Taking a walk in a wooded park seems to make people feel better. Psychologist Omid Kardan and his colleagues at the University of Chicago note in Scientific Reports that the subjective experience of a mood boost from a nature walk is a real phenomenon.

Researchers accessed health records of more than 30,000 Toronto residents and evaluated self-perceptions of health and prevalence of physical and mental health problems, as well as other details.

On average, the more trees in a city block, the better a person’s perception of health.

Other studies have found that health perception correlates with objective measures of health.

The study did not determine how trees might boost health, but one explanation is that greenery improves urban air quality by drawing air pollutants out of the air.

Spending time near trees may also offer a psychological benefit by lowering stress, which can boost physical and mental well-being.