The ecosystem disservices of trees on sidewalks: A study based on a municipality urban tree inventory in Central Italy

Urban green infrastructure, including street trees, plays a key role in providing ecosystem services to urban residents. However, to fully understand the effective role of trees in the urban context, it is also necessary to evaluate the disservices that they can produce in the development of their functions if not managed in an adequate and integrated way. This contribution aims to demonstrate an approach to assess three disservices (pavement damage, aesthetic damage, likelihood of tree failure) of street trees at the municipal level, starting from the existing municipal tree inventory. In this case study, from the street tree population, a sample of approximately 5% of the trees was drawn by stratified random sampling, where the strata were composed of groups of tree species. In particular, a sampling scheme is adapted in which the probability to select a tree in the sample is greater for bigger trees, under the assumption that the bigger the trees the greater are the disservices caused. In this way, a greater precision of the estimates of the considered disservices for the population of urban trees is expected. The results show a high variability of disservices provision among species groups. The results also confirmed a positive correlation between the considered disservices and tree diameter at breast height, while other tree attributes such as total height and crown diameter were found to be positively related only to pavement damages. Finally, severe pruning can lead to a high level of the aesthetic and functional disservices even for shorter and younger street trees.