Health condition of natural oak stands in the Left-Bank Forest-Steppe of Ukraine

Abstract

Introduction

In recent years, several regions of Ukraine have experienced forest weakening and dieback, including oak forests, primarily due to the combined effects of abiotic, biotic, and anthropogenic factors. Assessing the health condition of forests, particularly natural oak stands in the Left-Bank Forest-Steppe of Ukraine, is therefore essential for predicting stand decline and for improving forest management practices aimed at enhancing stand resilience and productivity. The aim of this study was to analyze the dynamics of the health condition of coppice-origin and natural seed-origin oak stands and to assess the degree of their degradation under the influence of various environmental and anthropogenic factors.

Materials and Methods

The health condition of oak trees was evaluated on four permanent and 32 temporary sample plots established in natural oak stands of different ages in the Sumy and Kharkiv regions, following standard forestry and forest inventory methods

The studied stands were 85–200 years old, with a relative density of stocking of 0.5–0.9. The proportion of oak in the first canopy layer ranged from 40% to 100%, and stand origin included both coppice and natural seed regeneration. Stand health and damage intensity were characterized using the mean health condition index (І_с). Tree health was classified according to the condition category scale defined in the Sanitary Forests Regulations in Ukraine.

Results

On permanent sample plots, the mean health condition index of natural oak stands ranged from 1.27 to 1.81, while that of oak trees specifically ranged from 1.59 to 1.82. These stands were classified as “healthy” and “weakened”, with damage intensity assessed as “none” to “low”. A slight deterioration in health condition was observed with increasing stand age.

A relationship was identified between stand health condition and species composition. The poorest health condition (І_с = 1.81) occurred in nearly pure oak stands with only a minor admixture (up to 5% of growing stock) of common ash. Increasing the proportion of associated species (common ash, small-leaved lime, and Norway maple) to 50–60% improved stand health (І_с = 1.27–1.54). Oak trees in health categories 1 and 2 predominated, accounting for 86–92% of the total trees.

On temporary sample plots, the mean health condition index ranged from 1.65 to 2.56 for stands overall and from 2.02 to 2.94 for oak trees. These stands were classified as “weakened” to “severely weakened”, with damage intensity increasing from “low” to “moderate” with stand age, depending on species composition. Stands with 80% oak trees exhibited better health (І_с = 1.65–2.43) than those with 90% oak trees (І_с = 1.89–2.56). The proportion of standing dead trees was low, not exceeding 16% of the total oak growing stock.

Conclusions. Natural oak stands in the Left-Bank Forest-Steppe of Ukraine were generally characterized by a relatively good health condition. In stands of various ages and compositions, trees in health condition categories 1 and 2 predominated, accounting for more than 80% of all trees, while the proportion of standing dead trees remained low.  Overall, these findings indicate no clear evidence of oak stand degradation in the region. To further improve the health and stability of oak stands, targeted tending and sanitary felling should be implemented, with a focus on optimizing stand composition and enhancing resilience.

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