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Title:Green infrastructure and human health: Nature exposure, attention, and well-being
Author(s):Jiang, Xiangrong
Director of Research:Sullivan, William
Doctoral Committee Chair(s):Sullivan, William
Doctoral Committee Member(s):Chang, Chun-Yen; McLafferty, Sara; Edwards, Mary
Department / Program:Landscape Architecture
Discipline:Landscape Architecture
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Green Infrastructure
Human Health
Attentional Functioning
Greenness Exposure
Abstract:The environments we live in play an important role in keeping us ready to face challenges in a competitive, complex, information-rich world. There is growing body of studies showing that having access to nature has positive impacts on people’s attentional functioning, capacity to recover from stressful events and the development of social ties among nearby neighbors. In spite of these findings, many of the studies examining the impact of nature on human health have focused on traditional types of green infrastructure, such as trees and parks. We know little about the effects of other newer types of green infrastructure (e.g. bio-swales) on human health and wellbeing. Moreover, we do not know the extent to which daily variations in exposure to various forms of nature are related to health outcomes. This gap in our knowledge hinders the development of green infrastructure that provides multiple benefits – to human beings and the environment. Identifying the extent to which varying densities of green infrastructure contribute to human health can provide evidence-based guidelines for designer, administrators and other stakeholders. The lack of empirical evidence regarding newer types of green infrastructure and their relationship to human health creates a risk that we missing opportunities to promote public health and protect the environment simultaneously. Green infrastructure is often introduced into urban areas as an efficient and eco-friendly way to manage stormwater and increase bio-diversity. Green spaces that include trees, bioswales, retention wetlands, rain gardens and open green spaces are defined as green infrastructure, which are promising to provide a wide variety of benefits to human living environments. However, we have not accumulated enough evidence regarding the effects of newer types of green infrastructure (e.g. rain gardens and bioswales) on human health and wellbeing. These newer green infrastructure types are important approaches for stormwater management and other ecosystem services, which should not be ignored and cannot be avoided in the development of natural resources in people’s daily living environment. Moreover, most people do not live in completely natural settings. Too many people live with too little exposure to nature on a daily basis. It can be challenging to provide decent access to nature for urban residents. Most of previous findings regarding the health benefits by exposure to green infrastructure have been achieved in laboratory settings or through semi-controlled experiments, which do not reflect the dynamic quantity of people’s exposure to nature in their daily lives. If we do not know the extent to which daily variations in exposure to nature are related to health outcomes, we may risk providing not efficient design of green infrastructure to promote public health. The lack of understanding of various types of green infrastructure and the relationship between daily variations in exposure to nature and health outcomes hinders the development of green infrastructure that can be beneficial to both human well-being and environmental sustainability. In order to fill the gap in our knowledge and promote urban green infrastructure, I have conducted studies to shed a light on the benefits people may get from exposure to different types of green infrastructure, and understand how daily variations of exposure to different forms of nature are associated with health outcomes. This dissertation includes: 1) an experiment examining impacts of different types of green infrastructure on attentional functioning; 2) a study connecting attentional benefits to functional networks in the brain; 3) a survey of the relationship between daily exposure to nature and health outcomes. The objective of the first study was to understand the extent to which three levels of exposure of green infrastructure impact recovery from attentional fatigue. I recruited 43 participants and randomly assigned them to watch one of the three videos that consist of 24 images of urban settings. The only differences among the three videos was the type of green infrastructure featured: one video had no green infrastructure, another had street trees, and the final had street trees and bioswales. I measured participants’ attentional functioning before and after they watched one of the videos and calculated the difference between the before and after attentional tests. Results show a significant difference in the improvement from the first to second attentional test between the group with no green infrastructure compared to the group with trees. The group with trees & bioswales was not significantly different than the other two treatment groups. The purpose of the second study was to clarify the mechanism underlying Attention Restoration Theory and observe the restorative process in action. In this study using functional Magnetic Resonance Imaging (fMRI), I connect the previous attentional tests results to functional networks in the brain. I addressed the following questions: 1) What are the neural correlates in the restorative process of exposure to different green infrastructure types? 2) To what extent are the neural correlations consistent with the actual attention scores from participants who viewed different green infrastructure types? Results identify two pairs of functional connectivity. The first significant level of functional connectivity is between the right lateral prefrontal cortex (rlPFC) and the occipital cortex. Post hoc Tukey tests showed that the rlPFC-rMOG1 connectivity was significantly higher in the Trees group compared to the No GI group and the Trees & Bio group. The second significant level of functional connectivity is between the anterior cingular cortex (ACC) and a cluster in the right middle occipital gyrus (rMOG2). Pairwise post hoc tests revealed that the ACC-rMOG2 connectivity in the No GI group is significantly higher than that in the Trees group and in the Trees & Bio group. This is the first study to observe neural correlates associated with exposure to green infrastructure, which provides us supporting evidence for the proposed mechanism of Attention Restoration Theory. The consistency in the results of the attention tests and the observed functional connectivity is consistent with our hypothesis. The purpose of the third study was to measure the daily exposure to nature and examine the extent to which the exposures predict health outcomes. In this study, I addressed the following questions: 1) To what extent are variations in daily exposure to vegetation density (e.g., in neighborhoods, daily destinations, and routes) associated with human health? That is, do higher levels of daily exposure to nature predict better health outcomes? 2) To what extent are variations in exposure to different types of urban nature (e.g. trees, understory vegetation) associated with human health? I used Google Street View images and National Land Cover Dataset 2011 to estimate participants’ daily exposure to nature, and two standard questionnaires (e.g. SF-12 and Perceived Stress Scale) to assess health outcomes. Results show that greater exposure to nature in daily life is associated with better health outcomes. Specifically, higher neighborhood concentrations of tree canopy are related to better physical health, overall health and better capacities to control stress. In contrast, the understory vegetation has a negative relationship with stress and mental health. The most important contribution of this dissertation is to clarify the effects of newer types of green infrastructure (e.g., bioswales) on human health through studies using an experiment and a survey. By combining an experimental study in a controlled setting with a survey without any intervention, results of the three empirical studies broadened our knowledge, verified the Attention Restoration Theory and increased our confidence in the findings. A number of policy and design implications can be derived from this dissertation. Planners, designers and administrators should be aware of the intrinsic and supportive roles urban green infrastructure can play in promoting public health. We should develop policies and designs that respond to people’s needs. Policy makers and public health providers should introduce green infrastructure at every door step and offer nature-based subscription for those in needs.
Issue Date:2019-12-06
Rights Information:Copyright 2019 Xiangrong Jiang
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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