Наукові праці Лісівничої академії наук України (Dec 2021)
Influence of Betula pendula Roth. on mensurational indices of Pinus sylvestris L. in forest plantations of fresh soil conditions of Western Polissia
Abstract
In order to increase the productivity and sustainability of forests in specific conditions, measures to improve soil conditions of forests and effective use of potential soil fertility are becoming of particular importance. Increasing soil fertility can be achieved through appropriate selection of tree species in cultivated plantations and the establishment of them close to optimal composition. Therefore, it is important to devise rational schemes and methods of tree species mixing during the creation of forest plantations with the participation of Pinus sylvestris L. and Betula pendula Roth. in poor soil conditions, where Scots pine would be characterized by high productivity and stability using soil-improving effect of silver birch. The feasibility of introducing silver birch into Scots pine plantations is the subject of long debate in the scientific literature; however, the conclusions of researchers are ambiguous. The investigation of silver birch impact on Scots pine in poor soil conditions is the biological basis for developing forestry measures to regulate the share of deciduous species in birch-pine plantations in order to improve the growth of Scots pine and ensure its superiority in the plantation. The aim of the study was to determine the effect of individual rows of Betula pendula on the average height and diameter of Pinus sylvestris in a 6-row strip of trees and to determine the optimal number of rows in a pine strip at a certain width between rows. Scots pine in fresh soil conditions cannot accumulate high stocks of stem wood due to the poor soil conditions of forested plot, therefore it grows in correspondence to site index 3 according to M.M. Orlov’s scale. Exceptions are poor soil conditions that are closer in terms of forest vegetation effect to relatively poor conditions or in terms of close to optimal participation of silver birch in the composition, where pine can grow according to site index 2. Strong suppression of silver birch by Scots pine in forest plantations of moist soil conditions, especially in the case of the introduction of mixing rows, cannot be an unequivocal reason for the inexpediency of introducing birch as a companion species in pine plantations. It is found that in the conditions of fresh soil types of pine forest, the influence of silver birch on the growth of Scots pine is positive. The main roles are played by the accepted scheme of mixing, the width of the rows and the number of rows of pine in the strip, which determines the range of positive effect of silver birch on coniferous species. The impact of silver birch on Scots pine largely depends on the width of the rows. The narrower the row spacing, the more rows of pine come under positive effect of birch due to the acceleration of precipitation decomposition, but, at the same time, the negative impact of deciduous species on the adjacent row of pine increases. Under soil conditions A2 with a 2-meter width between rows, the positive effect of birch extends to four rows of pine, namely with the introduction of the mixing scheme 1r.Bp 4r.Ps (hereafter Nr – number of rows; Bp – Betula pendula Roth.; Ps – Pinus sylvestris L.). Herewith the width of the strip of trees reaches 10 m. Taking into account the range to which the positive influence of birch extends, for 1.5-meter width between rows the recommended mixing scheme will be 1r.Bp 6r.Ps. Under soil conditions A2 using the scheme of mixing 1r.Bp 4r.Ps and plant spacing 2.0 × 0.5 m and initial density of 10.0 thousand pieces / ha, the initial participation of birch would be 20%; according to the scheme of mixing 1r.Bp 6r.Ps and plant spacing 1.5 × 0.5 m and the initial density of 13.4 thousand pieces / ha, the participation of birch in the initial composition would be equal to 15%.The specified share of deciduous species using indicated technological elements to create forest plantation is close to optimal.
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