Urban forest vulnerability and its implications for ecosystem service supply at multiple scales

Abstract

The urban forest is a valuable ecosystem service provider that is garnering increasing attention in environmental research and municipal planning agendas. However, because of its location in heavily built-up and densely-settled environments, the urban forest is vulnerable. The purpose of this dissertation is to conceptualize, assess, and analyze urban forest ecosystems and their vulnerability at multiple spatial and temporal scales. An urban forest ecosystem classification framework that integrates biophysical, built, and human components is developed. Subsequent classification of ecosystems at the neighbourhood scale reveals the spatial arrangement of several social-ecological interactions. Such information is valuable to ecosystem-based decision support while also informing future vulnerability research. The investigation of ecosystem vulnerability began with the development of a theory-based conceptual framework. Urban forest vulnerability is defined as the likelihood of decline in ecosystem service supply and its associated benefits for human populations, urban infrastructure, and biodiversity. It is comprised of exposure, sensitivity, and adaptive capacity, which describe the built environment and associated stressors, urban forest structure, and the human population, respectively. This framework is applied using empirical field research in Toronto, Canada to explore the processes of vulnerability and their influence on ecological change. Results indicate that there are several significant predictors of urban forest decline and mortality, and emphasize the importance of applying diverse metrics to describe the built environment and urban forest structure at fine spatial scales. Vulnerability assessment and analysis at much broader spatial and temporal scales, using a spatially-explicit assessment approach and ecological modelling of alternative management and disturbance scenarios, is further investigated. This latter research emphasizes the importance of aligning scales of management with ecosystem function and the long-term influence of management intervention on ecological conditions. The multiple scales of investigation and methodological approaches developed in this study provide complementary opportunities to synthesize and apply existing theory in novel settings while also generating new theories pertaining to the processes of urban ecosystem change and decline. The intention of this study is to contribute to the understanding of urban forest ecosystems and their vulnerability, while also providing practical knowledge and tools for the sustainable management of this resource.