Publication Date

March 2019

It is becoming increasingly important to audit nature-based solutions (NBS) projects to understand their utility in addressing urban sustainability goals. However, the ecological and social complexity of such projects makes it difficult to develop performance indicators. Focusing on specific case studies and specific natural elements could advance this area of research. Urban trees are a vital component of many NBS initiatives. Cities with ambitious tree-planting goals rely on urban revitalization to provide the conditions necessary to grow trees in highly urbanized areas, and in this way deploy NBS projects. We present a conceptual and methodological framework of case-specific performance indicators in the context of NBS projects. This framework addresses the type of parameters, measures, and data that could be considered when assessing small-scale, NBS-inspired, revitalization projects, taking the natural elements of these projects, in this case the trees, as the unit of assessment. Our framework integrates ecological, environmental, and social indicators of tree performance and was developed with the experience gained from on-going, multi-year research projects at two revitalization sites in Toronto, Canada, where street trees grew in engineered sub-surface habitats. The framework includes indicators related to: urban tree ecology; tree characteristics; soils; climate and atmosphere; built environment; tree planting, care, and maintenance; social characteristics of the urban space; and human decisions and governance. This study frames the need for interdisciplinarity and case specificity in the development of performance indicators for NBS projects.