How Trees Calm Us Down

In 1984, a researcher named Roger
Ulrich noticed a curious pattern among patients who were recovering from
gallbladder surgery at a suburban hospital in Pennsylvania. Those who
had been given rooms overlooking a small stand of deciduous trees were
being discharged almost a day sooner, on average, than those in
otherwise identical rooms whose windows faced a wall. The results seemed
at once obvious—of course a leafy tableau is more therapeutic than a
drab brick wall—and puzzling. Whatever curative property the trees
possessed, how were they casting it through a pane of glass?

That is the riddle that underlies a new study in the journal Scientific Reports
by a team of researchers in the United States, Canada, and Australia,
led by the University of Chicago psychology professor Marc Berman. The
study compares two large data sets from the city of Toronto, both
gathered on a block-by-block level; the first measures the distribution
of green space, as determined from satellite imagery and a comprehensive
list of all five hundred and thirty thousand trees planted on public
land, and the second measures health, as assessed by a detailed survey
of ninety-four thousand respondents. After controlling for income,
education, and age, Berman and his colleagues showed that an additional
ten trees on a given block corresponded to a one-per-cent increase in
how healthy nearby residents felt. “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,” Berman told me.