The Curious Healing Power of Trees

In 1984, Roger Ulrich (who is now considered the most cited and influential evidence-based healthcare design researcher in the world) noticed a pattern in patients who were recovering from gallbladder surgery: the patients who had rooms that looked out onto a patch of trees close to the hospital were being released from the hospital a day sooner, on average than others who had identical rooms, but whose windows faced a wall.

Do trees help people heal?

That is the question that a study in the journal Scientific Reports seeks to solve. The study, led by University of Chicago psychology professor Marc Berman, compares two large block-by-block data sets from the city of Toronto, Canada; the first data set measures the distribution of green space (as determined by satellite imagery and a comprehensive list of all 530,000 trees planted on public land, and the second data set measures health from detailed surveys of 94,000 respondents. After crunching the numbers, Berman and his group showed that for every ten trees on any given block, the nearby residents felt 1% healthier. Berman mentioned of the results, “To get an equivalent increase with money, you’d have to give each household in that neighborhood ten thousand dollars — or make people seven years younger.”

The most interesting point taken from the data is more subtle. These health benefits come almost entirely from trees planted along streets and in front yards, where people walk past them. Trees in back yards and parks didn’t seems to affect the analysis as much. It could be that trees along roads have a larger impact on air quality, or that avenues with trees encourage people to walk more. But Berman considers another possibility that is much like Ulrich’s window discovery…

Maybe it’s enough just to look at trees.

A decade prior, Berman led a study that sent volunteers on a 50-minute walk through either an arboretum or city streets, then gave them a memory and attention assessments. The volunteers who took the nature walk performed around 20% better than those who didn’t. They were also in a better mood, even if that didn’t affect their scores. “What we’re finding is that you don’t have to like the interaction with nature to get the benefits,” Berman said. Some of these walks took place in June, and others in January; most people didn’t particularly enjoy trudging through the cold Michigan winter, but their scores were just as high as in the summer trials. Volunteers who were somehow distracted or out of focus seemed to gain the biggest benefits. An end-of-workday nature walk packs a greater  punch than a similar walk first thing in the morning, and the boost is five times bigger in people who have been diagnosed with depression.

Ulrich’s work has already “directly impacted the design of many billions of dollars of hospital construction,” according to one health-care trade publication. One possibility may be that we rebuild our cities and move toward more colorful streetscapes and building with more organic patterns that simulate the ones we see in nature. Berman’s goal is a little less artistic: we wants people to plant more trees. The results of his experiment reveal a clear and consistent message. A walk in the woods is better than a picture of a tree, which is better than an abstract image, no matter how soothing. Something within us responds to nature. If someone offers you ten thousand dollars or ten trees, take the trees.

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