Many studies over the years have shown that citydwellers benefit greatly from green spaces in urban areas. Now, the surprising discovery is that too much green space may be as bad as too little. Architects at HKU’s Urban Environments and Human Health Lab (UEHH Lab) have found a way to measure the optimum dose-response relationship between greenness and mental health outcomes. The doseresponse curve can be rationalised by a quadratic function (an inverted-U shape curve). “The determination is based on a systematic analysis of quantitative findings published in the last 40 years,” said research leader Professor Bin Jiang, Associate Professor in the Division of Landscape Architecture and Founding Director of the UEHH Lab. “This is a critical theoretical contribution: the implications have strong potential to influence future urban planning and public health,” he said, adding that the finding could also affect environmental psychology and landscape architecture in three particular areas. “First, it breaks a ‘common sense’ assumption that more greenness is better for mental health,” said Professor Jiang. “In fact, the finding reveals that extremely low and extremely dense greenness have an adverse effect on mental health, and it is a moderate level of greenness which can provide optimal mental health benefits. “In the study, we provide a table to suggest threshold values of greenness that are associated with nonadverse, satisfactory, highly beneficial and optimal effects on mental health. This line of findings can guide the planning and public health professionals to allocate green landscape resources in a more accurate and beneficial way.” Green Screen Moderation is key Second, if adopted by planning authorities, the finding that ‘moderate is best’ could reduce the overuse of public resources to build too many green spaces. “The development of urban environments is a balance of many different land uses and public interests, so a toogreen city might not be necessary, and may even be as bad as too barren a city,” said Professor Jiang. He also suggests that this thinking could change the economic landscape of town planning – if a city is spending money providing too much greenness, it “means the city must sacrifice opportunities to provide land for housing, public services, commercial and business functions and infrastructures,” he explained. “This is especially true for Hong Kong where nature conservation is given great emphasis but at the same time millions of people live in apartments that are crowded and small.” Third, it provides solid evidence to public health department and professionals that contact with nature can produce stable and significant mental health benefits. “It urges the public health department and professionals to regard regular contact with nature in people’s living environments as a solid part of public health policymaking and therapeutic treatment,” said Professor Jiang. The study found specifically that eye-level greenness has a more robust link with people’s mental health response than the top-down greenness, suggesting that town planners pay much more attention to how much greenness can be seen by people in their daily lives rather than just measuring the percentage of a region or city that contains green spaces. The development of urban environments is a balance of many different land uses and public interests, so a too-green city might not be necessary, and may even be as bad as too barren a city. Professor Bin Jiang 40 years of data The researchers reviewed relevant articles published in the last 40 years (1985–2025) and obtained the quantitative data about the curves reported by each study. They then standardised the data and plotted all the curves in a single diagram. They established HKU researchers in the field of landscape architecture and their international collaborators may have found a law that can describe the relationship between doses of nature in the city and mental health responses. a checklist of possible patterns based on recognised theories of environmental psychology and used statistical models to compare the robustness of each curve model. Through these comparisons, they identified that the quadratic function curve is the best way to describe the dose-response relationship for most of the published findings. The article has received much attention from researchers and professionals in multiple fields, including urban planning and design, environmental health, environmental psychology, landscape architecture, and architecture. “We have received overwhelmingly positive feedback,” said Professor Jiang. “These findings fill what has been a critical theoretical and practical gap.” He added: “The study is an outcome of an interdisciplinary cooperation with Dr Jiali Li, Professor Peng Gong, Professor Gunter Schumann, Dr Xueming Liu and Dr Pongsakorn Suppakittpaisarn and their contributions ensure this study has the potential to influence multiple fields, including urban geography, environmental psychology, landscape architecture, and urban planning.” The UEHH Lab is now continuing this line of research, working on another paper on the dose of duration (how long each time on average), frequency (how often), and accessibility (how many minutes’ walk) to green space exposure, and the effect of these factors on mental health. When the new study is complete, they plan to combine both sets of findings to construct a holistic guideline for a healthy lifestyle related to contact with nature in daily life. HKU Bulletin | Nov 2025 Research 26 27
RkJQdWJsaXNoZXIy ODI4MTQ=