THE IMPACT OF THE FOREST SITE TYPE ON THE INCREMENT AND CONE BEARING OF YOUNG GENERATIVE CEDAR FOREST LOCATED CLOSE TO SETTLEMENTS IN THE SOUTH OF TAIGA ZONE OF WESTERN SIBERIA

Abstract

Introduction. Cedar forests located near settlements in the south of the taiga zone of Western Siberia are cultivated forests. Here is the southern area border of the Siberian stone pine (Pinus sibirica Du Tour), so these forests occupy river terraces where the environmental conditions are not consistent with the environmental requirements of the species. Original (zonal) cedar forests are located in river valleys with highly humid soil. The territory unsuitable for cedar forest and selective felling distort the original gene pool of populations, lead to early age degradation and simplification of age composition. It is necessary to analyze increment and cone bearing potential of cedar forest located near settlements where there is a second generation of trees in order to predict the developmental prospects of the forest in general. The research is aimed at examining increment and cone bearing capacity of young second-generation cedar trees on the example of a typical for southern-taiga zone of Western Siberia cedar forest located on the area with heterogeneous environmental conditions. This is necessary to assess the prospects for further development of stone pine forests. Materials and methods. The study area is the north region between the Ob and the Tom river. The focus of the research are the two plots of young generative trees (average age is 84 years) located in neighboring areas with different hydrological soil regimes caused by a height difference of about 5 m. The first group (71 model trees) grows on grey forest soils of the 1st river terrace. The available moisture in the 20-centimeter root layer during the summer period is very low and amount to approximately 24 mm. The second group (62 trees) grows in a flood plain forest on humus-grey humid soils rich in nitrogen. The available moisture in the 20-centimeter root layer during the summer period is 170 mm. Both areas are characterized by the same density - 0.5. The size of trunk and crown, the length of the generative zone, the number of female and male shoots, the number of cones have been analyzed in the model forest. The structure of cones has been considered in detail, the quality of seeds has been assessed. Results. Young generative trees of the second generation growing on dryer soil terraces demonstrate lower increment and cone bearing capacity in comparison with the trees growing in the humid valley. The quality of the cones and seeds yield of trees growing on the terrace depends on the vegetative development of the crown: the larger the trunk and crown, the greater the yield of cones and seeds. In trees growing in the valley the features characterizing the development of cones and seeds are more closely interrelated. These differences indirectly indicate a lower resistance of trees growing on dry terrace soils. Conclusion. The valley bog proved to be more promising site for the formation of sustainable Siberian cedar forest, which in the south of the area represents the optimal forest growing conditions for Siberian cedar.