As a child grows and develops, the neurons in their brain are said to branch like trees. Being around this very type of foliage could actually help the process along.
A long-term study among 3,568 students in London, between the ages of 9 and 15, has found those kids who spent more time near woodlands showed improved cognitive performance and mental health in adolescence.
On the other hand, other natural environments, like grasslands or lakes and rivers, didn't appear to have the same impact.
"These findings contribute to our understanding of natural-environment types as an important protective factor for adolescents' cognitive development and mental health and suggest that not every natural-environment type may contribute equally to these health benefits," the authors write.
It's not the first time researchers have found a curious connection between the presence of trees and the human state of mind.
In the United Kingdom, similar studies have found children living in greener city neighborhoods have better spatial working memory.
Why that remains is a mystery. Enriched environments are known to shape the human brain, but it's still unclear why green spaces – and especially trees – seem so impactful to young minds.
Some research actually suggests green spaces are linked to structural changes in the brain, including increased white and gray matter, as well as positive changes in the amygdala, which helps control emotions. These changes could therefore be responsible for some of the cognitive and mental health effects we are seeing.
But it seems like trees can do things that other types of foliage cannot. Similar to the new UK study, other researchers have found only trees, not grass, are linked to improved mental health.
Perhaps it has something to do with the fractal patterns found in tree branches. Even as kids, studies have shown humans have an innate appreciation for these shapes, and that could be part of what is calming our minds and invigorating some pathways in our brains.
Yet, like several studies on this topic that have come before, this new one in London has its limitations. Slightly more than half the participants were part of a family whose parents had a managerial or professional occupation.
A paper published in 2019 argues that while children who grow up surrounded by greenery do score better than their peers on cognitive tests, it doesn't necessarily mean trees are to thank. Socioeconomic factors can also play an influential role in child development, and we might be conflating the two.
"Children raised in greener neighborhoods exhibit better overall cognitive ability," the authors of the 2019 study concluded, "but the association is likely accounted for by family and neighborhood socioeconomic factors."
Greenery could also impact our minds by providing refuge from the heat, the noise of the city, or even pollution. There are just so many factors to consider.
It's still too early to say whether being around trees makes children smarter and whether that exposure lasts a lifetime, but given how increasingly urban our landscapes have become, it's worth figuring out whether we can use trees to make life better for people around the world.
The study was published in Nature Sustainability.