Scientists Tested 8 Global Cities for Tree Cover Using ‘3-30-300’ Rule- Only One Came Close To Their Standards

Turns out, there's a standard to measure major cities of the world in terms of how green they are. Using the simple ‘3+30+300 rule’ to answer three questions that collect data on the greenery of a cityscape, scientists have set a minimum criterion required to be implemented in big cities across the world to ensure nature preservation in an urban environment. Eight global cities– Melbourne, Sydney, New York, Denver, Seattle, Buenos Aires, Amsterdam, and Singapore were tested based on the rule. These cities are regarded as leaders in urban forestry and green space development. However, the results were not as reassuring besides only one city drifting closer to the basic standards, per a report by The Conversation. 

Can you see three trees from your home, school, or workplace? This was the first question that needed to be addressed to qualify for the test. Is there tree canopy cover shading at least 30%? Can you spot a park within 300 meters of the building? The answers to these three questions accounted for the city’s qualification as a healthy, green, and heat-tolerant cityscape with the potential to tackle climate change. Most of the cities failed to meet the standards of the 3+30+300 rule. The main challenge was adequate canopy coverage in even the most affluent cities like New York and Sydney. Though many cities qualified in the first factor, that is, to spot three trees from their location, the canopy coverage, essential for cooling cities, was sparse and appears to be a negative indication of heat tolerance. 

Sourcing information from publicly available data by OpenTrees.org and from local governments, the researchers picked cities from every continent. Melbourne is known for its Urban Forest Strategy and New York has successfully implemented projects like MillionTreesNYC and The Highline. The tropical greenery of Singapore is credited to parks like Gardens by the Bay and Bishan-Ang Mo Kio Park. Meeting the three trees requirement did not seem to be an issue for most cities, however, significantly lagged behind in canopy cover. In Melbourne, 44% of buildings had views of three trees but only 3% had adequate canopy cover. Sydney had 84% of tree views but only 17% of buildings enjoyed shades from trees. Whereas, Seattle fared well with 45% of canopy coverage. 

Singapore topped the list with 75% canopy coverage, 60% views of three trees, and 80% of buildings had parks within a 300-meter radius– a clear winner. Amsterdam also scored better on parks while NYC and Buenos Aires had a poor score on the criteria. The rule originated in Europe and eventually spread to big cities around the world, thanks to Dutch urban forestry expert, Professor Cecil Konijnendijk. He introduced the "3+30+300" rule after reviewing the evidence linking urban nature to human health and well-being, in 2022. The report explained that humans are likely to suffer from depression, anxiety, obesity, and heatstroke in cities with limited green infrastructure. 

Cities including, Haarlem in the Netherlands, Malmo in Sweden, Saanich in Canada, and Zurich in Switzerland have incorporated strategies to execute urban forestry plans. Analyzing the test results, researchers were baffled by the odd ratio of buildings having tree views but poor canopy coverage. Hence, they concluded that the issue was in the size of trees that failed to create enough shade, mostly due to urban factors. In addition to scarce planting density, cities need bigger, healthier, and longer-lived trees planted closer to increase the canopy coverage affecting the cooling factor.