It's no secret: trees are an integral part of how we live on this planet. From their well-known and vital role in the oxygen cycle, and their importance to their ecosystems — they are also central to the human food system. But trees also have other, less obviously integral benefits that manifest in our lives. Sure, without trees it would definitely be harder to breathe — but it might also be harder to just relax.

Their aesthetic value in urban areas aside, there are many reasons to love trees planted in cities. For one, trees reduce stress. According to research, spending time among trees and other vegetation reduces stress while easing brain fatigue. Populations living near trees have a lower amount of cortisol, a stress-related hormone, meaning they experience stress less acutely than people who don't live near trees.

Trees and urban green spaces have also been shown to help children with attention deficit disorder. By simply wandering through a green space before testing, children experienced positive cognitive effects that helped them focus on tasks in ways other settings did not. But reduced stress and increased attention span aren't the only ways trees help humans cope.

A study published in 2012, that examined tree canopy in urban settings, found more tree cover led to less crime. Linked more to psycho-social connection than the calming power of the trees, themselves, the effect is still remarkable. Trees in a neighborhood, according to the study, imply it is better cared for than one without them, suggesting to criminals there will be more police, or more watchful neighbors. Less crime means, tangentially, less stress.

Along with all of these social and psychological benefits, trees serve several practical roles in the urban environment as well, keeping buildings cooler and reducing airborne dust. Not to mention the fact that they are much nicer to look at than a grey, concrete cityscape. They change with the seasons, dehumidifying and cooling cities, while giving us an ever-revolving kaleidoscope of colors and keeping us at least marginally in tune with earth's cycles.

So while trees have started to tune themselves into the urban environment, benefiting from all of those things we might have thought would kill them, more green space means less stress, less heat, more attentive kids, and less crime. Despite their manifold impact, trees might not be the solution to all of civilization's problems; but they might just keep us a little more relaxed while we go about our business. That, as a start, can't be bad.