Towards an evaluation of the local scale health and climate related ecosystem services of street trees

Urban tree planting programmes are being encouraged to improve the sustainability of urban centres and to enhance human health and well-being. Space constraints mean that in many cities opportunities for planting may be... [ view full abstract ]

Urban tree planting programmes are being encouraged to improve the sustainability of urban centres and to enhance human health and well-being. Space constraints mean that in many cities opportunities for planting may be limited to kerbside locations. However, the net impact of (street) trees on human health and the environment at local scales is not clear and generalised approaches for evaluating their impacts are not well developed.

We use an urban ecosystems services framework to evaluate the direct, and locally-generated, ecosystems (dis)services provided by street trees. We focus our review on the services commonly used to justify new street tree or street tree retention initiatives. These include ‘climate and air quality regulation’ and ‘aesthetics and cultural services’. We argue that current scientific understanding of the impact of trees on climate and health in the urban environment has been limited by reductionist regional-scale approaches. These often consider vegetation generally and/or single out individual ecosystem (dis)services without considering the wider synergistic impacts on urban ecosystems. This may result in planners and policymakers leaning towards ‘single parameter optimisation’ decision making strategies. This may be problematic when a single intervention (such as street tree planting) offers different outcomes and has multiple effects and potential trade-offs in different places.

We argue for a multi-scale, holistic approach to evaluate the (dis)services provided by street trees. We demonstrate the importance of identifying the specific aim of the intervention, the scale of the desired biophysical effect and an awareness of a range of impacts when choosing i) tree species, ii) location and iii) density of tree placements. We offer suggestions to guide decision makers and planners towards the strategic use of street trees as an effective tool in developing resilient and resourceful cities in the current era of climatic change.