Abstract:
Rapid urbanisation and increasing population density are resulting in land use change and degradation of the urban environment. Urban greenspaces are a critical tool for mitigating the negative environmental effects of urbanisation. However, there is still limited information regarding how the structure and function of urban greenspaces affect ecosystem function and the mitigation potential of urban greenspaces. Thus, the overall aim of this thesis was to quantify the structure and function of urban greenspaces in Auckland. Leaf Area Index is a key structural characteristic of forests because it influences many biological and physical processes in plant canopies. The following research questions were investigated: (1) What is the magnitude and seasonal variability of Leaf Area Index (LAI) of open-grown and closed-canopy urban greenspaces? (2) How do different methods measure LAI in a mixed Urban Forest? (3) How does species composition affect the magnitude and variability of LAI? This study found LAI of Auckland open and closed grown trees ranged from 2.64 - 5.59 depending on the site and method and LAI decreased by up to 25% during the winter months. Additionally, this study found forest composition influenced the LAI index and its seasonal variability. In a mixed evergreen-deciduous forest, variation is driven by deciduous species, whilst the evergreen species present dampen seasonal effects. However, neither litter fall measurements nor hemispherical estimations are ideal methods for a mixed forest without additional measurements on leaf phenology. i-Tree Eco is a model developed in the U.S. for quantifying the structure and ecosystem services of forests. However, i-Tree Eco still requires validation for New Zealand application. The following research questions were investigated: (1) How do i-Tree Eco estimates for carbon storage and Leaf Area Index compare to on site measurements of Leaf Area Index and carbon storage derived from local allometric equations? (2) How does the forest structure and ecosystem services differ between Parkland and Urban Forest in the Auckland Domain? (3) What are the implications of forest management on ecosystem function? This study estimated the ecosystem services for the Urban Forest (13.8 ha) and Parkland (10.8 ha) in the Auckland Domain and provided an evaluation of the differences between two management strategies. The Urban Forest was found to store 216 t ha-1 of carbon and sequestered 9.6 t ha-1 yr-1. The Parkland stored 171 t ha-1 of carbon and sequestered 4.8 t ha-1 yr-1. Despite a lower tree density in the Parkland, the larger trees were able to store a substantial amount of carbon in fewer trees, and remove a greater amount of pollution per year. A few large trees have much greater potential for mitigating negative environmental effects than several smaller trees, nonetheless, benefits other than ecosystem services need to be considered when designing urban greenspaces. This study has highlighted the potential i-Tree Eco has as a tool for designing and planning New Zealand urban greenspaces, however, more species specific information is needed to improve i-Tree Eco estimations. This study has contributed towards the understanding of Auckland urban greenspaces by providing quantitative evidence to support the validation of the i-Tree Eco model and demonstrating the ecosystem services they produce. The quantification of urban greenspaces is essential to developing sustainable cities.