Urban tree layout influences human health and mortality rates

Trees and parks not only add open, pleasant spaces to cities but also boost human health in multiple ways, from filtering air pollution to providing shade and cooling down hot urban areas. 

Many governments worldwide have announced bold plans to plant more trees over the coming years, partly due to climate change and rising temperatures. However, in heavily built-up cities, finding room for additional green spaces remains a pressing challenge. 

The question becomes: How can municipalities best arrange trees in existing green zones to achieve maximum benefit?

That question has drawn the attention of researchers and city planners alike, who must factor in specific local conditions such as geography and climate. 

Linking trees and human health

Investigators at ETH Zurich have turned their focus to this issue not just within Switzerland, but also across Asia. 

Through the work of a team from the Future Cities Lab, a program run in Singapore by ETH Zurich and the National University of Singapore (NUS), researchers uncovered surprising connections between the way cities manage their trees and the general health status of residents.

The researchers’ first step involved analyzing high-resolution data on tree canopy coverage within a 500-meter radius of each person’s home. 

Beyond calculating the total area of tree clusters, they assessed how near these clusters were to each other, how they connected, how complex their shapes were, and how fragmented they appeared.

They then linked these details to survival data – specifically, the time to natural-cause deaths (due to age or disease) – for more than six million adults. 

The records were provided by the Swiss Federal Statistical Office, which covered a decade from 2010 to 2019. To maintain privacy, the Federal Statistical Office had rounded each individual’s home coordinates to the nearest 50 meters.

Tree canopy cover and mortality rates 

Through careful data analysis, the researchers discovered that the extent of a neighborhood’s tree canopy and its layout were associated with mortality rates. 

The study showed a significantly lower risk of death among residents living in areas with larger, more cohesive, and better-connected tree coverage, compared to those where the coverage was more fragmented or exhibited complex shapes. 

This link was particularly clear in densely populated peri-urban or urban zones marked by poor air quality and high temperatures. In such environments, efficiently structured forested spaces might deliver stronger health advantages than in more dispersed contexts.

Even though the findings offer an insightful initial glimpse, the researchers maintain that it is premature to pinpoint specific causes. They cannot yet say with certainty how tree canopy configuration positively affects people’s well-being. 

Still, at the individual level, their outcomes broadly align with similar studies performed at the community level in Philadelphia, Tehran, and Taipei.

Connecting isolated green spaces

Dengkai Chi is a postdoctoral researcher at the ETH Future Cities Lab and the study’s first author.

“Although we can’t yet define a direct causal link, when we have addressed factors such as age, gender and socio-economic status, the data shows clear correlations. Our results provide plausible indications that human health may be influenced not only by the quantity of trees but also by their spatial distribution,” said Chi.

These results demonstrate the value of considering carefully how trees are arranged. By deliberately planning a city’s green areas, officials can possibly extract greater health benefits for residents. 

“In order to fully exploit trees’ potential to support human health, cities should strive to not only increase the number of trees but also to connect isolated green spaces – including by creating tree-lined boulevards,” Chi said.

Interestingly, the study indicates that simpler, more compact patches of tree canopy – for instance, circular or rectangular shapes – might have a more beneficial health effect compared to complex, scattered forms. 

One plausible reason is that simpler geometries yield bigger central zones, encourage ecological diversity, and possibly spur people to visit these green spaces more frequently.

Standards for urban greening initiatives 

Despite these early observations, the researchers acknowledge that significant work remains. “We’re still at the very outset of this research,” Chi said.

Multiple important factors could not be included in the study, such as pre-existing illnesses, smoking status, or whether individuals actually use local parks. Furthermore, the results apply to neighborhood scales and might not hold uniformly for an entire city.

Initial clues suggest that across a broader city, the effect on health might correlate with how fairly green spaces are distributed, ensuring that a large share of the population can reach them easily. 

The team hopes to explore these aspects in further research, aiming to clarify the relationships between green space organization and health.

Chi points out that in developing policy suggestions for officials and planners, the research team will need to produce more quantitative assessments and identify precise thresholds. Such work could help define actionable standards for urban greening initiatives.

Overall, the study provides further confirmation that green infrastructure does not solely beautify urban settings but may also be tied to tangible health benefits. 

As climate change urges administrators to plant more trees and as cities become increasingly crowded, focusing on the strategic placement and design of tree canopies may become just as critical as planting them in the first place.

The study is published in the journal Lancet Planetary Health.

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