Variation in ecosystem services of street tree assemblages can guide sustainable urban development

Urban afforestation is an important strategy for promoting sustainable urban development. In cities where large new green spaces are not available, the planting of curbside trees is deemed to be an important afforestation strategy. However, variations in the ecosystem services provided by street tree assemblages across socioeconomic gradients have been underexplored. We examined such variations in ecosystem services provided by street tree assemblages along an urban-suburban continuum. Our findings were as follows. (1) Not all ecosystem services showed increasing trends along the urban-suburban continuum. Some ecosystem services at the street tree assemblage level, such as air purification and rainfall interception were prominent in areas of high urbanization intensity. (2) Diverse ecosystem service trends were found in relation to differential characteristics of street trees assemblages. Structural properties of street tree assemblages, such as tree density and age structure, are likely key factors influencing variations. (3) Although street tree density could partially compensate for the loss of large old trees, the protection of such trees is important because of their close associations with key ecosystem services, such as total carbon storage. To maximize the value of street trees in promoting urban sustainable development, trade-offs among multiple ecosystem services should be integrated within the overall planning process and adjustments of planting regimes.