Dinamics of the Radial Growth of Siberian Pine Pinus sibirica Du Tour under Different Thinning Modes

Abstract

Creation and formation of Siberian pine forests for various purposes, and especially Siberian pine seed orchards, is an urgent issue of Russian forestry. The article deals with the dynamics of the radial growth of Siberian pine Pinus sibirica Du Tour trees after thinning with different modes (method, number of methods, etc.). The analysis was performed both at the stand, and tree levels. The studies were carried out at the experimental plots located in the Khanty-Mansiysk autonomous district and Tyumen region in the middle taiga subzone. As a result of the research it has been established that the response of Siberian pine to thinning depends on intensity, number of methods and timing, as well as on age and morphological structure of Siberian pine on clearings and under the canopy of secondary forests. It was found that extensive (low density) Siberian pine seed orchards are formed both under intensive and systematic thinning. In this case, the average radial growth ranges from 3 to 5 mm/yr, which provides not only a rhythmic progressive growth, but also physiological development. Thereby, after 30-35 years substantially all trees have already entered the generative phase and actively seeding. Single thinning, especially with small selection (less than 50 %) leads to the formation of intensive (high density) seed orchards with an average growth of trunk from 2 to 3 mm/yr. Overgdense, aside from reduction of Siberian pine radial growth, slows down the rate of ontogenetic stages and phases. As a result, in these seed orchards there are trees that have never given cones.