ENVIRONMENTAL TYPES OF WOOD STAND GROWTH YIELD
The rationale for research is in the necessity to refine evaluation techniques of forest yield and inventory standards, showing the regularities of their growth rates. The work is aimed at modelling of pine wood stands growth in terms of their mean height, mean diameter and mean inventory, supported with environmental feasibility study of growth curves features depending on the forest site type. Materials and methods. The research is focused on the natural pine wood stand growing in different kinds of forest sites of the Kostroma Region covering 1,013 thousand ha which amounts to 23.3 % of the forested area. We used a multiple regression equation combining synergetic combinations of binary variables, encoding forest types with the age of wood stands and the growth function of Korsun-Backmann as a growth model. Results. The paper provides environmentally-based explanation that a growth curve form in wood stands, which starts from one point at the beginning, then feature differences and then in a number of cases come to the same point again, which points to the asynchronous character of dynamic changes. The most intensive young stand growth rate at a young age is observed in the best soil and environmental conditions on relatively rich mesophilic and mesohydrophilic soils. This stand becomes mature earlier than a stand growing in worse conditions on poor or overhydrated soils. However, when a stand growing in better conditions, starts to decline, a stand growing in worse conditions is still growing; it takes longer to become mature. It implies that the most probable age changes in the indicators should be linked to the forest site types rather than to quality classes, which are only relatively graded, but are functionally not linked to the environmental factors. Development of a general classification scheme of the soil and environmental conditions in different forest regions is bound to enable detection and generalization of the regularities of wood stand growth course by climatic gradients based on above stated methodical solutions. The authors come to a conclusion that the growth models of wood stands represent not only inventory standards, but also a programme for managing stand development, therefore, these models should be constructed not by their quality classes but should be based on the forest site types.