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Title:Establishing dose-response curves for the impact of urban forests on recovery from acute stress and landscape preference
Author(s):Jiang, Bin
Director of Research:Sullivan, William C.
Doctoral Committee Chair(s):Sullivan, William C.
Doctoral Committee Member(s):Chang, Chun-Yen; Buchner, David; Deal, Brian M.
Department / Program:Landscape Architecture
Discipline:Landscape Architecture
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):mental stress
stress recovery
Landscape preference
tree cover density
urban forestry
public health
environmental therapy
psychophysiology
landscape planning
Google Earth aerial photography
eye-level panoramic photograph
Abstract:Although it is well established that exposure to urban forests can help reduce stress in individuals, the shape of the dose-response curve is entirely unclear. It is not known if a small amount of nature is enough to induce stress recovery effects, whether increases in the tree cover density produce additional stress recovery effects, or even if the relationship is linear. Lack of this knowledge prevents landscape architects from making science-based design and management decisions that might improve the health and longevity of people in the communities they serve. The central research question of this dissertation is: what is the dose-response curve of the influence of viewing community street videos with a high diversity of tree cover density on stress recovery as measured by physiological or self-reported indicators of stress status? I also examine the dose-response curve of the relationship between tree cover density and landscape preference. In order to provide justification for the methods I use to assess tree cover density for the dose-response curves, I explore the following questions: Among measures of tree cover density from panoramic photographs and Google Earth aerial photographs, which one best represents people’s perceived tree cover density? How do those different measures correlated to each other? This dissertation answers these questions in four separate studies. In the first study, I examine the extent to which four measures of tree cover density were correlated with one another for sites with low, medium, and high levels of tree cover. In the second study, I examine the dose-response curve for tree cover density and preference. The different measures of tree cover density for these two studies are calculated using panoramic and Google Earth photographs and a photograph-survey involving 320 participants. In the third and fourth studies, I examine the dose-response curve of impacts of viewing ten 6-minute, 3-D community street videos with varying levels of tree cover density on stress recovery. 160 participants completed a public speaking and an arithmetic task to induce stress. Then they were assigned to watch a 3-D video as a nature treatment individually. I measured each participant’s stress levels during the experiment. Specifically, in the third study, I measured the participants’ self-reported stress levels to assess the stress recovery effect. In the fourth study, I measured the participants’ salivary cortisol levels and skin conductance levels to assess the stress recovery effect. Finally, I created a summary stress recovery index based on results from these two studies to generate a general dose-response curve. Findings from the first study suggest that, among the three objective measures, percent tree cover calculated from panoramic photographs most reliably represents people’s perceived tree cover density and landscape preference. Further, findings from the second study suggest that the dose-response curve between the tree cover density calculated from panoramic photographs and landscape preference can be best represented by a power trend line, not a straight line. Results from the first two studies justify my use of panoramic photographs to measure tree cover density in the third and fourth studies. Findings from the third study suggest the dose-response curve between the tree cover density and self-reported stress recovery can be explained by a positive, straight line. Findings from the fourth study suggest that for men, the dose-response curve is best explained by an inverse U-shape, quadratic curve. The results for women, however, showed no statistically significant relationship between percent tree cover and stress recovery. Further analysis shows the dose-response relationship between tree cover density and the summary stress recovery index can be best explained by a linear equation. There is a small but significantly positive association between eye-level percent tree cover and all participants’ summary stress reduction. In sum, these results are the first to describe dose-response curves for the impact of varying levels of tree cover density on stress recovery and also landscape preference. These studies are the first to describe the relationships among multiple measures of tree cover density. In addition, these studies make important methodology contributions regarding the use of multiple measures of mental stress and 3-D visual technology. These findings should be of significant interest to practitioners, policymakers, and public health officials.
Issue Date:2014-01-16
URI:http://hdl.handle.net/2142/46889
Rights Information:Copyright 2013 Bin Jiang
Date Available in IDEALS:2014-01-16
2016-01-16
Date Deposited:2013-12


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