Features of forest mensuration characteristics and health condition dynamics in Prydonetsky Steppe of Ukraine: Climate change context

Abstract

Introduction

Climate change has been leading to significant shifts in the boundaries of bioclimatic regions of the Earth. Forest stands became more vulnerable and less resistant to biotic damage, they reduce their productivity and decline.

The aim of the research was to identify the features of both the forest fund structure and mensuration indicators dynamics for the forest stands in Prydonetsky Steppe, Ukraine (on the example of Lyman State Forest Enterprise) in the context of climate change.

Materials and Methods

Two forest stand-wise inventories (2005 and 2020) and the project of forest management in Lyman State Forest Enterprise (2021) were used as source data for forest evaluation. The dynamics of the pine stands health condition was assessed according to the I Level forest monitoring carried out in 2005–2021. The data from ClimateCharts.net for the region of the study were used to calculate climate indicators, such as average annual air temperature, precipitation, and hydrothermal coefficients according to Vorobyov, hydro-thermal coefficient of Selyaninov, de Marton index for 30-year and 10-year periods.

Results

Over the past 30 years, climate warming in the Prydonetsky Steppe of Ukraine caused a temperature growth by 0.8°C, with the highest rate of warming over the past 20 years. Over the recent decade, the climate has changed to a very dry relatively warm climate, due to a significant increase in air temperature (by 0.8 °C), and a significant decrease in precipitation amount (by 10%), in particular during the growing season, which has led to a moisture deficit in the region, decreasing, at that, groundwater level, which is unfavorable for woody vegetation.

The forest stands of the enterprise are typical for the region: Scots pine (Pinus sylvestris L.) (57.4% of the area) and English oak (Quercus robur L.) (17.8%) stands prevail. Compared to 2005, the total forested area of Lyman State Forest Enterprise increased by 690.1 hectares (2.8%) in 2020, mainly due to both land use changes and soil and climatic factors, resulting from overgrowing of dried wetlands with woody vegetation. During only 15 years, unfavorable hydrological and climatic factors as well as fires, pests, and diseases caused the mortality of 460 hectares of pine forest in the region, mainly due to sanitary felling in weakened and declining stands. Meanwhile, the area of deciduous species such as English oak, common ash, and black alder, as well as introduced species such as black locust (Robinia pseudoacacia L.), ash maple (Acer negundo L.), and shrubs (European smoketree) has increased.

For the period 2005–2010, the Scots pine defoliation index increased by an average of 5.0%; during 2015–2021 its growth continued, by 8.3%. In 2021, a significant weakening and dieback of pine stands in the Lyman State Forest Enterprise were observed due to increased adverse conditions and damage caused to weakened stands by stem pests.

Conclusions

Climatic data indicate a tendency towards warming and aridization of habitat conditions.

During 2005–2020, the area of pine stands and their density of stocking decreased, while the area of deciduous species: oak, ash, alder (black), as well as black locust, ash maple (introduced species) and shrubs such as European smoketree increased. Drying of wetlands and their overgrowing with deciduous forests was also detected.

Monitoring data point to a long-term trend toward the deterioration of pine forests. The maximal defoliation values were observed in 2021, which indicates the weakening of pine trees.

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