If it could be arranged, what would make you happier? An extra £6,600 annual income? Reducing your age by seven years? How about having 10 more trees growing on your street?

For me, it would have to be the seven years, I’ve been falling asleep in front of the TV and my knees are playing up. But as it turns out, all these benefits are equivalent.

In the first ever study to quantify the effect of trees on health and happiness, a team of researchers from the University of Chicago have concluded that having 10 more trees in a city block improves the health perception of those living beside them in ways comparable to a $10,000 (£6,600) hike in personal income, or being seven years younger.

In addition, they found that having 11 more trees in a block correlates to an improvement in cardio-metabolic health comparable to a $20,000 increase in personal income.

The research, led by psychologist Omid Kardan from the University of Chicago and published in the open access journal Scientific Reports, drew on a vast dataset of 530,000 public, urban trees kept by the city of Toronto, which were categorized by species, location, and diameter.

The data was supplemented by high-resolution satellite imagery of tree coverage in the city and compared with detailed long-term investigations into the general health of 30,000 Toronto residents, covering their health perceptions, cardio-metabolic conditions, mental illnesses and more.

The results demonstrate that people who live in neighbourhoods with a higher density of trees enjoy greater well-being, even after taking into account their income, age and education. In addition, the effect on wellbeing was found to be strongest along roads with trees, rather than those located in parks or residents’ gardens.

The study is considered significant due to its size and scope. It also builds on previous research demonstrating the cognitive and psychological benefits of natural scenery, and goes on to recommend that Toronto plants 10 more trees in every block, an increase in street tree density equivalent to about a 4%, which ‘seems to be logistically feasible’. The report also highlights that a $10,000 increase in personal well-being compares with an annual cost of planting and caring for 10 trees of between £300 and $5,000 a year.

However, the scientists highlight that results are only ‘correlational’, and do not conclusively identify how trees improve health. They speculate that health improvements could be the result of improvements to air quality, or reduced stress resulting from being around greenery, a mental effect that translates into physical benefits. They also conclude that being around trees somehow increases the propensity to exercise.

With these knees I’m not so sure, but whatever the scientific reasoning, planting more trees on streets has to be a good thing.

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