Stock structure in oak stands of different origin under the conditions of the Left-Bank Forest-Steppe of Ukraine

Abstract

Introduction

The condition, structure and productivity of pedunculate oak (Quercus robur L.) stands in the Left-Bank Forest-Steppe of Ukraine remain an important research issue. Oak stands managed by the State Enterprise “Forests of Ukraine” in this region cover approximately 285 thousand ha. Given the importance of assessing the dimensional and qualitative structure of these stands under current conditions, systematic studies are required. The aim of the study was to determine the dimensional and qualitative structure of planted and coppice-origin oak stands.

Materials and Methods

The study was conducted on 20 temporary sample plots (TSPs) located in the Trostianets (Sumy region) and Huty (Kharkiv region) forestry management units. Sample plots were established in the dominant forest types, taking into account stand origin and productivity, in accordance with standard forest mensuration methods. The dimensional and qualitative structure of the stands was assessed using commonly accepted standards. Oak and ash on TSPs 1–5 were of planted origin, whereas on TSPs 6–20 they were of coppice origin; the associated species were of mixed (seed and coppice) origin. On TSPs 10, 14, and 15, a considerable proportion of oak stems was of seed origin. The average age of oak stands ranged from 95 to 126 years.

Results

The distribution of stems by technical suitability categories and the yield of timber by quality classes were evaluated. The average proportion of merchantable stems was 30.4 ± 1.5%, and the proportion of merchantable timber was 38.2 ± 2.4%. In planted stands, the share of merchantable stems averaged 27.4 ± 1.2%, including oak – 70.5%, ash – 27.4%, Norway maple – 7.6%, and small-leaved lime – 14.5%. In coppice stands, the proportion of merchantable stems averaged 31.4 ± 2.0%, with a lower share of oak (67.5%) and higher shares of associated species (ash – 55.4%, maple – 13.7%, and lime – 31.6%). The proportion of merchantable timber amounted to 38.6 ± 1.5% in planted stands and 38.1 ± 2.8% in coppice stands. The proportion of quality class A timber was 4.0% in planted stands and 2.9% in coppice stands, with a maximum value of 6.7%. According to diameter classes, more than 34.5% of timber volume consisted of logs with diameters of 30–39 cm, 26.0% – 40–49 cm, and 21.8% – 20–29 cm. A tendency toward an increase in the share of merchantable timber was observed in stands containing 70–80% oak. The obtained merchantable timber yield (38%) corresponds to the results of previous studies, which reported 40–42% in coppice-origin stands aged 100–110 years with diameters of 34–36 cm, as well as a proportion of large-diameter merchantable timber of 70–75%. The largest share of timber belonged to quality class D (66.0% in coppice stands and 56.7% in planted stands), whereas class C accounted for 22.7% and 30.2%, respectively; the proportions of the remaining quality classes were insignificant. The actual yield of quality classes A and B in harvesting areas was slightly lower because of hidden defects, especially in coppice-origin stands.

Conclusions

The dimensional and qualitative structure of oak stands is primarily determined by stand density, species composition, mean diameter and height, and stem quality. The optimal composition of mature stands is represented by mixed stands containing about 80% oak and 10–20% associated species, particularly ash, which ensures higher productivity and improved timber quality. Given the predominance of coppice-origin stands in the region, regeneration fellings should focus on the formation of seed-origin stands, which are characterized by greater longevity, stability, and timber quality, while maintaining an admixture of associated species in accordance with forest site conditions.