Expert views on species selection for urban tree planting

Abstract

Urban trees contribute to better human health by providing shade and regulating urban temperatures, improving air, water and soil quality, reducing noise pollution, and providing a space for recreational and physical activities to take place. However, urban areas are challenging environments for ensuring the well-being of trees as there are heavy pollution concentrations, limited space above and underground, impermeable surfaces affecting the hydrological cycle, heavy construction and elevated temperatures. Climate change is only making these environments more challenging with increased severity and frequency of floods, droughts and heatwaves. Therefore, it is important to gain better insight into the factors that affect what tree species are to be planted in these places by identifying expert knowledge on the subject. This project aimed to widen the knowledge of urban stressors affecting trees in Southwestern Sweden as well as the best suited tree species to withstand such stressors by introducing an expert perspective who have practical experience in the field of urban trees. This project also seeked to provide some insight into which tree characteristics influence the choice of tree species in urban environments. Data was collected through an online survey addressed to Swedish experts that have practical experience working with urban trees. A list of 17 common urban species in South-western Sweden were selected to study. Out of this group, species deemed highly suitable for park environments were Fagus sylvatica and Quercus robur while Ulmus minor and Pinus nigra were best suited for street environments. Species deemed very ill-suited for street environments were Aesculus hippocastanum and Fagus sylvatica while Picea abies and Betula pendula were the least suited species for park environments. Drought and heatwaves together with soil compaction and available space underground were considered to be the most important pressures affecting the well- being of urban trees. Tolerance to extreme weather environments and disease tolerance were the most significant considerations in the selection of street trees while contribution to ecosystem services affected the species selection process for park environments the most. Experts expressed that there are substantial knowledge gaps within the field. Future research could look into the optimisation of plant bed design and improving understanding on the interaction of newly introduced species with their environment.