Читать книгу A Brief History of Forestry. - Fernow Bernhard Eduard - Страница 31

Natural regeneration continued to be the favorite method well into this period, and, for a long time, selection forest and coppice were all that was known in practice until Hartig and Cotta forced recognition of the shelterwood system.

The only way in which a transition from the generally practiced, unregulated selection forest to an intensive management was possible, with the ignorant personnel of underforesters, was to formulate into an easily intelligible prescription the necessary rules, allowing the least play to individual judgment. This was done by Hartig when he formulated his eight “General Rules” (1808) which coincided also closely with the teachings of Cotta. Since these rules represent in brief and most definitely the status of silvicultural knowledge on natural regeneration at the time, it may be desirable to translate them verbatim.

(1) “Every forest tree which is expected to propagate itself by natural regeneration must be old enough to bear good seed.

(2) “Every district or stand which is to be replaced by a thoroughly perfect stand by means of natural regeneration, must be brought into such position (density) that the soil may everywhere receive sufficient seeding.

(3) “Each compartment must be kept in such condition (density) that it cannot, before the seeding takes place, grow up to grass and weeds.

(4) “With species whose seed loses its power of germination through frost, as is the case with the oak and beech, the compartments must be given such a position (density) that the foliage which after the fall of seed covers and protects the same cannot be carried away by wind.

(5) “All stands must be given such density that the germinating plants in the same, as long as they are still tender, find sufficient protection from their mother trees against heat of the sun and against cold.

(6) “So soon as the young stand resulting from natural regeneration does not any longer require this motherly protection, it must gradually, through the careful removal of the mother trees, be accustomed to the weather, and finally must be entirely brought into the open position.

(7) “All the young growths, whether secured by natural or artificial seeding, must be freed from the accompanying less useful species and from weeds, if these in spite of all precaution threaten the better kinds.

(8) “From every young forest until it is full grown, the suppressed wood must be removed from time to time, so that the trees which are ahead or dominate may grow the better; the upper perfect crown cover, however, must not be interrupted until it is the intention to grow a new forest again in the place of the old one.”

Since these rules are applicable only in beech forests, much mischief and misconception resulted from their generalization; pure, even-aged high forests became the ideal, and the mixed forest, which was originally the most widespread condition, vanished to a large extent. This was especially unfortunate in Northern and Northeastern pine forests.

A reaction against Hartig’s generalization began about 1830, under the lead of Pfeil. He had at first agreed with Hartig, and then with equal narrowness advocated for many years a clear cutting system with artificial reforestation. Finally, however, he was not afraid to acknowledge that his early generalizations in this respect were a mistake, and that different conditions required different treatment.

In the development of the shelterwood system there was at first, under the lead of Hartig, a tendency to open up rather sharply, taking out about three-fourths of the existing stand, but gradually he became convinced that this was too much, and finally reduced the first removal to only about one-third of the stand. This was the origin of his nickname of Dunkelman. In spite of the fact that it was claimed that Cotta took the opposite view (for which he was called Lichtman), he, too, grew to favor a dark position, and, as he progressed, leaned more and more towards more careful opening up. Hartig originally recognized only three different fellings: the cutting for seed; the cutting for light; and the removal cutting. By and by, a second cut was made during the seed year, and the number of fellings to secure gradual removal were increased, so that, by 1801, this system seems to have been pretty nearly perfected to its modern conditions. The best exposition of this Femelschlagbetrieb (shelterwood system), as then developed, is to be found in Karl Heyer’s Handbook, 1854.

The method was unfortunately extended by Burgsdorf (1787) to the Northern pineries with a seventy year period of rotation. Within ten years, however, he recognized its inappropriateness, and modified it by instructions to leave only six to twelve seed trees per acre. His successor, Kropff, reduced the number of seed trees to four or five, which were to be removed within two or three years. In spite of the development of this more rational method, the practitioners under Hartig’s approval, held mainly to a dark position even for pine, much in the manner of a selection forest, which produced a poor growth of oppressed seedlings, retarding for a long time the development of the pineries.

In spruce or fir, either a pure selection forest or a strip system was employed. Attempts at a shelterwood system were made, but experience with the wind danger soon taught the lesson that this was not a proper method with shallow-rooted species. Even Hartig preferred for spruce clearing and planting, and this is still the most favored method with that species. For the deep-rooted and shade-enduring fir the shelterwood method with a long regeneration period was thoroughly established in the Black Forest, and in Württemberg by 1818.

Natural regeneration being the main method of reproduction until the beginning of the 19th century, artificial means, as is evident from the forest ordinances of Prussia and Bavaria (1812 and 1814), were usually applied only to repair fail-places, or to plant up wastes. In this artificial reforestation, with the exception of the planting of oak in pastures, sowing was almost entirely resorted to because it could be done cheaper and easier, but as the sowings were mostly made on unprepared soil and with very large amounts of seed (30 to 60 pounds per acre, now only 7 to 10 pounds), the results were not satisfactory, either because the seed did not find favorable conditions for germinating, or when germinated the stand was too dense.

Planting, if done at all, was done only with wildlings dug from the woods, and usually, following the practice of the planting of oak in pastures, with saplings: the plant material was too large for success. Nurseries, except for oak, were not known, even to Cotta in 1817; and Heyer, having to plant up several thousand acres, still relied on wildlings, two to three years old, which he took up with a ball of earth by means of his “hole spade,” a circular spade re-invented by him and much praised by others. Hartig, in 1833, still advised the use of four to five year old pine wildlings, root-pruned, but, eventually, having met with poor success, for which he was much discredited, came to the conclusion that un-pruned two-year-old plants were preferable.

The credit of having radically changed these practices belongs to Pfeil, who, entirely reversing his position, advocated for pine forest a system of clearing followed by sowing, or by planting of wildlings with a ball of earth. Then, suggesting that possibly planting without this precaution could be attempted, and pointing out the necessity of securing a satisfactory root system, he recommended, about 1830, the use of one-year-old seedlings grown in carefully prepared seed beds. While for securing these, he relied upon the simple preparation of the soil by spading, Biermans added the use of a fertilizer in the shape of the ashes of burned sod. The method of growing pine seedlings and planting them when one to three years old was further developed by Butlar (1845), who introduced the practice of dense sowing in the seed beds. He also invented an ingenious planting iron or dibble, a half cone of iron, which was thrown by the planter with great precision, first to make a hole and then to close it. This was improved by the addition of a long handle into the superior, well-known and much used Wartenberg planting dibble. At the same time (1840), Manteuffel devised the method known by his name of planting in mounds, which is especially applicable on wet soils.

It was not until 1840 that transplanting of yearling pines with naked roots became general. The widespread application of this latter system resulted in abandoning to a large extent mixed growth, and led to the establishment of pure pine forests, introducing thereby most intensively all the dangers incident to a clearing system and pure forest which are avoided by the mixed forest, namely, insects, frost and drought.

A practice of planting spruce in bunches, originally twelve to twenty plants in a bunch, had been in existence since 1780. This practice increased until 1850, and is still in use in the Harz mountains and in eastern Prussia, although the bunches have been reduced so as to contain only from three to five plants, the object of the bunching being to make sure that one or the other of the plants should live. Much discussion as to the merits of this method took place between the old masters, Cotta favoring the small bunches upon the basis of a successful plantation of his own, Hartig and Pfeil opposing it, but finally weakening. Since 1850, however, the practice of setting out single plants has become more general.

A reaction from the indiscriminate application of the shelterwood method to the hardwoods and of the clearing method to the pine set in during the last quarter of the 19th century under the lead of Burkhardt and Gayer. These advocated return to mixed forest and to natural regeneration with long periods, approaching a selection forest. Gayer especially, professor of silviculture at Munich, became the foremost apostle of this school. Yet even to this day, the principles of silvicultural treatment under the many different conditions remain unsettled. On the whole however, with the financial question assiduously brought forward, the clearing system has made most progress, and the selection system has nearly vanished, being replaced by the group method and the shelterwood system.

A number of special forms of silvicultural management applicable under special conditions have been locally developed, without, however, gaining much ground and being mainly of historical value. Among these may be mentioned Seebach’s Modified Beech Forest, which consists in opening up a beech stand so as to secure regeneration, merely to form a soil cover, leaving enough of the old stand on the ground to close up in thirty or forty years. By this treatment the large increment due to open position is secured without endangering the soil. Similarly the Storied or Two-aged High forest, was applied to the management of oak forest in mixture with beech. In a few localities also, on limited areas, a combination of forest and farming (Waldfeldbau) has been continued and elaborated, besides the more general use of coppice and coppice with standards.

According to the statistics for 1900 the following distribution of the acreage under different silvicultural methods prevailed throughout the empire:

Coniferous forest, of which 68 % is pine and 30 % spruce, prevails in Eastern and Middle Germany, deciduous forest, of which 20 % is oak, the balance principally beech, in the West and South.

Coppice and coppice with standards are mostly in private hands as well as the coniferous selection forest, the State forests being almost entirely high forest, i.e., seed forest, other than under selection method.

Methods of Improving the Crop. The credit of having first systematically formulated the practice of thinnings under the name of Durchforstung (for the first thinning), Durchplenterung (for the later thinnings), belongs to Hartig, although the practice of such thinnings had been known and applied here and there before his time. He confined himself mainly to the removal of the undesirable species, dead and dying, suppressed and damaged trees, being especially emphatic in his advice not to interrupt the crown cover. Excepting the early weeding or improvement cuttings, these thinnings were not to begin until the fiftieth to seventieth year in the broadleaved forest, but in conifers in the twentieth to thirtieth year.

The first attempt to explain on a biological basis the process and effect of thinning was made by Späth in a special contribution (1802). Cotta, in his Silviculture, although at first agreeing with Hartig, later in his third edition (1821) changes his mind, and improves both upon the biological explanation of Späth and the practice of Hartig, pointing out that the latter came too late with his assistance, that the struggle between the individuals should be anticipated, and the thinning repeated as soon as the branches begin to die; but he also recognizes the practical difficulty of the application of this cultural measure on account of the expense. Curiously enough, he recommends severer thinnings for fuel-wood production than for timber forests.

Pfeil accentuates the necessity of treating different sites and species differently in the practice of thinnings. Hundeshagen accentuates the financial result and the fact that the culmination of the average yield is secured earlier by frequent thinnings. Heyer formulates the “golden rule:” “Early, often, moderate,” but insists that first thinning should not be made until the cost of the operation can be covered by the sale of the material. Propositions to base the philosophy and the results of thinning on experimental grounds rather than on mere opinion were made as early as 1825 to 1828, and again from 1839 to 1846, at various meetings of forestry associations, until, in 1860, Brunswick and Saxony inaugurated the first more extensive experiments in thinnings. The two representatives of forest finance, Koenig and Pressler, pointed out, in 1842 to 1859, the great significance of thinnings in a finance management as one of the most important silvicultural operations for securing the highest yield.

In spite of the advanced development of the theory of thinning, the practice has largely lagged behind, because of the impracticability of introducing intensive management. Only lately, owing to improvement in prices and the possibility of marketing the inferior material profitably enough to justify the expenditure, has it become possible to secure more generally the advantages of the cultural effect. Within the last thirty or forty years, great activity has been developed among the experiment stations in securing a true basis for the practice of thinning.

New ideas were introduced through French influence and by others independently in the latter part of the eighties, when the distinction between the final harvest crop (Fr. élite, le haut) and the nurse crop (le bas) was introduced.4

The physiological reasons for the practice of thinning upon experimental basis, were advanced by the botanists Goeppert and R. Hartig, and among foresters, the names of Kraft, Lorey, Haug, Borggreve, Wagener, and others are intimately connected with the very active discussion of the subject lately going on in the magazines. Thinnings have become such an important part of the income of forest administrations (25 to 40 % of the total yield) that the prominence given to the subject is well justified, and a more modern conception of the advantages of thinnings and especially of severer thinnings is gaining ground.

The proposition, now much ventilated, of severe opening up near the end of the rotation, in order to secure an accelerated increment (Lichtungshiebe) is, however, much older; Hossfeld, in 1824, and Jäger in 1850, advocated this measure for financial reasons, while Koenig and Pressler anticipated the development of an individual tree management by pruning, and differentiation of final harvest and nurse crop, a method which is working itself out at the present time.