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Chapter VII. Methods Of Forest Crop Production
Economics of forestry; a reference book for students of political economy and professional and lay students of forestry, by Bernhard E. Fernow
CHAPTER VII. METHODS OF FOREST CROP PRODUCTION: SILVICULTURE.
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There is nothing that needs to be more strongly emphasized and impressed upon the American public, and even upon the young professional forester, than that the main business of the forester is expressed in the one word "reproduction"; his main obligation is the replacement of the crop he has harvested, whether produced by unaided nature or otherwise, by as good, if not a better crop of timber than he found.
Silviculture, the technique of the growing of wood-crops, a branch of the broader subject of arboriculture, is the pivot upon which the whole forestry business turns.
As the farmer sows and reaps, so the forester harvests and replaces, although the methods of the two have little in common. Nor are the methods employed in other arboriculture pursuits applicable, such as the orchardist uses where the fruit is the object, or the landscape gardener, who looks for æsthetic effect, or the roadside planter, who desires the shade.
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The tree which satisfies these arboriculturists does not at all satisfy the requirements of the forester, for his point of view, his aim, is a different one and hence his methods are his own. In fact, single trees are not his object any more than the single grass blade is the object of the farmer; the largest amount of wood in the most salable or profitable form is his aim, logs rather than trees, and the financial results from their harvest. The final aim of the silviculturist is, therefore, attained only when he has removed the old trees and replaced them by a young crop. He grows trees in masses and for their substance. Not only does he deal with trees in masses, but with trees in natural conditions, being by financial considerations often limited in the use of artificial aids and methods, such as the other arboriculturists and the farmer in his crop production may employ.
Restricted as he is, or finally will be, to the poorer soils and conditions, those least favorable to agricultural production, he is forced to the most conservative management of the natural conditions in order to secure a desirable result without too much expenditure, which his long-maturing crop cannot repay.
The simplest method of harvesting the crop of nature and replacing it is to cut clean or clear the ground and plant or sow the new crop, the farmer's method. This is called "artificial reproduction" or "reforestation," and is largely practised in Europe.
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It is, of course, the only method applicable where the forest crop is to be started anew on abandoned fields, on the forestless prairies and plains, on the burnt areas which have grown up to useless brush, in short, where no old crop of desirable species is on the ground. Where an old crop of desirable kinds is already on the ground, the same method of clearing followed by artificial reforestation may be employed, but there is also a choice of producing the new crop by seeds falling from the trees of the old crop, by "natural regeneration."
This method is the one by which nature maintains the forest. As trees grow old, decay, and fall, an opening is made into which the neighboring trees throw their seeds and fill up the gap with a new seedling growth. The forester profits from this observation, and with the recognition of the laws under which forest growth develops, as detailed in the preceding chapter, he gives merely direction to this development in such a manner as to reduce the unfavorable and increase the favorable conditions of development for whatever kinds he may desire to propagate, avoiding the use of the planting tool, and managing to secure the reproduction and development of the young crop by the mere use of the axe in the old crop. But he uses the axe differently from the lumberman.
The lumberman, the first exploiter of the mixed virgin forest, treats it like a mine from which he
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takes the pay ore, culling the best kinds and cuts, and abandoning the rest to its fate, which is usually made hazardous by fires running through the forest, fed by the debris he has left.
If these fires have not killed the remaining growth, he may come back after a few years, and may find some of the smaller trees of the useful kinds, which he had left standing, grown to such a size as will pay to cut and transport to market; these he calls "second growth." Possibly he may repeat this culling process several times; but finally the desirable kinds are cut out, and there is left a growth of undesirable kinds, of weeds which he has helped in their struggle with their rivals of useful kinds, by the removal of the latter.
Meanwhile, wherever an opening is made by the cutting of trees, seeds from the neighboring growth fall to the ground and sprout, giving rise to some aftergrowth, but this is apt to be preponderantly of the undesirable kinds which were left; moreover, this young growth under the shade of the old trees, being deprived of the desirable amount of light, develops slowly and poorly. As a result of these operations, then, not only the present composition of the growth is deteriorated, but also its future. Thus, in Kentucky, where the valuable white oak used to form 40 per cent of the forest, the aftergrowth contains hardly 5 per cent; and in Michigan, Wisconsin, and Minnesota, where the white pine has been culled our severely, its absence
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in the young growth has led to the curious belief among lumbermen that it does not propagate itself by seed.
The forester, on the other hand, treats the forest as a permanent investment and as a crop. All his operations keep in mind continuity and permanency for the future. Reproduction not only, but reproduction of the most useful kinds1 and superior quality is his aim.
[Note 1: 1 Of the nearly 500 species native to our country, only about 70 furnish wood of sufficient size and quality to deserve the attention of the forester.]
The forester, instead of culling out the best kinds first, as the lumberman does, would take out the undesirable ones first, and thus improve the composition of his crop. The material which results from these so-called "improvement cuttings" may sometimes not directly pay for the labor spent on them, but they are cultural operations, designed to put the property in more useful condition for the future, and hence they are at least indirectly profitable.
When in this way the desirable kinds have been given the advantage (or sometimes simultaneously with the improvement cuttings), a gradual removal of these takes place, either of single individuals here and there, or of groups of them, making larger or smaller openings; or else more or less broad strips are cleared, on which the seed falling from the remaining neighboring growth can find lodgement,
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and sprout; and, as the young seedlings require more light for their development, gradually more of the older timber is removed, or the openings are enlarged for new crops of young growth, and thus the reproduction is secured gradually, while harvesting the old crop.
Finally, when the last stick of old timber has been removed--and in a well-developed forestry system every stick is expected to be utilized--a young growth composed as far as possible only of the more useful kinds has taken the place of the virgin forest, to grow until it becomes profitable to harvest again, when the same methods will secure another reproduction, and so on.
To be sure, these operations are not quite so simple as they appear from this statement, for considerable knowledge of the requirements of each species and judgment of the needs of the young crop for its best development are needed to secure a successful regeneration, two requisites secured by study and experience, which, for American species and conditions, are still lacking to a large extent.
The progress and manner in which the natural regeneration by seed is secured give rise to variously named methods and to various results in the appearance and development of the young crop; but in all of these so-called natural regeneration methods the young crop is secured by seed falling from the mother trees on or near the ground to be recuperated,
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and the old crop is removed more or less gradually, to make room for the young crop, the main difference being in the rapidity with which the old crop is removed.
The choice of method depends upon financial as well as silvicultural considerations.
In protection forests and luxury forests, in which the financial questions become secondary and the requirement of a continuous soil cover may be paramount, the choice of method is circumscribed by this consideration. Here, methods in which the old crop is very slowly removed and replaced by the new crop are indicated, even if financial and silvicultural results would make other methods desirable.
In supply forests, the cheapest method which secures desirable proportionate results in the crop is to be chosen. This must vary according to local conditions. Climate, soil, and species to be dealt with call for silvicultural considerations; the relative cost of planting and of logging or harvesting under different methods influence the financial results.
The clearing process followed by artificial replacement entails a money outlay for the latter from year to year; the gradual removal methods with natural seeding avoid, to be sure, this outlay, but, since to secure the same amount of harvest, a larger territory must be cut over, they entail large initial investment for means of transportation, which
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must be maintained for all the years of removal, and they occasion also otherwise greater expenses in the harvest than the concentrated logging in the clearing system, which may be done over temporary roads. Where, as in Germany, most forest districts are provided with well-built permanent road systems, gradual removal methods are often probably the least expensive; but in the United States, in most places, unless water transportation can be relied upon, a gradual removal system means heavy initial outlays for roads, which may make the clearing followed by planting the cheaper method. It is in most conditions also the surer; for a complete success of the young crop can, in most cases, be forced. In the natural regeneration methods there are elements of uncertainty, the seed years may not come when expected; in a mixed forest, which, for many reasons, is the most desirable form, the species seed irregularly, have different requirements of light, so that the composition cannot be very well controlled; the damage and loss occasioned in the young crop by the removal of the old crop must be discounted in the final result; and besides, where the removal is very slow, the young crop is impeded in its development by the shade of the old crop. These systems, therefore, are better adapted to shade-enduring species than to light-needing. The main argument and the most important in favor of these methods is that they furnish protection to the soil, preventing its
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deterioration under the influence of sun and wind, to which the soil is liable in a clearing system, and giving also protection to the tender seedlings of such species as are subject to frost or drought. Under such conditions, therefore, i.e. where protection of soil and young crop are necessary, the gradual removal methods will be chosen.
Over 80 per cent of the forests of Germany are managed under a clearing system and rapid removal systems, and only 20 per cent under slow removal and other systems.
Where, as in our culled forests, the valuable species have been removed and the weed trees have been left in possession, it stands to reason that no natural regeneration method will reëstablish the better species; they must be restored by artificial means. Finally, where conditions permit, a combination of natural and artificial methods may be resorted to in order to secure the best result.
The crudest, least intensive method is an improvement on the method of the lumberman, who culls the best trees here and there, the so-called method of selection. The improvement over the lumberman's practice, who is concerned only in the removal of the useful timber, consists in looking somewhat after the fate of the young growth, protecting it against competing species, giving it light as soon as practicable by further culling, and improving the composition by reducing
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the weed trees and also leaving more seed trees.
The result is a forest in which all ages and sizes are scattered over the entire area, coming nearest to the conditions of nature.
This system, in which the young crop has a poor chance to develop, and which is applicable to shade-enduring species only, is recommended for protective forest areas. In Germany it is applied only on small areas and on the steepest slopes, less than 10 per cent of the German forest area being managed under it, and in the Prussian state forests, less than 1/2 per cent.
The continuous soil cover, to be sure, is a feature which is its greatest recommendation, but this is secured at great expense and loss in accretion.
To permit a better chance for the young growth, the so-called "group method" has been lately devised, in which not single trees, but groups of trees, are removed and the opening is expected to be seeded by the neighboring trees. From time to time, as soon as the young growth is well established, the opening is enlarged and additions of young growth secured in the form of an irregular ring or band around that of preceding years.
An older method, similar to the last, consists in making the opening in the form of a narrow strip at right angles to the prevailing winds, and as the ground is seeded to clear a new strip toward the
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windward side. This "strip method," just as any method which relies upon the seed furnished by a neighboring growth, is more successful with those kinds which have light-winged seeds, easily carried by the winds over the area to be seeded, and which do not require any protection in their infantile stage. It is a method which, on account of the greater concentration in harvest, is probably advisable in many cases in the United States.
For heavy-seeded kinds like oaks, beech, hickories, and other nut trees, the more complicated method of "regeneration under shelter wood or nurse trees" becomes necessary; this consists in a series of severe preparatory thinnings of the old crop which is to be reproduced, beginning a year or more before the time when a full seed crop is to be expected, seed years recurring more or less periodically. These preparatory thinnings are made for the purpose of exposing the soil to atmospheric influences, which hasten the decomposition of the litter, thereby securing a serviceable seed bed. Enough trees of the kind to be reproduced are left on the ground to secure full seeding and shelter and protection of the young crop. When the latter has come up, the nurse trees are gradually removed to give the young seedlings the required light. The whole operation, until the last nurse trees are removed and the young crop is established, may take from three to ten and more years, according to kinds, soil conditions, climate, and success
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in securing the seeding. The greatest nicety of judgment is required to direct these operations, taking into account the requirements of the species and the conditions and progress of development of the young crop.
To secure a full crop by this natural method often requires, not only careful manipulation, but patient waiting for years, since trees do not bear seed every year and the young crop may from this or other causes fail to establish itself wholly or in part, when another seed year must be awaited, or the "fail" places filled out artificially by planting.
The artificial reforestation may be made either by sowing the seed or by transplanting seedlings secured from nurseries or from the woods. This planting or sowing is done after more or less careful preparation of the soil, the preparation and manner of planting depending on soil conditions, species, and financial considerations.
Simple and effective as these artificial methods are, there are certain dangers connected with them, which follow their injudicious application. The exposure of the soil may lead to its deterioration, the sun-warmed areas are apt to breed insects, the standing timber, exposed to sweeping winds, may be thrown when the opening is large.
Where in a natural seeding a hundred thousand seedlings would cover the soil and quickly replace the shelter removed in the old growth, economy will permit the planting of only a few thousand
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(usually 2500-5000 per acre), and it requires years before the crowns of the young growth close up to shade the ground thoroughly, meanwhile weeds and grass sapping its strength and retarding the development of the crop. Nevertheless, by a judicious application, making the openings small, utilizing the shelter of some left-over trees for partial protection, increasing the number of plants, or sowing a cheap nurse crop, these dangers may be avoided.
Theoretically, however, the regeneration under shelter wood with a short period of removal is considered the most efficient.
While all these methods rely upon a reproduction of the new crop by seed, directly or indirectly, there is another mode of reproduction possible, owing to the capacity of some trees to reproduce new parts from buds, forming shoots from the stumps after the old tree is cut. These stool shoots, or sprouts, grow into trees, and by the mere harvest of the old crop, the new crop is secured. This, in turn, may be cut, and the stump will produce again and again new sprouts. This simplest and crudest system of reproduction, called "coppice," which results involuntarily when the old hardwoods are cut, is applicable only to the broad-leaved trees which are capable of producing valuable shoots in this manner; the coniferous trees, like pines, spruces, etc., are practically excluded, although some possess the capacity of sprouting in inferior degree.
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Even in broad-leaved trees the capacity for sprouting is possessed in different degree by the different species, and is more or less lost by all in old age; and especially after repeated harvests the stumps become exhausted and die, so that the forest is apt gradually to deteriorate in composition as well as in density, unless fresh blood is added by reproduction from seed.
Thus in Pennsylvania, where the system has been in vogue for a century and more to furnish charcoal for the iron furnaces, the valuable white oaks and hickories have been crowded out by the chestnut, which is a superior sprouter; similarly, in Massachusetts the inferior white birch replaces the more valuable kinds in the coppice, as their stocks weaken and fall a prey to rot.
Another disadvantage of this coppice system under which the woodlands of deciduous trees in almost all New England and the Atlantic States are reproduced is that, although the sprouts develop much faster than the seedlings from the start, they soon fall off in their growth, and are capable merely of furnishing small dimensions and fire wood. The coppice, therefore, is useful only for certain purposes, but cannot be relied upon to furnish material for the great lumber market.
The deterioration consequent to the continued application of the coppice is best studied in Italy and in certain parts of France, where serviceable
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timber is almost unknown, and fagots of small fire wood are precious articles.
To avoid this objection a mixed system has been practised, by which part of the crop (the so-called standards) is allowed to grow up and be reproduced by seed, while the other part is treated as coppice; but in this so-called standard-coppice (Ger. Mittelwald, Fr. taillis composé) the standards, unimpeded in their branch development, do not form serviceable trunks, and in addition, by their shade injure the coppice growth.
While, then, these methods are of limited use, the only method of reproducing the forest which is to serve as a basis for the supply of the enormous quantities of saw timber required in the markets is the so-called timber forest, the high forest, Hochwald of the Germans, or futaie of the French, which is reproduced by seed, and grows to full size and maturity, to be again so reproduced.
As in the natural methods the axe is the only tool which is used to secure the regeneration, so is the axe the only tool which cultivates the young crop, such cultivation consisting in the judicious removal of surplus trees by the so-called thinnings, by which the quantity and quality of the crop is increased. To understand this, it is necessary to know that trees form wood by the function of the foliage under the influence of light.
Hence a tree with much foliage and unimpeded access of light is bound to make much wood.
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These conditions are fulfilled when the tree is allowed to grow in open stand, as on a lawn, without close neighbors, who would cut off some of the light supply.
But trees under such conditions grow mostly into branches, the crown being developed at the expense of the bole, which remains short and more or less conical in shape, of little commercial or technical use, except for firewood; when the trunk is sawn into boards every branch appears as a defect, known as a knot, which makes it unfit for use in the better class of work, and thus, while the total quantity of wood in the tree is increased by the open stand, it is done at the expense of quality.
The object of the forester, however, is not simply to grow wood, but to produce wood of such form and quality as is useful in the arts. The ideal tree for him is one with a long, cylindrical, branchless trunk, bearing its crown high up, which when cut into lumber produces the largest amount of material clear of knots, of straight fibre, and giving the least amount of waste or fire wood.
His aim, therefore, must be to so place his trees that, while the largest possible amount of wood shall be produced, it shall be deposited in the most useful form also.
By a close position, when each tree cuts off the side light from the neighbor, the formation of branches is prevented, or the branches which were
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formed, being overshadowed, soon lose their vitality, die, and finally break off, leaving the shaft smooth, and, if this clearing was effected before the branches had reached considerable size, the amount of clear lumber is increased.
But again, if the trees are kept too close, if too many trees are allowed to grow on the acre, each one having the smallest amount of foliage and light at its disposal, the amount of wood produced by the acre may be fully as large as it is capable of producing, but it is distributed over so many individuals that each develops at the very slowest rate, and hence does not grow to useful size in the shortest time.
To secure his object, producing the largest amount per acre of the most useful wood in the shortest time, the forester must know what number of trees to permit to grow, so as to balance the advantages and disadvantages of close and open position.
This number differs not only according to the species composing his crop, but also according to soil and climatic conditions and to the age of the crop, as we have seen in the preceding chapter.
Some trees, having considerable capacity of enduring shade, like the beech, sugar maple, or spruce, may require many more individuals to the acre than the more light-needing oaks or pines; on richer soils fewer individuals will produce
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satisfactory results, when on poorer soils more individuals must be kept on the acre. The question of the proper number of trees to be allowed to grow per acre at different ages is one of the most difficult, on which practitioners differ widely. In general, however, the practitioner has recognized the necessity of preserving a dense position for the first twenty to thirty years of the young crop, sacrificing quantitative development to quality and form. The close stand secures the long, branchless, cylindrical trunk, which furnishes the clear saw-logs of greatest value. Then, when the maximum rate of height growth has been attained, a more or less severe thinning is indicated, in order to secure quantitative development, and these thinnings are repeated periodically, to give more light as the crowns close up, and also to utilize such of the trees as are falling behind in this wood production.
As a result of judicious thinnings, the rate at which the remaining crop develops may be doubled and quadrupled, the heavy, more valuable sizes are made in shorter time, and, where the inferior material removed in the thinnings is salable, a much larger total product is in the end secured from the acre, for many of the trees which were removed and utilized would have died, fallen, and decayed in the natural struggle for existence.
In German forest management the amount utilized in thinnings amounts to 25 per cent and more of the final harvest yield.
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Other considerations also influence these operations, such as the preservation of soil moisture, which is the most essential contribution of the soil to tree growth, and which requires the soil to be kept shaded.
In fact, there is nothing that a forester guards so jealously, next to the light conditions at the crown, as the soil conditions: a soil cover free of weeds and grass, and covered as amply as possible with a heavy mulch of decaying leaves and twigs, and if this best protection of the soil moisture be deficient, a cover of shrubby undergrowth which requires less water than weeds and grass--this is the character of a desirable forest floor.
Altogether it will have appeared that the entire silvicultural requirements of the crop resolve themselves into one, namely, proper management of light conditions, which is secured by the judicious use of the axe.
While in field crops it is customary to grow only single species, in pure stands, the forester has discovered that, as a rule, not only better results, both in quantity and quality, but better protection of soil conditions and especially safety against many dangers from insects, frosts, and storms, etc., can be secured by mixed plantations, and hence he gives preference to mixed crops, although such crops, composed of several species, require more skill in their management.
While the crop is developing, it is, of course,
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necessary to protect it against damage of various kinds. The young seedlings of some species are apt to suffer from frost or drouth, which is avoided by growing them under shelter of older trees, by draining wet places, securing opportunity for cold air to draw off, etc.,--mostly preventive measures. In prairie and plain it may be possible to assist their resistance to such damage by cultivating the ground as the farmer does, but in the real forest country such means are excluded by the character of the ground, and the expense. Altogether the only practical remedies lie in the direction of foreseeing the damage and guarding against it.
Animals, and especially insects, are frequently injurious to the young crop, and insects also to old trees, by their defoliation. This damage, too, can be largely obviated by preventive measures.
Since many, if not most, injurious insects are monophagous, i.e. feed on one species, or at least one genus, mixed forests resist their damage better, since the number of host plants is reduced and the intermixed trees impede progress and development of the pest. Fewer insects develop in the dense shade and on vigorous, healthy plants, hence they can be kept in check to some extent by keeping the crop dense and in vigorous development, when it can resist the attacks; and also by keeping the woods clean of débris, dead and dying trees, in which insects develop; finally, as ultima ratio,
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positive measures must be resorted to for collecting and destroying the broods of insects before they have time to do damage. Considerable amounts of money are spent in this direction in European forest management, amounting in ordinary times to from one-half to one cent per acre, but, from time to time, the pests break out in such numbers that no remedies will avail.1 Some loss must be sustained, which is, however, of less moment if the crop had already developed to suitable size and can be harvested when the trees have been killed.
[Note 1: 1 In Bavaria, in one year (1891), $500,000, or 20 cents per acre of property and $1.80 per acre infested, were spent in combating one insect, the nun, without much effect. The premature harvesting of 60,000,000 cubic feet was the result of the damage.]
Wind-storms are a danger to older timber, especially of shallow-rooted species, like the spruce, and on soft soils and exposed slopes or mountain tops. Here care must be taken in keeping the stand well thinned, so that the trees may get accustomed to the swaying of the winds in more open stand. In this way they are induced individually to form a better root system and become wind-firm, while in the dense stand their strength was only in the union with neighbors.
Under conditions where damage from windfall is to be expected, it becomes necessary to arrange the felling areas so that no stand of old timber be suddenly exposed to the prevailing winds by the
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removal or harvest of a neighboring stand. Since the prevailing winds in the northern zone come mostly from the western direction, it is sought to secure an arrangement of the stands of different age in series (a "felling series"), so that the old and tall timber is found at the eastern end, the age classes grading off to the west, the youngest at the western end, and the tops of the series of stands ideally appearing like a roof slanting down from east to west. It is apparent that, under such an arrangement, the old timber can be harvested and reproduced without exposing any stands to the force of the wind, and the young timber is growing up under the influence of winds and becomes windfirm.
The greatest danger to forest properties, however, is fire, and the protection against this most unnecessary evil, resulting mainly from man's carelessness, absorbs a large part of the energy of the forester. Proper police, but also silvicultural measures, reduce the amount of danger and damage.
The damage which fire occasions is very variable, according to a variety of conditions. Most forest fires are confined to the forest floor, running in the litter and young wood, scorching the older trees merely; yet, under favorable conditions, the fire may run up to the trees, becoming a crown fire and propagating itself from top to top and throwing firebrands and sparks to the ground, often for long distances.
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Young crops, during the seedling and brushwood stage, are readily killed, while older timber may stand scorching without much or any damage. Different species behave differently in this respect. The giant trees, or Sequoias, covered with a dense bark more than a foot thick, and their wood hardly inflammable, the Douglas fir, with a similar protection, are less liable to be damaged than the thin-skinned firs or spruces, beech or white birch and aspen. The green, succulent foliage and wood of broad-leaved trees is more resistant than the dry resinous foliage and wood of conifers. Drouthy conditions and dry soils are more likely to induce danger from fire damage than the opposite conditions. Finally, the presence or absence of an undergrowth, or dédris, of dead and dry branches of trees, and the character of the forest floor, must make a difference in the ease with which a fire may start and run, the amount of heat it develops, and the consequent damage.
The damage may consist in the total loss of the crop, which is usual until the pole-wood stage is reached. In pole wood and young or old timber the trunks may be only blackened, but more often the cambium layer below the bark is partially or entirely killed, causing either the death of the tree, especially when recurring fires accumulate the damage, or secondary damage results through rot or insects which develop, especially in the weakest trees.
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A damage even greater than the loss of the crop is experienced in the loss of the soil cover, the litter and duff, which is the forester's manure. This loss may become irreparable in localities where only a thin layer of mineral soil overlies the rock, and the opportunity for starting a new crop may be entirely destroyed. The fire danger in the United States is so great that in many localities it almost prohibits the practice of forestry; for who would want to invest money and energy in a property which is exposed to extra risks from fire by the absence of proper legislation, or by the lack of police and moral support on the part of the community in enforcing it, by the unpunished negligence or malice of incendiaries, and by the populational conditions of the country, which prevent the economical disposal of the débris from logging operations.
The last-mentioned difficulty is perhaps the most important, because practically almost impossible to avoid. There must, especially in our virgin woods, always result from the harvest of the useful material a large amount of débris, tops, branches, brush, and other waste, which cannot be marketed; and this not only impedes the development of a young crop, but adds to the danger from fire until decay has reduced the débris, which often requires many years, even decades.
The proposition has been made to burn the débris after the logger. This is not as simple and
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inexpensive as it appears, when care is to be taken not to damage the remaining growth and especially when natural regeneration is to be practised, or a young crop, already in part provided by nature, is to be saved.
Where the culling is made light, only here and there a tree being taken, especially in the mixed forest, the amount of débris also is small and it may be left to natural decay, with the only precaution that the branches of the top are lopped so as to have the whole mass come into as close contact with the ground as possible, when the decay proceeds more rapidly.
But where the culling is severe, as is often called for in pure woods and also in mixed stands, and a large amount of débris results, even this lopping of tops is of no avail; the fire risk continues for many years. Incessant watching during the dangerous season is necessary, and even this proves futile, for a fire, easily started by the slightest carelessness or by lightning,1 will run in the débris so fast that no human power can stop it.
[Note 1: 1 Although undoubtedly most fires are the result either of malice, foolishness, or carelessness, namely, by smokers, campers, farmers in clearing brushlands, and others using fires, locomotives throwing sparks from smoke-stacks and ash-pits, the writer can attest that lightning is occasionally the cause of fires. The old "snags," dead trees, the result of previous fires, are especially liable to be struck by lightning, and being dry, they burn, and propagate the fire either by the flames burning down to the ground, or else by sparks and burning limbs falling to the ground; but the writer has also seen live trees, even of hardwoods, blaze when struck by lightning, and propagate the fire in spite of a pelting rain. Of 509 fires occurring in the Bavarian state forests during 6 years, 4 were demonstrably accredited to lightning and 7 to locomotives. Of 156 conflagrations in the Prussian state forests during 10 years, 3 were the result of lightning and only 4 from locomotives, 7 years out of the 10 being without any record of fire from this last cause, and that on a property of 7,000,000 acres, over half of which was stocked with pine on dry sandy soil.]
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Partial burning and piling of the brush reduce the danger somewhat, but hardly in proportion to the expense. The readiest remedy, where forestry is to be practised under such conditions, is to make a clean sweep, that is, clearing, burning up the débris, and replanting, or else, if natural regeneration is to be relied upon, adopting the strip system, when the opportunity of burning the débris totally is still possible.
The danger from the débris continues longer in coniferous woods than in the deciduous-leaved, the wood of which decays more readily in contact with the ground, although usually, in these latter, larger amounts of débris result. For instance, in the hardwood forests of the Adirondacks, the merchantable log material presents only one-third of the total amount of wood, two-thirds being cordwood and débris. The only hope here, in the absence of a paying home market for fuel from this inferior material, is to establish chemical works for its conversion on a large scale into charcoal, acetic acid, wood alcohol, and other useful manufactures.
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In fact, the application of silviculture, i.e. the systematic production of wood-crops as a business proposition, in our culled, mismanaged woodlands throughout the United States is, in most cases, possible only where the means exist of utilizing this inferior material; for the risks from fire are too great, or else the cash which would otherwise have to be spent in making room for the young crop will surely exceed reasonable proportions. Only the state or other long-lived corporations can afford to spend money now in the hope of adequate returns in a distant future.
That it is finally possible to reduce the fire danger to a minimum by proper police regulations and by silvicultural measures, and by proper management and organization, is attested by the forest fire statistics of the German forest administrations, to which we have already referred on pp. 137 and 190.
To these we may add that in any given longer period within the last 25 years the acreage destroyed in Prussia or Bavaria (about 10,000,000 acres) rarely exceeds .005 per cent of the total forest area under state control. In a recent report (1896) we read of "very considerable damage by fire" occurring in the Prussian state forests, referring to the burning over, not total loss, of 2500 acres. One fire is reported as destroying 1000 acres of a "hopeful" pine and spruce plantation 20 to 25 years old. In the next year (1897) the entire loss
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was not over 100 acres. This comparative immunity is due to both administrative and police regulations.
The Indian forest administration, under circumstances not much less difficult, nay, perhaps more difficult, than those prevailing in the United States, refutes the assertion that forest fires may not be suppressed.
Not only have the people of all timbered parts of India practised the firing of woods for many centuries, for purposes both of agriculture and pasture, but the natural conditions in many of the Indian forests are such as to discourage the most sanguine.
The forest in most parts is a mixed growth, of which a considerable portion is valueless and is left to die and litter the ground with dry and decaying timber, furnishing ready fuel. A dense undergrowth, largely composed of giant grasses and bamboo, covers the ground, green or dry, to which is added a mass of creeping and climbing vegetation. It is a dangerous forest, with hot, dry winds to fan the flames; and yet the forest department fights and prevents fires, and succeeds in a measure. The efficiency of protection has constantly increased with perfection of methods, and the expenses have never exceeded $10 per square mile in any year on an area of over 30,000 square miles, of which, in 1895, not more than 8 per cent experienced damage. The police regulations
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which lead to such results will be discussed in a succeeding chapter.
Here the preventive silvicultural measures and arrangements in the forest, which are designed to reduce the fire danger, are to be only briefly enumerated.
The experience that deciduous-leaved woods are less liable to danger suggests the maintenance of mixed forest; the fact that old timber is comparatively safer, and that on large wind-swept areas the heat and the rapidity of progress of a fire is increased, leads to distributing the felling areas, and that means the areas of young crop, isolating them, making them smaller, and having them surrounded by older timber. Removal of the dead and dying trees by systematic thinnings wherever possible, and the disposal of the slash from logging operations, are obvious means of reducing the danger.
In German forest districts, more especially those unduly exposed to fire danger, a subdivision of the forest into blocks surrounded by avenues, or so-called rides, of 8 to 40 rods width, is made. These rides, kept free from inflammable material by annual burning, or perhaps by sowing to grass, serve the purpose of confining the fire within the block, and furnishing a base from which to fight a fire, for which the frequent roads may also be utilized.
But these openings are worse than useless unless kept in proper condition, and unless the forces to
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fight the fire are on hand, for if débris is allowed to accumulate on them, this dries out more readily, and, in addition, the draft of air along the rides only increases the fury of the fire. In older deciduous-leaved woods the shade keeps the ground moist, the fire runs more slowly, and a wider opening would in most cases prove undesirable.
The same may be said regarding rights of way for railroads. The wide swath usually made, and usually not kept clear, but rather accumulating inflammable débris, exposes the soil to the drying effects of sun and wind, and besides, creates drafts of air, fanning the sparks into flame. There would be more safety in a narrower opening, which the shade of a dense stand of timber, especially if of deciduous-leaved trees, would keep moist, with a tendency to extinguishing the sparks. The objection that the falling of trees would impede and endanger the traffic might be overcome by gradually removing those liable to fall.
Through specially endangered districts, i.e. in coniferous forest, safety strips running along the right of way may be maintained. On these, on both sides of the track, a strip of ground 25 feet wide is entirely cleared of all inflammable material, which may, if practicable, be used for farm purposes; this is skirted by a strip of woods 50 to 60 feet wide, which remains wooded, acting as a screen for the sparks from locomotives, but is also kept clear from inflammable materials by annual raking
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and burning. Where this is not sufficient, a ditch 5 to 6 feet wide and a foot or so deep is opened on the outside of this strip toward the endangered woods, the soil being thrown toward the track side and possibly planted with a light-foliaged, deciduous-leaved species; cross ditches through the safety strip every 300 feet add further to the safety by confining any fire within reasonable limits. The whole arrangement requires not over 200 feet, and that mostly usefully occupied, while furnishing almost absolute security.
Such a system would be applicable in many cases in our own country. It would, with some slight changes, be perfectly feasible, and in the end profitable, for railroad companies to grow their tie timber in this way, using such light-foliaged rapid growers as black locust, catalpa, etc.
Forest crop production as a business, silviculture, will become practicable and profitable in this country only when reasonable forest protection is assured by proper exercise of state functions.
Until this is secured, lumbermen will continue to exploit the natural forest without much regard to its fate after they have secured its present valuable stores, for they cannot afford to assume the hazard of the fire danger.
Before positive silvicultural methods are applied by them, they may find it advantageous to cut the virgin forest more conservatively, they may find that it pays in the long run better not to cull too
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closely, that it is advantageous to leave more of smaller sizes, i.e. to limit the diameter to which they remove trees, so that they may return sooner for a second cut, and also to avoid unnecessary damage to the young volunteer crop. At present the limitation of size to be cut or to be left uncut is based upon calculations of immediate profits to be derived, and does not take into account any future considerations, since the lumberman does not cut with a regard to the future, but attempts to secure the largest present gain. He views the forest as a mere speculation. To curtail his present revenue for the sake of a future revenue by abstaining from cutting all that is marketable is the first step toward changing this point of view, introducing the idea of continuity, and treating the forest as permanent investment.
It must be understood, however, that the limitation on the size of trees to be cut or to be left uncut has not necessarily any bearing on the replacement of the crop; it is not silviculture. It is in the main a financial measure, it being demonstrable that it pays better to leave small-sized trees to accumulate more wood before utilizing them, or else a device to prevent overcutting of a valuable species, so that it may not be eradicated too soon, a wise measure wherever systematic attention to positive silviculture cannot be given.
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