A new study suggests that you should probably count the number of trees on the block, the next time you are hunting for a house or apartment.
The study found that living on a street with 10 more trees than average (both on the street and in people’s yards) makes you feel as healthy as if you were seven years younger—or as if you were making an extra $10,000 a year.
Researchers already knew that living around green spaces makes people happier, safer, and that greenery can help reduce diseases like asthma by sucking up pollution. But the new study goes deeper to examine the benefits tree by tree.
“We felt that there is a need to quantify the relationship between individual trees
and health in a way that the size of this association can be assessed and compared with other well-known factors such as income and age,” says Omid Kardan, a doctoral student at the University of Chicago and lead author of the study. “This way, planners will have a better sense of this relationship and hopefully consider this factor more seriously in their urban development and public health policies.”
The researchers combed through maps of 530,000 trees on streets in Toronto, and combined that with satellite images of trees in people’s backyards. Then they compared the number of trees to the health of people on each block. Because Canada has universal healthcare, it was easier to eliminate differences neighbors might receive in treatment. The researchers were also able to control for things like income, age, and education. Trees, it turned out, still made a difference.
The more trees on a block, the less likely people are to be obese or have diabetes or heart disease. They’re also more likely to report feeling healthier. The researchers compared the effect to income; the more money people make, the more likely they are to say they feel healthy. Being around more trees is the health and well-being equivalent to making $10,000 more at your job.
Trees along a city street seem to help more than trees in backyards or parks, and trees that stay green all year long also seem to have more benefit. The bigger the tree, the better. It isn’t clear exactly how the trees help; the study just shows that there’s a link.
“One could guess that reduction of pollution, relieving stress, restoration of directed attention, and promoting more physical exercise could be among the possible ways trees benefit health, based on other research,” says Kardan.
Adding an extra 10 trees to a block might be a simple way for cities to improve health. “Ten more trees in every block is about 4% increase in street tree density in a dissemination area in Toronto, which seems to be logistically feasible,” the study says, and points out that planting trees is cheaper than boosting everyone’s salary by ten grand.