Synergies and Trade-offs in Urban Green Infrastructure

Abstract

Urban Green Infrastructure (UGI) is increasingly integrated into urban planning to tackle climate change, biodiversity loss, and public health challenges. Its multifunctionality and ability to deliver multiple Ecosystem Services (ESs) make UGI a "win-win" nature-based solution. Yet, focusing only on benefits risks overlooking Ecosystem Disservices (EDs) and the trade-offs from competing goals. This thesis advances a multidimensional, causally informed understanding of how synergies and trade-offs in UGI are conceptualised in research and practice. It addresses four questions: how these synergies and trade-offs are conceptualised; how they are represented and assessed in studies; how plant functional traits influence them; and what synergies and trade-offs exist between UGI policy objectives and stakeholder perceptions in Canberra, Australia. A tripartite analytical framework is developed to explain synergies and trade-offs as outcomes shaped by three interconnected dimensions: biophysical processes, sociocultural values, and policy priorities. Moving beyond simple correlations between ESs and EDs, the framework serves as a diagnostic tool to identify causal mechanisms and context-specific dynamics. A mixed-methods design operationalises and tests the framework. First, a systematic review of 96 global studies shows a dominant focus on biophysical outcomes and a reliance on statistical bundling of ESs and EDs, offering limited explanatory power. It highlights the potential of functional trait analysis as an underused method to identify ecological drivers of ESs and EDs and improve causal inferences. Building on this, the first case study uses functional trait analysis to examine synergies and trade-offs in microclimatic benefits, Urban Heat Island (UHI) mitigation and thermal stress reduction, provided by four morphologically distinct urban tree species in Canberra. Results show trait-service relationships are highly context-dependent. Factors such as solar irradiance, seasonality, and surface material affect cooling benefits. Traits like crown density consistently deliver synergistic benefits, while others create trade-offs under varying solar conditions. These findings demonstrate the diagnostic value of trait analysis but caution against universal trait prescriptions, calling for locally adapted planning. The second case study explores sociocultural and policy dimensions through thematic analysis of legislation, policy documents, and stakeholder submissions to a Canberra urban forest inquiry. While legislation is cohesive, policies and stakeholder views diverge. Policies emphasise city-wide canopy expansion for biodiversity and UHI mitigation, whereas stakeholders highlight concerns such as property damage and personal safety. These differences reveal potential mismatches and trade-offs between policy goals and community expectations, and even among policymakers themselves. The study underscores the need for proactive, inclusive engagement to achieve socially sustainable UGI outcomes. Overall, the research confirms that synergies and trade-offs are shaped not only by ecological factors but also by sociocultural values and policy priorities. The tripartite framework offers both theoretical and practical advances for diagnosing and navigating complexity in UGI planning. It contributes to global debates by promoting an integrative, reflexive approach to planning UGI that is ecologically effective, socially inclusive, and institutionally viable. Show more