Understanding the carbon and pollution mitigation potential of Australia's urban forest: final report

Horticulture Australia Ltd
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2013, pp. 1 - 89
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The urban forest holds a particular role in the Australian urban landscape. A mixture of remnant, native and exotic trees, it is managed by a variety of government and private actors, existing at once as an expenditure for local authorities while providing a range of unquantified benefits such as habitats for wildlife, air pollution removal and flood prevention. Despite its prominence as an identifier for an urban area or as the backdrop in the lives of urban residents, the urban forest continues to be undervalued as part of the policy process. In response to a renewed need to appraise the benefits of the urban forest in the face of climate change, the aim of this project was to contribute to the development of tools that help value the urban forest, while seeking an understanding of the feelings of residents towards urban trees. Our study focuses on two corridors both 400 m wide: 11 km along the Parramatta Road and 19 km along the Pacific Highway and both cutting through a variety of different suburbs in Sydney. We analysed the benefits of the forest using the i-Tree methodology and also through the use of remote sensing with Light Detection and Ranging (LiDAR).We also gained the residents views about the trees in North Sydney and Parramatta Local Government Authority areas, targeting a survey of 1500 residents who responded with a 819% response rate. The results of the i-Tree method reveal that the estimated population of 30,500 trees in the Pacific Highway corridor alone, deliver a combined annual benefit of $97,770 per year from carbon sequestration, air pollution removal, building energy savings and avoided carbon emissions, while storing an estimated $1.65 million of carbon (at $23 per tonne). At the same time, the study reveals marked differences in the species distribution between the two roads and the benefits delivered from an individual tree. These benefits vary because of the dominant species and its age and height. The LiDAR component of the study reveals the detail in the species composition enabling the identification of allergenic species or those vulnerable to disease such as myrtle rust. It also highlights that the trees reduce the incident radiation in the corridors by between 8 20% depending on the time of year. Finally, the survey results show that residents in both areas are favourably disposed towards further tree planting on streets that already have trees and value the appearance of the trees on their own property, while being aware of other benefits such as shading and the need to remove trees only where it will damage paths or house foundations. The biggest difference between the two areas are revealed in opinions about the lack of trees with 69% of North Sydney respondents answering that there were not enough trees but only 24% of respondents in Parramatta local government area answering the same. Overall, the study is the first of its kind in Australia. It compares two leading methods for understanding the benefits of the urban forest in Australian cities and provides a benchmark for the application of these techniques in other cities and regions.
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