Longer life expectancy, fewer mental health issues, and improved cognitive functioning are just a few of the many well-known health advantages of urban green space. The amount of green space required, however, to improve people’s health is still up for debate.
The 3-30-300 green space rule and better mental health have been compared in a recent study led by Barcelona Institute for Global Health.
Everyone should, by this rule of thumb, be able to see three or more trees from their home, have 30% of their neighbourhood covered in trees, and not live more than 300 meters from the closest park or green space. Cecil Konijnendijk, an urban forester, first proposed the rule, and numerous other forestry professionals, as well as urban planners have actively supported it.
Fewer Trees Means More Therapists?
Full compliance with the 3-300-300 green space rule was linked to better mental health, less medication use, and fewer trips to the psychologist, but only the last link was statistically significant. But neither being able to see trees from windows nor having access to a large green space was linked to better mental health in a significant way.
According to the findings, only 4.7% of the surveyed population met all three criteria of the green space rule.
A little more than 43% of respondents had at least three trees within 15 meters of their home, 62.1% had a major green space within 300 meters, and 8.7% lived in an area with enough surrounding greenness. However, nearly 22.4% possessed none of these characteristics.
Not Much Green Space In Barcelona
This cross-sectional study was based on a sample of 3,145 Barcelona residents aged 15 to 97 years who participated in The Barcelona Public Health Agency’s 2016 Barcelona Health Survey and were recruited at random. The 12-item General Health Questionnaire was used to assess mental health status (GHQ-12).
Eighteen percent of participants said they had poor mental health, and 8.3% said they had seen a psychologist in the previous year. Furthermore, 9.4% had used tranquilizers or sedatives in the previous two days, and 8.1% had used antidepressants.
“The study found that there is relatively little green space in Barcelona and that the 3-30-300 rule is satisfied only for a small percentage of people, despite its beneficial mental health effects,”
explained lead author Mark Nieuwenhuijsen, Director of the Urban Planning, Environment and Health Initiative at ISGlobal.
“There is an urgent need to provide citizens with more green space. We may need to tear out asphalt and plant more trees, which would not only improve health, but also reduce heat island effects and contribute to carbon capture. Any initiative that leads to a greener city will be a step forward, the key message is that we need more and faster greening,”
Similar studies, according to the research team, should be conducted in cities with more tree cover than Barcelona, because a lack of green space, particularly sufficient tree cover, limits the ability to assess the 30% aspect of the 3-30-300 rule.
“The question is to what extent 30% tree canopy cover is feasible, especially in compact cities,”
the researchers concluded.
Reference: Mark J. Nieuwenhuijsen et al, The evaluation of the 3-30-300 green space rule and mental health, Environmental Research, Volume 215, Part 2, December 2022, 114387