The study of the increment and the making of yield tables which had been inaugurated toward the end of the last century, by Oettelt, Paulsen, Hartig, and others, was just at the end of that century placed upon a new basis through Späth (1797), who constructed the first growth curves by plotting the cubic contents of trees of different ages, and through Seutter (1799) by introducing stem analysis, on which he based his yield tables.
On the shoulders of these, Hossfeld (1823) built, when he conceived the idea of using sample plots for continued observation of the progress of increment, and he also taught the method of interpolation with limited measurements, laying the basis for quite elaborate formulæ. But the first normal yield tables, based on the average trees of an index stand, were published by Huber (1824) and, in the same year, by Hundeshagen. From that time on, yield tables were constructed by many others, but only since the Experiment stations undertook to direct their construction is the hope justified of securing this most invaluable tool of forest management in reliable and sufficiently detailed form. Even the newest tables are, however, still deficient, especially in the direction of detailed information regarding the division into assortments. The yield tables of Baur, Kuntze, Weise, Lorey, and others are now superseded by those of Schwappach for pine and spruce, and of Schuberg for fir.
As a result of the many yield tables which gradually accumulated, the laws of growth in general became more and more cleared up and finally permitted their formulation as undertaken by R. Weber (Forsteinrichtung, 1891).
The idea of using the percentic relations for stating the increment, and of estimating the future growth upon the basis of past performance for single trees was known even to Hartig (1795) and Cotta (1804) who published increment per cent. tables. The methods of making the measurements of increment on standing trees were especially elaborated by Koenig, Karl, Edward and Gustav Heyer, Schneider (his formula, 1853), Jaeger, Borggreve, and especially by Pressler (1860) who opened new points of view and increased the means of studying increment by causing the construction of the well-known increment borer, and in other ways.
The most modern text-book which treats fully of all modern methods of forest mensuration giving also their history is that of Udo Müller (Lehrbuch der Holzmesskunde, 1899), superseding such other good ones, as those of Baur (1860-1882), Kuntze (1873), Schwappach (short handbook, last edition 1903).
The many sales of forest property which took place at the beginning of this period naturally stimulated the elaboration of methods of forest valuation. Even the soil rent theory finds its basis at the very beginning (1799) in a published letter by two otherwise unknown foresters (Bein and Eyber), who proposed to determine the value of a forest by discounting the value of the net yield with a limited compound interest calculation to the 120th year. This idea was elaborated, in 1805, by Nœrdlinger and Hossfeld into the modern conception of expectancy values, and the now familiar discount calculations were inaugurated by them. Cotta and Hartig participated also in the elaboration of methods of forest valuation; Cotta writing his manual in 1804, recognizes the propriety of compound interest calculations, while Hartig, 1812, still uses only simple interest, and exhibits in his book as well as in his instructions for practice in the Prussian state forests rather mixed notions on the subject.
Altogether, even in the earlier part of the period, there arose considerable difference of opinion and warm discussions, in which all the prominent foresters took part, as to the use of interest rates and methods of calculation. But this warfare broke into a red hot flame when Faustmann (1849) with much mathematical apparatus developed his formula for the soil expectancy value, and when Pressler and G. Heyer transferred the discussion into statical fields, making the question of the financial rotation the issue. Then the advocates of the soil rent and of the forest rent theories ranged themselves in opposite camps. This war of opinions, although abated in fervor, still continues, and the issue is by no means settled.
The discussion of what should be considered the proper felling age or rotation naturally occupied the minds of foresters from early times; a maximum volume production being originally the main aim. As early as 1799, Seutter had recognized the fact that the culmination of volume production had been obtained when the average accretion had culminated. Hartig, in 1808, made the distinction of a physical, an economic and a mercantilistic, i.e., financial felling age, and Pfeil, considerably ahead of his time, is the first to call (1820) for a rotation based on maximum soil rent. As, however, he had so often done, he changed his mind, and while he first advocated even for the state a management for the highest interest on the soil capital involved, he later rejected such money management. About the same time Hundeshagen clearly pointed out the propriety and proper method of basing the rotation on profit calculations, but it was reserved for a man not a forester to stir up the modern strife for the proper financial basis, namely Pressler, a professor of mathematics at Tharandt, who became a sharp critic of existing forest management, and developed to the extreme the net yield theories.
It was then that the danger of a shortening of the existing rotations, due to the apparent truth that long rotations were unprofitable, called for a division into the two camps alluded to; G. Heyer, Judeich and Lehr, elaborated especially the mathematical methods of the soil rent theory, Krafft and Wagener came to the assistance of Pressler, while Burkhardt, Bose, Baur, Borggreve, Dankelmann, Fischbach and others, pleaded for a different policy for the state at least, namely, the forest rent with the established rotations.