Influence of the Urban Heat Island Effect of a Large City on the Physiological Stability of Tree Plantations

Lviv (Ukraine), a city of about 1 million inhabitants, is classified as a Western Forest-Steppe according to the forestry zonation. The mesoclimatic anomaly in the western forest-steppe with its humid mild climate is composed of the sum of microclimates formed by the thermal regime. As in every large city, Lviv has historically developed a distinctive microclimate influenced by many natural and anthropogenic factors, including global climate change, urban development, population growth, landscape fires, etc. This contributes to the development of a heat island effect, which is characterised primarily by an increase in air temperature and a decrease in air humidity and is a negative factor for the development of vegetation in the city’s green zone. It was necessary to investigate the territory of the “dry island” – the lower tier of the “heat island” – to determine the level of vitality of the main woody plants located within these boundaries. As it could be observed, the “dry island” is located in the dense development of the central part of the city, where the temperature of the dead underlying surface (stone, asphalt, concrete) was in the range of 57–62 °C, the air temperature was 28.5–29.1 °C, and the humidity was 50.2–51.2%. Drought conditions affect the growth, development and reproductive capacity of woody plants. It has been established that the heat island should be reduced by urban greening in the horizontal and vertical ranges, and to maintain the physiological stability of tree plantations in the hot season, it is necessary to develop recommendations for the care of vegetation in the green zone of the city, depending on microclimatic indicators, especially air and soil temperatures, air and soil humidity.