PhD Oral Exam - Lingshan Li, Geography, Urban and Environmental Studies

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

In response to the need for ecologically informed urban green space planning and design, the overall objective of my thesis is to evaluate how spatial patterns of urban green infrastructure (UGI) influence ecosystem service provision across various spatial and temporal scales. My first chapter explored the impact of UGI’s spatial pattern on land surface temperature and its corresponding distributional inequity. My results show that aggregated tree clusters offer greater cooling benefits than fragments or dispersed green spaces during the day, especially at a larger spatial scale. Mapping mismatches in cooling supply and demand revealed that neighborhoods with higher proportions of visible minorities and low-income residents had significantly lower access to cooling services. My second chapter examined the effects of different spatial configurations of vegetation on microclimate conditions. The results indicated that aggregate tree clusters had stronger cooling effects than discrete tree clusters during daytime, but inhibited heat dissipation at night. However, relative humidity exhibited an inverse pattern compared to air temperature, moderating wet-bulb temperature differences among vegetation configurations. My third chapter assessed how tree cluster arrangements (linear vs. grouped) influence NO₂ and O₃ concentrations within urban parks. No significant differences in NO₂ concentrations were observed on either side of the tree clusters regardless of whether trees were planted in linear arrangements or grouped configurations, showing trees did not act as barriers to NO₂ dispersion. A slight “trap effect” of trees on NO₂ concentrations was detected, while there was a significant decrease of O₃ concentrations under tree clusters of both configurations.