The research is assessing the physiological and locational suitability of tree species in the urban area of the Municipality of Ljubljana, with the aim of creating an empirical model to support decision-making in urban tree planting. The main research challenge was to create a model that includes key impacts on the health of citizens and physiological parameters, such as insolation, soil pollution, the proportion of green areas and the allergenicity of trees. The analysis is based on the database of the existing urban tree cadastre and a statistical analysis of a sample of 400 trees. Based on the synthesis of physiological requirements and impacts on people, assessments of the suitability of existing plantings were calculated and more optimal tree species were identified for individual areas of the city. The results of the research, which included 40,423 trees, showed that the cadastre achieves 50.20% suitability for all the growing sites of all trees, of which the highest is for trees of the genus Tsuga. In the assessment of the optimal tree composition for the urban environment, the most suitable species are those that demonstrate high tolerance to abiotic factors of the urban environment, such as soil compaction, limited space for the root system, air pollution and high temperatures. These include maples (Acer spp.), poplars (Populus spp.), plane trees (Platanus x hispanica), hornbeams (Carpinus betulus), horse chestnuts (Aesculus hippocastanum), willows (Salix spp.), cherries (Prunus spp.), lindens, limes (Tilia spp.) and pines (Pinus spp.). The model also highlighted significant deviations between the current state and the optimal representation of some species, such as birches, ash and lindens. Birches are currently almost eight times more abundant than would be optimal given the conditions, while ash is represented in smaller numbers. These discrepancies are based on different ecophysiological properties and characteristics of the planting locations. Through statistical analysis of a randomly selected sample of 400 trees, we discovered a connection between the occurrence of tree damage due to the proximity of infrastructure. The proximity of houses, apartment buildings and blocks of flats are shown to be important factors for the frequency of tree damage, which consequently leads to a decrease in their vitality. Based on the findings, we propose to supplement the suitability model, which would better take into account the complex interactions between growth factors, physiological properties of tree species and urban spatial constraints by increasing the number of parameters.
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