Making the case for planning and investment in green infrastructure: a case study of street trees and property value impacts in Brisbane, Australia

Abstract

Trees in cities grow closest to where people live, work and travel, and offer a wide range of ecosystem services (ES). Emerging urban forest research has focused on helping communities and urban tree managers build awareness of the connections between urban forest structure, ES and the quality of human life in rapidly growing cities. Yet translation of the proliferation of urban ES scholarship to urban forest policy, planning and investment has been inconsistent. This study focuses on the robustness and relevance of measures and values of urban ES being presented to decision makers. Opportunities were identified to improve contemporary techniques for gathering and applying evidence to strengthen the case for strategic planning and investment in street trees. For example, a new approach to pre-stratification in sample survey design to account for unevenness in the density and distribution of street trees across 115 residential suburbs, in the case study city of Brisbane, Australia, was used to confirm that their goal of increasing residential footpath tree shade cover from 35 per cent in 2010 to 50 per cent by 2031 was achievable. A strong case for continuing to invest was also justified by analysing additional data about 2,299 houses that sold between 2008 and 2010, gathered from within the same 80 sample sites as the street tree sample survey. Hedonic price modelling revealed that home-buyers were willing to pay a premium for houses with 35 per cent street tree cover nearby. These premiums translated to annual property value benefits that exceeded annual costs of street tree planting and maintenance in Brisbane in 2009-10 by a ratio of between 2.06 and 2.2:1. Returns of almost AU$1 million per year to the local government and an additional AU$1-1.2 million per year to the state government in property tax revenues were also identified. This approach advances the broader use of ES valuation as both a business case development and policy revision tool. However, results of a preliminary survey of four international cities, Sacramento (USA), New York City (USA), London (UK) and Melbourne (Australia) who had made significant investments in major street tree planting projects in the last 10 years, suggest that structural measures and ES valuations are a subset of a range of robust and contextually relevant inputs to making the case for planning and investing in urban forests and green infrastructure.