The impact of growing regimes for planted Scots pine stands on the quality characteristics of the tree trunk phytomass components in the left-bank part of the Northern Steppe of Ukraine

Abstract

Introduction

The examination of the thinning effect on the wood quality in planted Scots pine (Pinus sylvestris L.) stands in different forest site types is important. Such studies make it possible to evaluate the bioproductivity of stands and assess the extent of the use of the ecological potential of local growing conditions, based on the annual production of pine stands.

Materials and Methods

The impact of high-intensity selective and linear-selective thinning treatments on natural and basic densities of wood, wood in bark, and bark of trunks in planted pine stands has been investigated. The study focused on middle-aged (51–52 years) pine stands in permanent experimental plots in the left-bank part of the Northern Steppe in Ukraine. Several thinning treatments of varying intensities have been carried out within the selected stands. The study was carried out in contrast variants in terms of stand density (1,500–700 trees?ha^-1 and 2,700–1,600 trees?ha^-1) in fresh relatively poor (B₂) and dry poor (A₁) forest sites. Forest mensuration and typological studies were carried out according to generally accepted methods (Hrom 2010, Vorobyov 1967). Tree trunk natural and basic densities for above-ground phytomass components were analyzed using the method of Lakida & Yudytsky (1993).

Results

The changes in the basic density of wood in different parts of the trunk and in different experimental variants were similar. The basic density decreased as the height of the trunk increased. In forest site type B₂, basic wood density in all parts of the trunk in thinned stands was 8–25% higher than in denser stands. In forest site type A₁, in contrast to B₂, the changes in the wood basic density in dense and thinned stands were similar along the trunk height and did not differ statistically.

Conclusions

In the left-bank part of the Northern Steppe in Ukraine, in dry poor sites and in fresh relatively poor sites, no significant influence of the thinning intensity on the quality of pine wood was found in young and middle-aged planted pine stands. Important factors that affect the density of wood are the soil moisture and fertility.

A significant difference in the basic density was observed between the variants with different soil fertility and moisture, in particular between the fresh relatively poor forest site and dry poor forest site. For the dense stands, the average basic wood density in dry poor forest sites was 18% higher compared to fresh relatively poor forest sites. For thinned stands, these differences were 8%. For the average basic bark density, the values were 30% and 46% for dense and thinned stands, respectively, and for the average basic density of wood in bark – 18% and 19%, respectively.

In the steppe arid climatic conditions in Ukraine, in dry poor sites, and in fresh relatively poor sites, it is advisable to carry out high-intensity thinning of planted pine stands at a young age by linear or linear-selective methods. In a middle-aged pine stand, the first high-intensity thinning (up to 30% of the growing stock) should be carried out in a selective method. Such growing regimes for pine stands help increase their average heights and diameters, improve resistance to physical stress, and do not negatively affect the wood quality i.e. do not reduce its density.

The wood in the lower third of the trunk of pine trees is of better quality because its basic density is higher than in the upper part of the trunk. This fact should be taken into account when determining the quality of harvested wood.

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