Urban vegetation : towards cooler, biodiverse cities of the future

Abstract

This thesis presents my doctoral research programme that aims to increase the understanding of the role that vegetation plays in functional urban ecosystems. To do this, I have systematically evaluated: (1) relationships between tree canopy traits and associated subcanopy cooling; (2) how planting context (e.g., parks or streets) influences the ability of trees to provide cooling benefits; (3) how canopy-associated cooling is influenced by ambient climatic conditions (solar radiation, vapor pressure deficit (VPD) and wind speed); and (4) how habitat/vegetation complexity influences invertebrate biodiversity, in urban settings across Greater Sydney. Whilst there has been some research exploring relationships between vegetation and landscape traits and urban temperature profiles, to date no study has systematically evaluated how different planting contexts, such as parks, nature strips or pavement/tarmac settings, influence the ability of trees to provide cooling benefits in the local environment. To address this gap, my research identifies those traits that determine the cooling potential of urban trees, alongside the impacts of planting context on the ability of trees to reduce air and surface temperatures. The first data chapter presents the results of a study across Greater Sydney that found tree shade reduced air and surface temperature by a maximum of 3.7 °C (mean 1.1 °C) and 45 °C (mean 27.4 °C), respectively. The magnitude and variability of tree-derived cooling benefits differ greatly among studies, likely reflecting differences in tree species' traits, urban characteristics and local climate conditions. The second data chapter presents findings from a systematic study focused on ten commonly occurring species in western Sydney. In addition to the cooling benefits provided by trees, urban vegetation also provides other critical ecosystem services, including habitat and resources for a diverse range of vertebrate and invertebrate animal species. For example, an invertebrate-rich environment xi contributes to food security, nutrient cycling and pest control. Systematic explorations of the association between habitat/vegetation complexity and invertebrate biodiversity in urban areas are limited. My third data chapter therefore examined whether and how trees and shrubs differ in terms of the diversity, abundance and composition of associated invertebrate communities. Overall, my thesis research provides valuable new insights into the extent of cooling benefits provided by a variety of tree species in urban areas throughout Greater Sydney, and how these are influenced by tree canopy traits and local environmental conditions.

Date of Award	2022
Original language	English