Oak stands in the Kharkiv Forest Research Station and features of their natural regeneration

Abstract

Introduction

Natural regeneration of oak (Quercus robur L.) forests is one of the most important issues in forestry, taking into account their value, their performance of important environmental protection functions, as well as providing the country’s economy with high-quality wood.

The aim of the study was to reveal the dependence of the number of seedlings of economically valuable species under the canopy of natural oak stands on the mensuration indicators of parent stands (composition, age, density of stocking) for further successful regeneration of mature and overmature oak forests by seeds in the Left-Bank Forest-Steppe.

Materials and Methods

To carry out the study, we analysed forest management materials (as of 01.01.2017) and estimated the distribution of the area and stock of the oak stands by forestry and mensuration indicators.

The quantitative status of seedlings of economically valuable species was studied during 2020–2021 under a canopy of mixed oak stands of natural origin aged 80–145 years in fresh fertile site conditions. The relative density of stocking made 0.5–0.9, and the proportion of oak in the stand composition was 80–90%.

We recorded the seedlings in circular plots (10 m² each). The degree of success of natural regeneration was evaluated according to the scale designed in the Ukrainian Research Institute of Forestry and Forest Melioration. During the evaluation, attention was paid to the amount of undergrowth in terms of both age and height groups, as well as to its abundance.

Results

The study showed that under the canopy of natural oak stands of different ages, compositions, and densities of stocking, growing in the fresh fertile sites, the most active natural regeneration of economically valuable species takes place in older stands, in particular in overmature ones. Such stands have the best conditions for the natural regeneration of the main species: the sparse canopy of the parent stand provides undergrowth with a sufficient amount of light and heat. Thus, the number of seedlings of economically valuable species in them reached 26.4 thousand per hectare, including up to 1.9 thousand seedlings per hectare of English oak.

The insignificant proportion of oak in the composition of the previous regeneration, represented mainly by sprouts and a small share of weak 2–3-year-old seedlings, was a result of very poor oak fruiting during 2016–2021. The regeneration success in all the studied areas was defined as “poor”.

The seedlings of both English oak and small-leaved lime have a group placement at the plot, those of wych elm occupy the territory unevenly, and seedlings of common ash, Norway maple and field maple, on the contrary, occupy the territory evenly.

The findings point to the dependence of the seedlings of economically valuable species on the density of stocking in parent stands. Thus, the largest numbers of seedlings were recorded under the canopy of the 80–100-year-old and 101–120-year-old oak stands with a density of stocking 0.7 as well as under the canopy of the 121–150-year-old oak stands with a density of stocking 0.6. As the density of stocking in the stands increases or decreases, the number of seedlings goes down.

Conclusions

It is advisable to take into account the identified features of height and the age structure of seedlings of economically valuable species as well as the nature of their location at the plots when selecting areas of old (mature and overmature) oak stands for their further natural seed regeneration.

In such stands, it is reasonable to widely introduce activities aimed at promoting their natural regeneration, taking into account at that the oak fruiting cycle.

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