Microclimatic effects of introduced tree plantings in urban environment

Ecological role of urban green spaces is increasing in order to provide citizens with comfortable and safe living conditions in the new climatic realities through the use of ecosystem services of tree and shrub stands in the setting of reduced forest areas, native forest decline and acceleration of urbanization processes. However, in Europe and, in particular, in Ukraine, deterioration of the environmental condition and loss of ecological functions of urban green spaces are observed. One of the reasons for the loss of ecological potential of tree and shrub plantings is unbalanced approach to the development of green infrastructure in cities, when socio-cultural ecosystem services (decorative, aesthetic) are preferred over environmental and regulatory ones, including over climate-regulating services. The active use of introduced tree species has always been driven by the development of green infrastructure in modern cities; the share of these species in dendroflora of urban ecosystems is steadily increasing in Europe. Introduced tree species comprise the basis of urban green infrastructure; therefore, the issue of determining the potential microclimatic effects of these species becomes relevant. The influence of tree species (Acer pseudoplatanus, Fraxinus pennsylvanica, Gleditsia triacanthos, Morus alba, Quercus rubra, Robinia pseudoacacia, Tilia platyphyllos) introduced in the Steppe zone of Ukraine on the formation of microclimatic parameters (light intensity, temperature and relative air humidity) in the space beneath the tree canopy within monodominant group plantings is analyzed in Botanical Garden of Oles Honchar Dnipro National University and park areas of Dnipro city. Beneficial effect of group plantings consisting of introduced tree species on the processes of optimizing the microclimatic conditions of the urban environment is revealed. Beneath the canopy of introduced tree species (compared to the reference open sites), light intensity decreased from 86.9% to 97.9% at midday in late July. The air temperature decreased from 3°C to 6.5°C, and the relative humidity increased by 2.5–9.8%, depending on the species of the tree. By increasing the microclimatic efficiency, the studied tree introducents were determined to form the following series: Gleditsia triacanthos – Robinia pseudoacacia – Fraxinus pennsylvanica – Quercus rubra – Tilia platyphyllos – Acer pseudoplatanus – Morus alba. Along with a significant climate-regulating effect, monodominant group plantings consisting of dense- and semi-dense crowned introduced tree species become "cooling islands" and play a significant role in optimizing the microclimatic conditions of urban ecosystems during the daytime and summer periods. At the same time, introduced tree species with naturally developed dense and semi-dense crowns can be prioritized for creating and reconstructing green spaces with recreational purposes in the cities situated in Steppe zone. The results obtained regarding the microclimatic effects of introduced tree species expand the scientific and theoretical base for the development of methods for optimizing the functionality of green infrastructure in cities by the construction of green spaces using tree species that have significant climate-regulating properties.