Читать книгу A Brief History of Forestry - B. E. Fernow - Страница 24

Organized forest management was slower to develop than silvicultural methods. The first attempts to bring order into the progress of fellings took the form of dividing the whole area into a certain number of felling areas (12, 16, 20, 30, etc.), several ordinances dating from the middle of the 15th and 17th centuries containing prescriptions to that effect.

It is doubtful whether the numbers of these areas indicate years of rotation, in which case they could only have applied to coppice, or whether they indicate periods of return in selection forest, although the historians seem to jump to the former conclusion. The area division practiced by v. Langen in the Harz mountains (1745), who prescribed the division of larger districts into fifty to sixty, of smaller districts into twenty to thirty felling areas, also leaves it doubtful, whether the areas corresponded to an assumed rotation or to a period of return.

At first, the division was not into equal areas, for no survey existed, and its object was simply to localize the cutting and provide orderly progress. The subdivision was made in the mountain country by following the topography, valleys and ridges, while in the plain the lines opened up for purposes of the chase (to set up nets), called Schneisen or Gestelle (rides), bounding square areas called Jagen, Quadrat, Stallung, were used for the limitation of the felling areas. Most commonly, however, largely due to absence of surveys, the ordered division did not materialize, but existed only on paper.

With more exact measuring of areas, and with the conception of a rotation or longer periods of return, it was recognized that the inequality of the sites or soil qualities, especially in mountain districts, produced very unequal felling budgets. To overcome this inequality, Jacobi, in Goettingen (1741) introduced proportional felling areas, making the felling areas on poor sites permanently larger.

Similarly, v. Langen and Zanthier attempt to secure equal annual returns without slavishly holding to the geometric division, merely making sure that the total area be cut over in the predetermined rotation.

The first attempts to introduce a regulated management by making a volume division the basis is recorded from the Harz mountains in 1547. This method, based on very crude estimates although upon very fair forest description, was continued into the 18th century.

In the last half of the 18th century all these crude methods were improved, and applied on extensive areas.

In 1785, Zanthier combined area and volume division, determining the felling budget on each felling area by counting and estimating the trees and calculating how many trees could be used annually under a sustained yield management; the area division being used only as a check or means of control.

A very considerable advance was made by Oettelt, (who surveyed and regulated the Weimar forests in 1760) in the elaboration of details and establishment of proper principles for regulating the felling budget.

In his forest description he introduces for the first time periodic age classes, usually six, but of uneven length: Young growth, below twelve years; thicket, twelve to twenty-four years; polewood, twenty-four to forty years; clear timber, forty to fifty; medium timber, fifty to seventy-five; mature timber, seventy-five years and over.

He divides the forest into proportional areas (which were marked by stones in the woods), equalizing them according to age, quality, increment, soil, exposure, so as to secure equal annual budgets; the stands were ranged into seven or eight unequal age classes and each into as many annual felling areas as there are years in the age class; if some of the age classes were absent, he extended the time for cutting in the older class until the younger had grown to the proper age and by varying the cut from good to poor sites for stands he tried to even out the budgets. The volume budget he determined by average increment measurements. This method was, however, much too far advanced and required too much mathematics to find imitators at that time.

Another method which proved also too complex for the foresters of the time was that of v. Wedell; nevertheless, by 1790, he had by it put into working order 800,000 acres in Silesia. He divided this area into districts, the districts into blocks or management classes, and used an elaborated proportional area division for determining the felling budget. He distinguished quality of stand and quality of site, and made four site classes. The volume of stock, he found by means of sample areas, to which he added the increment in order to find the total volume for harvest, when it could be determined how long with a given budget the stands would last, or what average annual felling budget could be taken before the next age-class would be mature.

In the North German plain, with very uniform conditions of soil and timber, the method of equal felling areas was the most natural and most easily applied.

Frederick the Great, who took a considerable interest in forestry matters, ordered such an area division for the State pineries in 1740, fixing upon different numbers of felling areas, but finally, in 1770, deciding on a rotation of seventy years. Lack of personnel retarded progress in this forest survey and regulation until in 1778 v. Kropff undertook the direction. Not agreeing with his master regarding the short rotation of seventy years, he arranged to have each district divided into two working blocks, and by cutting alternately in these, managed to double that rotation. His successor, Hennert, in 1788, devised a new method by introducing allotment of a number of annual felling areas to a period of the rotation when at least the periodic budget could be equalized. A value or money yield equalization of the felling budgets was also attempted.

For easier handling, the forest was divided into small compartments or Jagen and a classification of four, still uneven, periodic age classes (of different length for conifers and broadleaved forest), and three site qualities were employed. The merchantable stock was ascertained by a sample area method and the felling budget by dividing the oldest age class by the number of years it must last until the next was ready. Since no attempt was made to secure a proper age class gradation, the method failed to improve conditions for the next rotation.

Some 500,000 acres were regulated according to this plan in Prussia, probably very superficially.

In 1789, Bavaria also ordered a division into annual felling areas.

In all these methods of regulating the yield or budget, the area played the main role, the volume being only a secondary consideration.

The first elaboration of a pure volume division was made by Beckman in 1759. He estimated stock on hand by trees and guessed more or less at the increment, allowing 2.5, 2, and 1% for the different sites, and then made a year to year calculation of stock for 125 years. How the felling budget was finally determined is not known.

Two methods were simultaneously devised in Württemberg in 1783, which form the transition to the so-called allotment methods, making periodic age classes of an equal number of years and allotting either felling areas or volumes to each period of the rotation. Incapacity of the officials prevented the application of the one method, while the other, devised by Maurer, remained also only a proposition.

But, in 1788, Kregting in his Mathematical Contributions to Forestry Science teaches a pure volume allotment method with ten year age classes and nearly all the apparatus which was afterward developed by Hartig, who in the next period dominated to such a large extent the development of forestry in all its branches.