State, marketability and assortment structure of planted oak stands in the Left-Bank Forest-Steppe after thinning operations of different intensity

Abstract

Introduction

Thinning is a forestry measure aimed at growing economically valuable stands. It is implemented through periodic felling of those trees whose further preservation as a part of stands is impractical. Peculiarities of thinning in oak forests depend on the species composition, the age of the stands, and the growing conditions.

Despite the available studies of the features of thinning in the oak forests of the country, including the Left-Bank Forest-Steppe, the question of the intensity and duration of their maintenance is still controversial.

The aim of the research was to determine how thinning (in older stands, usually over 40 years) of different intensities influences mensuration characteristics, health condition, and marketability and assortment structure of planted oak stands.

Materials and Methods

The research was conducted at a stationary multivariate research object established in 1934 in the Neskuchanske Forestry in the Trostianetske State Forest Enterprise. Thinning was carried out with low (15% of the total stock), moderate (22%) and high (29%) intensities.

Surveys in the sections of the research object were carried out at the ages of the stands 42, 46, 53, 55, 60, 70, 75, 83, 97, and 126 years (in 2018). Thus, the total observation period was more than 80 years.

The oak stands were investigated during the last survey according to the methods generally accepted in forestry and forest mensuration. The research on the sections was carried out taking into account the corporate standard “Forest Inventory Sample Plots”. The conditions of trees and stands were assessed in accordance with the Sanitary Forests Regulations in Ukraine.

Results

The results of the 80-year-old research showed that in all sections of the experiment, high-quality mixed stands with two layers were formed. The total relative density of stocking of the stands in the sections, depending on the intensity of thinning, ranged from 0.94 in the section with a heavy intensity of thinning to 0.98 in the section with a low intensity of thinning.

The largest diameter of 51.4 cm at the age of 126 years was recorded for the oaks in the section with a moderate intensity of thinning. In the section with a heavy intensity of thinning, the diameter was less by 2%, and in the section with a low intensity, it was less by 4%. The oak in the section with a heavy intensity of thinning had the highest height at the age of 30.7 m. In the section with a moderate intensity of thinning, the oak height was lower by only 1%, and in the section with a low intensity – by 5%.

The largest proportion of commercial oak trunks was recorded in the section with a moderate intensity of thinning (100%), and the smallest (78%) one was found in the section with a heavy intensity. The highest yield of merchantable wood was observed in the section with a moderate intensity of thinning (336 m³·ha^-1). In the sections with low and heavy thinning intensities, the yield of merchantable wood was lower by 4 and 7% (320 and 311 m³·ha^-1, respectively).

The yield of assortments that can be obtained from trunks of larger diameters, namely, barrel log and fineline veneer, will be the largest in the section with a moderate intensity of thinning (77 and 153 m³·ha^-1, respectively), and the smallest one will be in the section with a low intensity (61 and 127 m³·ha^{- 1}, respectively).

The health condition of the stands in all sections was assessed as “weakened”, with a low damage.

Conclusions

The stands in the section with a moderate intensity of thinning (22% by stock) had the largest values of diameter, height, relative density of stocking, and volume, as well as the best average indicators of health condition and Kraft classes as compared to stands in sections with low (15 %) and heavy (29%) intensities of thinning.

The moderate intensity of thinning in oak stands allows achieving the maximum yield of timber assortments obtained from trunks of larger diameters, such as barrel logs, fineline veneer, and sawlog.

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