Recent research shows that city trees can help reduce depression. Photo courtesy of Kimberley Zak (@KimZakPhoto on Instagram)

There are many reasons to love trees, whether in faraway forests or in our own backyards. Even in cities, trees provide a myriad of public health benefits, including mitigating climate change, extreme heat, air pollution, and mental health issues–wait, mental health? 

Surprisingly, trees can help with managing ADHD symptoms and reducing stress. Now, recent research published in renowned science journal Nature reveals that city trees can also decrease depression.

Researchers in Leipzig, Germany mapped individual city trees with health data from 9,751 adults to examine the relationship between trees and mental health. Researchers assessed the minimum “dose” of trees needed to yield a positive mental health result by looking at the number and type of trees present at varying distances from the home. 

The study found that living in a home with trees nearby reduces the risk of depression. Researchers found that the more trees within a 100 meter radius from a home, the fewer cases of clinical depression. Importantly, though this trend held across income levels, it was most significant in low-income households. 

While ecologists often place a premium on biodiversity, researchers found that tree diversity didn’t have an effect on depression. Even at close range, more variety in tree species didn’t affect the relationship between trees and depression. Researchers The authors speculate that because most non-ecologists cannot distinguish between tree species, having more trees rather than a variety of different trees is more important for mental health.

Distance, though, matters for the positive effect of trees. Beyond 300 meters from the home, trees had little impact on antidepressant prescriptions. For everyone to benefit from trees, they  need to be evenly distributed throughout neighborhoods, not only concentrated in a single green space.

Planting trees along streets, close to people’s homes, will have the greatest positive effects for low-income families. City planning and tree planting that facilitates this incidental contact with trees can create a lot of good for a lot of people, without a lot of effort. 

Though this study paints planting trees as a simple solution for addressing both mental health and environmental concerns, there are limitations to consider. 

Planting trees isn’t just about mental health–it’s a matter of environmental justice as well. In order to meaningfully apply the results of this study to the US, we need to take into account race and equity.

In Leipzig, researchers did not find evidence of a relationship between income level and tree cover, but the reality for American cities is that wealthier neighborhoods almost always have more trees. Urban forestry initiatives must endeavor to remedy this disparity, taking care to avoid green gentrification in the process. 

Given that Leipzig is an overwhelmingly white European city, it’s not surprising that the authors weren’t able to consider race as a factor in their study. In the US, however, race is the single most important factor in predicting exposure to environmental hazards, regardless of socioeconomic status. 

Even so, the study is a useful starting point for how street trees can be used to improve well-being for everyone. There is now research to support that if we, in our communities, want to take the mental health and environmental crises seriously, then street trees can and should be an integral part of urban infrastructure.

Achieving the most important effects of street trees doesn’t have to be difficult or costly. We just have to keep equity in mind. Indeed, as one researcher remarked, the study is really good news for mental health justice:  “You don’t even need large-scale expensive parks: more trees along the streets will do the trick. And that’s a relatively inexpensive measure.” Being happier might be as simple as planting more trees.