the rainfall of a country. In 1869 there were fourteen rainy days at the Isthmus of Suez, where rain had rarely if ever before been known, and the cause was ascribed to the planting of large plantations of trees. In Kansas and Nebraska the rains are much more evenly distributed through the seasons than they used to be, and this is undoubtedly due to the stirring of the soil and the planting of trees. A similar change has been noticed in Colorado, where the flow of small streams, it is said, is becoming stronger and more permanent. The waters of the Great Salt Lake, which some years ago seemed to be receding, have again risen, and are every year increasing, as the Mormons open up farms and plant orchards in the Salt Lake valley.
The effect of forests on a country may be set down as follows: First, great humidity of the atmosphere. Second, more rapid evaporation. Third, greater regularity of rainfall. Fourth, diminished force of the prevailing winds. In no country has the effect of settlement on the climate been more apparent than in Australia. Keeping sheep there is in many places no longer as profitable as it used to be; but, on the other hand, large tracts of land that were worthless before have latterly become fit for agriculture. There has been a decided increase of forests and a consequent increase of moisture in many parts, giving hopes that eventually the whole interior desert may be reclaimed. The direct effect of sheep-raising "has been to keep down the long grass which formerly afforded material for destructive fires. The trees, young and old, had been periodically burned by these fires, until the country, becoming almost treeless, its climate had been rendered arid and its soil sterile. If the climate in Australia can be changed and rains made to fall by the growing of timber, why not our own country? And why may not our plains, in time, become well-watered regions and good farming countries ?
Incredible as it may seem, it is nevertheless true that forests are still felled and burned for the purpose of bringing the land they stand upon under cultivation. From 1860 to 1870 no less than twelve million acres of forest were cut, the timber logged and burned on the ground, so that the land could be farmed. The annual decrease of forests by logging and burning is still, I am told, some eight hundred thousand acres per year. And while we are thus destroying our timber by every possible means, and taking no adequate steps for replacing it, the demand for lumber is increasing at the rate of twenty-five per cent, per annum. I cannot say what is just the annual decrease of our forests, but it cannot be less than eight million acres per annum, while as yet we do not plant more than a tenth of that amount in new timber, outside of Nebraska.
That we have shamefully and wantonly destroyed our forests no right - thinking man will deny. "We cannot undo the past, but we may still provide for the future if we set to work with diligence and sense, and earnestly persevere. What, then, should be done? Let every man remember when he fells a big tree he is doing something which he cannot undo, and destroying that which in his lifetime he cannot replace, and let him cut down just as few trees as possible. Farmers should plant hedges around their fields, and avoid cutting down timber for rails or fencing of any kind. Division fences between farms ought always to be made of hedges. Strong herd-laws should be passed in the states and territories, and stock not be allowed to run at large, thus doing away with the necessity of so many fences. Millions of dead capital in the states might thus be utilized and brought into use for other purposes. States should make liberal appropriations, and foster and encourage in every way the replanting of forests. Nebraska has admirable herd and forestry laws, and may be taken as a model in this respect by her sister states. Congress should enact strong laws for the protection of timber on the public domain, or turn it over to the states and territories. If placed under the War Department it would be protected, l Overseers of roads should be made to plant trees along the highways at the public expense. Railways should be compelled to plant trees along the whole length of their track on either side, and preserve them from fires. Reservations should be laid off around the heads of rivers and streams, and no timber be allowed to be cut there. It is true that we cannot in one or even two generations repair all the damage that has already been done; but, by beginning at once, we may yet avoid the terrible scourge of a timber famine in the United States.