STRUCTURE AND GROWTH OF PRELIMINARY GENERATION OF SPRUCE OF DIFFERENT DENSITY AFTER BIRCH FELLING IN THE SOUTHERN TAIGA OF EUROPEAN RUSSIA

Abstract

Introduction. Influence of the density of plantings on the formation and growth of forest stands remains the matter of attention for many researchers. Most of these studies are about forest plantations or pure natural even-age forest stands. Influence of the density of preliminary generation of spruce on the structure and productivity of small-leaved forests grown after felling is still faintly studied. The goal of the research is to study the effect of density of the remaining part of preliminary generation of spruce after birch felling on the structure and growth of forming spruce forests. Objects and methods of research. The research was conducted in the southern taiga subzone (Rybinsk district, Yaroslavl region) in the facilities of the Institute of Forest Science, RAS.  Observations of preliminary generation of spruce after birch felling were made on two  permanent sample plots (total area 0.7 ha), where the dynamics of horizontal (parcel) structure of plantations and morphometric characteristics of trees were observed for 24 years in the monitored mode. The analysis of the effect of population density on the structure and growth of spruce was performed for the most common group of parcels, where the dominant parcel is the polewood of spruce. The total density of spruce  in the studied sites varied from 2.8 to 11.3 thousand pcs. ha ^-1. Results and discussion. The structure and growth of spruce after birch felling in connection with the density of preliminary generation of spruce within the group of parcels formed by polewood of spruce are considered in accordance with 20-year observations. After felling, formation and growth of preliminary generation depends on the state, number, and morphometry of spruce trees in the year of felling.  Increase in density of population of spruce causes slowing of the processes of differentiation of trees and not always leads to the increase in forest stands productivity. The best structure of stand is in the areas with the total density of spruce of 4-6 thousand pcs. ha ^{– 1}.Dependence between the number of trees of the first and second layers in 20 years after felling with the total number of spruce trees immediately after birch felling is established. Trees of the lower layer (undergrowth) react better to felling - in the first 10 years after felling, average increment in height increases by 7.4 – 8.0%, in terms of trunk volume - by 13.6-14.0%. The trees of upper layer grow with less intensity, it particularly concerns the parcels with high density of spruce. In the second decade, the percentage of growth decreases in all the layers. Increase in the volume of trunk has significantly slowed down. During this period, the intraspecific competition is increasing, and the impact of the changed environmental conditions on the growth of trees is less evident. For parcels with the polewood of spruce, high total number of spruce trees immediately after felling does not always lead to the increase in productivity of spruce stands, which is explained with lower morphometric indicators of trees in dense spruce forests. Сonclusion. In the parcels with spruce in the stage of polewood, the structure and growth of preliminary generation of spruce depends on its size and condition of trees in the year of felling. In the first decade, the trees of lower layer (undergrowth) react better to the birch felling regardless the density of spruce. The reaction of trees of upper layer is less evident, it particularly concerns populations with higher density (11,0 thousand pcs. ha^-1).  In 20 years after birch felling, the plots of parcels with the total density of spruce population of 4-5 thousand pcs. ha^-1 show better figures. Productivity of forest stand is 2  bonitet classes better,  stock of stem wood increases by 9-11 times. Decrease or increase in the initial density of spruce population from this optimum leads to the decrease in the stock of spruce stem wood under the considered conditions.