The shade of a single tree can provide welcome relief from the hot summer sun. But when that single tree is part of a small forest, it creates a profound cooling effect. According to a study published today in the Proceedings of the National Academy of Sciences, trees play a big role in keeping our towns and cities cool.

According to the study, the right amount of tree cover can lower summer daytime temperatures by as much as 10 degrees Fahrenheit. And the effect is quite noticeable from neighborhood to neighborhood, even down to the scale of a single city block.

“We knew that cities are warmer than the surrounding countryside, but we found that temperatures vary just as much within cities. Keeping temperatures more comfortable on hot summer days can make a big difference for those of us who live and work there,” says Monica Turner, a University of Wisconsin–Madison professor in the department of Integrative Biology and a co-author of the study.