Popular Science Monthly/Volume 2/December 1872/Forests and Fruit-Growing
|FORESTS AND FRUIT-GROWING.|
FRUIT has become a necessary of life—a great variety of fruit indeed, and a great deal of it; and this will become more and more the case with the increase of intelligence and thrift. The great abundance of most kinds of fruit for the last two or three years may cause us to feel a security, which is not well grounded, with regard to the conditions of climate necessary to the unfailing production of fruit. Only within a few years past have there been seasons when the fruit-crop was very light, and not at all adequate to the demand. One of the causes of this is the capriciousness of the seasons, and this capriciousness, I believe, is becoming constantly greater as the country grows older.
An inquiry, then, of much scientific interest, and of great material importance, has reference to what may be the cause of this increasing uncertainty of the fruit crop. In the early settlement of the country, it was easy to grow peaches, even in localities where growing peaches now seldom gladden the eye. In Ohio between the parallels of 40° and 41°, for example, peach-buds were seldom injured by winter or spring frosts, and the crop was abundant almost every year when the country was "new." For the last twenty-five years peaches miss oftener than they hit, and in many parts this has told so fearfully against the enterprise of production that scarcely a peach-tree is now to be seen.
The clearing of the country had made this change. The continued clearing of the country will increase the mischief still more. The growing of peaches and of most other fruits will be driven, as indeed it already has been, to special localities and special soils. It is now for such localities to look out in time and preserve as far as possible the favorable conditions they now have, and if possible to increase them.
More especial reference is here had to that part of our country which lies north of the fortieth parallel, where most of the fruit-localities are to be found in the vicinity of considerable bodies of water.
The water absorbs heat during the summer, which it slowly gives off on the approach of cold weather, warming the atmosphere in its vicinity, and preventing the occurrence of early frosts in the fall along the shore-border from five to ten miles wide. This gives the wood and buds a chance to mature thoroughly, so that they will endure a harder freeze in the winter than wood and buds which were suddenly stopped in the course of maturing by an early frost in the fall. In the spring the waters warm more slowly than the land, and the atmosphere thus chilled along this same shore-belt keeps back vegetation and fruit-buds so as greatly to lessen the danger from late frosts; and what may seem to be a contradiction, but is nevertheless true, spring frosts are usually lighter within than they are outside this shore-belt.
These several advantages from the proximity of a considerable body of water are well understood. There is another, however, that may be of some value. During the heated term of summer there is always a cool breeze from the water which modifies the temperature of the hottest part of the day along this otherwise favored border of shore-land, and may act beneficially in various ways: first, by promoting a more active circulation of air among the leaves and young branches, thereby favoring the healthy action of the organic surfaces—hence, greater immunity from blight and mildew in this region; secondly, by affording protection against the injury to which growing fruit is liable from excessive heat; thirdly, by maintaining a greater uniformity of heat between night and day. The experiments of Köppen have shown that change of temperature alone is deleterious to vegetable growth; and we may, perhaps, justly infer that uniformity of temperature, when it lies at or near that degree which is most favorable to healthy vegetable activity, is a desirable point in a fruit-growing climate for the even, early, and better maturing of fruit.
The influence of forests on rainfall is still an unsettled question. It is a very general impression that forests, in some way, promote the fall of rain when it would not occur if the same region was bare of trees. A great array of authorities may be quoted in favor of this view. It is believed that Spain, parts of France, Switzerland, and the Tyrol, Northern Africa, Persia and Palestine, Egypt and India, the islands Malta and Mauritius, the Cape Verd Islands, and most of the West Indies, have either been turned into deserts or greatly injured by the destruction of their forests, and the blight and droughts which have followed. It is alleged, too, that the planting of forests has in some instances, as in Scotland, Egypt, and St. Helena, caused a more abundant rainfall. But these alleged results, though supported by great names in science, are disputed. Forests may affect rainfall for any thing positively known, but the evidence that they do so is not such as science can accept. But, however this may be, they have doubtless much to do with the benefit which vegetation receives from the rain that does fall.
In a country quite destitute of timber the surface would dry off much more quickly, in consequence of the free sweep afforded to the winds. The water from rains would also pass over the surface more freely into the brooks, and be thus lost to vegetation. The spongy surface of the forest absorbs a larger proportion of rain than the open fields, and thus retains it in the soil as a source from which the neighboring streams receive a continual supply, while its evaporation from the surface and its transpiration through the leaves of the trees afford moisture to the atmosphere.
The moisture thus imparted to the atmosphere mitigates the severity of a drought in various ways: First, by lessening evaporation from the surface, as this is accelerated by a dry atmosphere, and retarded by a moist one; secondly, by affording to the soil a greater proportion of moisture for condensation, when the surface cools at night. Thirdly, by affording moisture for direct absorption by the leaves. This is a disputed point among men of science; but the late researches of Cailletet promise a reconciliation of the conflicting views, as usual, by showing that both were wrong and both right. He found that, when a plant was abundantly supplied with moisture in the soil, the leaves never absorb; but that they do absorb whenever the soil is deficient in moisture, and the leaves begin to droop.
Hence, there might be evidence of drought in a country without forests, while there were no such evidences in a country sufficiently guarded by forests, though the amount of rain had been the same in both.
These considerations are not altogether without value in regard to fruit-growing. It is true that grapes do best in rather a dry climate; but most kinds of fruit require considerable moisture, especially at the time of transplanting, and also when the fruit is maturing. In affording some mitigation of the extreme effects of dry weather, forests may be regarded as having a beneficial influence on the growing of most fruits.
Of far greater concern to the fruit-interests of any locality is the influence of woodland on temperature. On this subject there is quite a general unanimity of opinion. Certain forms of the evidence are so familiar that the conviction produced is general. Every one, who has travelled through woodlands and open fields during cold weather, has readily perceived how much warmer was the atmosphere of the wood than that of the field. It is said that engineers on our railroads find that it requires less fuel to keep up steam in passing through a long stretch of woodland (Marsh). But the warming influence of the forest has been subjected to more rigid tests than these. Boussingault proved that, within several parallels of the equator on either side, the temperature of cleared land is about two degrees higher than that which is covered with forest. But we are more directly concerned with results in our temperate climate.
The researches of Becquerel, Krutsch, and Berger, had appeared to prove, first, that a wooded region would have a cooler summer and a warmer winter than a region almost destitute of woods; and, secondly, that during the daytime the temperature of the atmosphere in the forest would always be lower, and during the night always higher, than in the open field; the difference between the diurnal maximum and minimum of the forest being less than that of the field; in other words, the diurnal temperature is more uniform.
But this is a matter involving such complicated and varying conditions, that absolute propositions are open to question, however true they may be with proper qualifications. Rivoli has very recently done much to make our knowledge of this subject definite. His observations were carefully made, under circumstances which eliminated, as much as possible, all disturbing conditions; there being no body of water near, the country level, and the wind having a fair sweep in all directions. We will state the results of his investigations as briefly as possible.
Influence of Forests on Winter Temperature.—In the winter-time, the simplest relations of the forest to temperature prevail. During this season of the year, when the wind passes into the north and becomes colder, the forest warms it; when it passes into the south and becomes warmer, the forest cools it. During winter the forest plays the role of a bad conductor, and acts as an equalizer of temperature.
Influence of Forests on Summer Temperature.—In summer the case is not so simple, owing to evaporation from the surface, transpiration through the leaves, and radiation from them. At this season of the year the atmosphere in the forest is usually warmer during the nights and colder during the day than in the open field. The night is warmer in consequence of the obstruction which the mass of foliage presents to radiation from the surface beneath it; the day is cooler in consequence of the transpiration of vapor from the leaves, and the obstruction interposed between the surface and the direct rays of the sun. In the summer, as well as in the winter, the forest usually acts as an equalizer of the temperature of the atmosphere.
While, however, this is usually the case, there are exceptions. During nights when it is calm, radiation from the leaves of the trees may cool particles of air, which, descending toward the surface, form just before daybreak a stratum of the atmosphere below, which is colder than if the region had been destitute of trees. It is within the experience of most cultivators of the soil that frosts sometimes strike hardest near a wood.
To the fact that under certain circumstances a forest may cause frost in the fields near by, we may add the qualification that this can only occur in the case of white frosts, and that whenever there is motion of the atmosphere, and the wind a cold one, the influence of the forest is always protective. An orchard sheltered by a wood may escape unhurt, while another in the same neighborhood not so protected may suffer the loss of its entire crop. This is believed to be not a very uncommon occurrence in the case of peaches.
If the fruit-growing interest of the country were to state its account with the forest, we should suppose it to be something like the following:
The Count against Forests.—1. Unfavorable to the free circulation of the atmosphere in summer-time; in this respect the influence of the forest is directly the opposite to that of an adjacent body of water. 2. Imparting moisture to the atmosphere, whereby, under certain conditions of the weather, the heat may become too great for the good of growing fruit. 3. Causing an occasional late frost in the spring. 4. Affording a harbor for birds and birds'-nests. This is no small consideration in some localities, where birds have to be slaughtered by the ten thousand to save certain kinds of fruit, as cherries, blackberries, and Delaware grapes. I speak advisedly, being well aware of the sentimentalism against which I offend. Some kinds of birds are, of course, only innocent and useful. I make no charge against them (nor against the forest which protects them). Let them live and sing! But, that birds which prey so remorselessly on fruits destroy insects enough to pay for the fruit they waste and consume, is very improbable, and we let the count stand against the trees and bushes that shelter them.
The Count in favor of Forests.—1. Usually equalizing the temperature between night and day during the summer-season—uniformity of temperature being a condition which is favorable to vegetable development. 2. Equalizing the effects of rainfall by storing up the waters to be given off gradually to the streams and the atmosphere, thus favoring the development of most kinds of fruit. 3. Imparting moisture to the atmosphere by transpiration through the leaves, and thus profiting the fields in various ways during a drought. This moisture may also contribute to the warmth of the atmosphere when warmth is beneficial. 4. Intercepting the sweep of the winds, and thereby lessening the mechanical injury to plants and trees, and weakening the cooperation for mischief of wind and cold. As a screen for protection against the wind, trees are not without appreciation, and it is generally understood that, even if they imparted no warmth to a cold wind passing through them, the mechanical resistance they afford prevents it from taking the warmth so readily out of vines, trees, and the soil. 5. Cooling the warm winds of winter and spring, thereby keeping back vegetation out of the way of late spring frosts. 6. Warming the cold winds in winter. The last three on the list being by far the most important; and by their cooperation they might very easily, and often do, make the difference, at a critical time, of a crop or no crop, as this often depends on a degree or two of temperature.
It will be readily perceived that all the better influences of wooded lands are of very much the same character as the influence of a body of water. It is when these two classes of conditions meet in the same locality that general fruit-growing has its best chances of success.
What proportion of woodland should remain in the interest of protection for agricultural and horticultural purposes, might be difficult to ascertain. Different localities would no doubt require a different proportion. Rentzsch (quoted by Marsh) estimates that for the interior of Germany about 23 per cent., and along the coast 20 per cent., is necessary for the needed protection. The case hardly admits of such precision; more would no doubt be better, and in a dry climate like ours, more than anywhere else.
So rapidly is the destruction of timber going on in this country that many localities originally covered with forest have not so great a proportion as this remaining, and other localities are in a fair way soon to be in the same condition. This is becoming, or at least should become, a real cause of apprehension to those who have the welfare of the farming interest, and especially of the fruit-growing interest, at heart. This continuous destruction of timber must eventually result in injury to the market value of lands in certain neighborhoods, especially lands for fruit-growing purposes.
The remnants of forests in the States have another enemy as inexorable and remorseless as the woodman's axe. Many forest-trees, like the wild Indian, do not seem to flourish in the midst of civilization. They first show signs of decay at the top. This takes place after the underbrush has been cleared away and the surface has lost that perfect mulch of decayed leaves which belongs to native forests. The trees are now liable to suffer from extremes of drought as never before. This change is equal to a change of habitat, and the consequence to some varieties of trees is loss of health and vitality.
According to the experiments of Prof. Pfaff made on an oak-tree, the amount of moisture lost by transpiration during the summer-season was more than eight times the quantity of rainfall on the same area for the same time. Dr. Hahn, who thinks this estimate quite too high, says, nevertheless, that "Herr Pfaff's results show us what an enormous quantity of water is required by isolated trees in a comparatively dry and free (bewegten) atmosphere, and how much they need the protection which they afford to each other in their combined capacity as a forest." Whenever the balance and integrity of the original forest is broken, the supply of water during droughts not being equal to the demand of trees now suffering the double disadvantage of needing more moisture and less of it available than before, death begins in the topmost branches, that part of the tree which is most exposed to the conditions of active transpiration and farthest removed from the source of moisture.
What should we do about this blight? Save the timber by using it before it is injured, and plant enough to make up for the loss.
For the application of the facts as now ascertained, let us take the southern shore of Lake Erie, which is a good fruit-region lying midway between the Eastern and Western cities, and affording to both part of their supply of fruit. Fruit does not do so well here now as it did in the early settlement of the country. Cut off the timber which still remains, and the injury to fruit-growing would be still greater; and so far as this result would have an effect, it would be to depreciate the market value of land. What this region especially needs is a protection of woodland against the cold westerly and southwesterly winds to cooperate with the benign influence of the lake in other regards. The more forest to the south of this belt of shore-land the better. The more frequently blocks and belts of woodland intervene throughout its entire extent for immediate local shelter and a general screen against westerly winds, the better for the farming and fruit growing interests of this region.
But, so long as it pays an immediate profit to cut down the forest, it will be done. It is not within the province of legislation to stop it. There is no hope from voluntary concert of action. A certain percentage of timbered lands might be exempted from taxation; but this innovation, though talked of, is slow in coming about. To a certain extent tree-destruction should be offset by tree-planting. The planter might not receive his profits so quickly as the destroyer, but nevertheless, wherever timber is likely soon to become scarce, and that is almost everywhere, profits would be sure to accrue from direct sales as well as from the value thus added to the land—generally and, besides the profits in dollars and cents, that accruing from the consciousness of having done a beneficent action.
There are a great many purposes for which timber, and timber only can be used; and for these purposes it should be religiously conserved. I once heard a gentleman say, "I don't worship my timber;" he sacrificed it to gain, in a perfectly legitimate manner it is true. Still the writer must say that he has a sincere respect for the "worship of timber;" it is not a bad kind of religion, so far as it goes.
Immense quantities of timber are slaughtered every year for fuel, and this, too, in a country where there is more coal than anywhere else in the world. There is but one way to stop this branch of the destroying process, and that is by increasing railroad facilities so as to make our coal-fields accessible to every part of the country. Cheap coal will save the timber. When no longer consumed in the millions of household fires in city and country, or in furnaces for the driving power of locomotives and mills, great will be the saving of timber for the necessary purposes for which timber must be used, and for the protection of our cultivated fields and gardens.
The burning of Chicago must make an immediate draft on timbered lands for certain purposes of building for which timber is still largely used. But this great fire, in proving the absolute necessity of building cities of brick, stone, and iron, will operate eventually to the saving of timber and the longer continuance of the protection which our northern forests afford against northern winds to the great agricultural districts which lie to the south of them.
And here I cannot but refer to a most short-sighted policy which our Government has been pursuing in giving a factitious value to lumber made from our own timber, by a so-called protective tax on foreign lumber. While this has operated directly against the building interests of our own people, it, at the same time, has led to the more rapid destruction of our own forests; and, in thus giving protection to the capital employed in lumbering, it is removing the protection which our forests afford to the American agriculturist, thus damaging the people at large in a twofold manner. This must be the case just so far as the forests belonging to the United States afford greater protection to our cultivated fields than is afforded by the forests of Canada. We do not realize the benign influence which our forests to the west and east of the great lakes exercise upon the climate and agriculture of the country. Imagine them all removed; the cold winds from the northwest and northeast, having unobstructed sweep, would reach us with greater force, and, passing over a bleak and treeless region, they would come to us absolutely colder. Our Government, by its protective policy, has been doing something to bring about this undesirable result. It is high time that a wiser policy should prevail, and that the Government should protect by taking its hands off. (It is gratifying to record that, since the above was written, the duty on lumber has been greatly reduced.)
There is no need of attributing more to forests than is their due. There are storms against which they afford no protection—avalanches of cold which rush down upon the country, killing fruit-buds, and even vines, shrubs, and trees. But these are exceptional. It is in the case of somewhat milder cold-storms that forests save, when without them there would be ruin. The great fact of the increasing uncertainty of fruit and agricultural crops with the continued clearing of the country, is a fact so patent, and of import so significant, that it alone is sufficient to prove the great value of forests for protection, and to put us on guard against their wanton destruction.
- Both De Vries and Sachs ascertained that every kind of plant has its special degree of temperature at which it makes most growth in a given time; but, while Köppen recognized this, his investigations have made an addition to our knowledge of the subject, his point being that the plant grows more when kept at a uniform temperature than if it had varied between extremes of which this temperature is the mean, thus showing that variation of temperature acts as a check on growth.
According to Karsten, great and sudden changes injure the health and hardiness of plants; while De Vries comes to a directly opposite conclusion. This, however, does not affect Köppen's result, which has reference to rapidity of growth. Moreover, even if great daily variation of temperature should not affect the health of plants, it might, nevertheless, be not wholly harmless to the tenderer fruits.
The preceding paragraphs have been suggested by the kinship between forests and lakes in their influence on climate and fruit-growing.
- Since writing the above, we have happened to fall upon several statements in favor of the influence of forests on rainfall, some of them from respectable scientific sources, Proctor, Bryant, Colver, etc. I learn, however, that Prof. Henry, of the Smithsonian Institution, has recently reported that observations for the last twenty years in this country show no appreciable influence of forests on the amount of rainfall. This should carry much more weight with it than the mere fashion of opinion about forests causing rain.
- Only Missouri, Nebraska, and Illinois, have legislative enactments to encourage the planting of timber. New York, Massachusetts, and California, do something in the same direction through their agricultural societies.
- According to an estimate in the Report of the Department of Agriculture for 1870, all the pine-timber in the region between the Mississippi on the west and Lakes Superior and Michigan on the north and east, will, at the present rate of consumption, disappear within the next twelve years, while the hard wood will last only about twelve years longer. Lumbermen do not take all, but what they leave is consumed by the fires which generally follow. About 330,000 acres are denuded annually in this region. This is only a part, perhaps, about half the annual consumption of timber in the northwestern section of our country. To compensate for this loss only about 150,000 acres are annually planted in timber throughout the entire West.
This destruction of timber is general. Even fruit-localities are not spared, as the writer has had abundant opportunity to witness, where the demand for railroad ties at high prices has created almost a furor for coining money out of the great oaks, regardless of consequences to climate and culture.
The alarm about the destruction of timber in this country is only too well founded.