Farber S. K., Kuzmik N. S. Determination of Forest Soil Fertility by Forest Planning Data

Values of forest inventory indicators are the result of cause-effect relationships of stands with environmental factors. Forest soils, along with the amount of heat and moisture, are the main components of forest vegetation conditions. The fertility of forest soils therefore can be evaluated (measured) by means of forest inventory parameters. The regression equations are formed. As a function, the site productivity class (bonitet) of the stand is used, as an independent variable, the indicator that quantifies forest vegetation conditions. The data of mass forest inventory – the description of forest inventory compartments--contain all the information necessary for the formation of equations. The description of the section also contains soil characteristics, including the soil name (type). We can write down: B_s = f(S), where: B_s is the bonitet class of the stand, depending on soil fertility; S is an indicator of forest vegetation conditions. As an indicator of forest conditions, the d/d₀ ratio was previously proposed, where: d₀ = f(h); d, h – diameter and height of the main tree species of the stand (Farber, 1997). In general, the advantage is of an indicator that varies less than the others. Therefore, as a measure of forest vegetation conditions in the work, the ratio of heights S = h/h₀ is used. In this case, the averaged growth line in height (regression equation, h₀ = f(A), where A is the stand age, years) is used as a reference point. By introducing an additional argument, the accuracy of determining h₀ increases. The diameter is used as an argument of this kind, then h₀ = f(d, A). The two-factor equation defines the origin in the form of a plane. The ratio of heights S = h/h₀ is determined for each forest inventory compartment of coniferous tree stands. Next, the average S_i values for the tree species and soil names, and the total weighted average S₀ for coniferous tree species and soil names are calculated. Thus, each soil type receives a quantitative measure. With the name of the soil in the description of the forest inventory compartment, regardless of the stand species composition and land category (stand, burn, logged area), we obtain a quantitative assessment of forest soils fertility with the ability to determine the potential tree species productivity. The paper demonstrates a map where, for the test site, the fertility of forest soils is shown by means of the values of S₀, and the potential productivity of coniferous trees is shown by means of yield classes.