COS 315-2 - Measuring the social and ecological contributions of urban trees: insights from two tree-removal experiments

Abstract: Many world cities are looking into planting and retaining more urban trees to provide critical ecosystem services. However, cities often struggle to articulate the social and ecological benefits of urban trees (i.e., specific effects of urban trees on people and wildlife). Advances in urban social-ecological research are needed to understand the combined social and ecological benefits of urban trees. Most of the evidence on the benefits of urban trees is correlational, specifically, associations of urban tree abundance (e.g., canopy cover, tree density) and selected biodiversity (e.g., abundance and diversity of birds) and social (e.g., self-reported levels of subjective wellbeing) calculated at one point in time over large scales (e.g., whole city). Experimentally manipulating the abundance and diversity of urban trees, such as increasing or decreasing the amount and/or density of urban trees, can help demonstrate the complex interactions among biodiversity, humans, and urban trees over time, and generate important evidence on the social and ecological contributions of urban trees. In this presentation we report results from tree-removal experiments undertaken in Melbourne, Australia, and Toronto, Canada. The experiments answered two research questions: 1) how does the removal of urban trees affect the abundance and diversity of ecological communities?; and 2) how does the removal of urban trees affect people’s perceptions of and behaviours around urban trees? We designed two experiments, one in an urban park, and on in a suburban woodlot, where tree removals were occurring. We collected ecological (i.e., abundance and diversity of various taxa, including birds and mammals) and social (i.e., perceptions associated with urban trees; people’s movements using innovative GPS tracking data) data at these field sites as well as from similar sites for control. We analysed these data to determine the combined effect of before/after urban tree removal at impact/control sites on changes in wildlife abundance and diversity, as well as people’s perceptions and behaviours. With this study we generate complementary evidence that urban trees provide critical habitat to urban wildlife and are of critical importance to people’s nature experiences, and demonstrate how these social-ecological effects are scale and context-dependent.