Canadian city-dwellers surrounded by a symphony of birds and a variety of trees might be reaping surprising benefits: better mental health.
A Canadian study, published in Nature last month, found that living in a city neighbourhood rich with bird diversity and tree species was linked to increased reporting of good mental health.
The study found that people living in areas with a greater variety of birds reported feeling happier by 6.64 per cent. Similarly, those living near a wider range of tree species reported 5.36 per cent higher rates of good mental health.
These increases were seen even when considering other factors like socioeconomic status.
“We found that there was a positive association between mental health and the diversity of trees and the diversity of birds in people’s postcodes,” explained Rachel Buxton, the study’s lead author and assistant professor at the Institute of Environmental Science at Carleton University.
“There is a whole wealth of other research that shows taking a walk in nature is super good for your mental health and your physical health. So ours is just one piece of this literature and the story that’s saying, ‘It’s great medicine for your mental and physical health to go outside and be in nature’,” she told Global News.
In any given year, one in five Canadians experiences a mental illness, according to the Centre for Addiction and Mental Health (CAMH).
As the population continues to age and urbanize, it is estimated that within a generation, 8.9 million Canadians will be living with a mental illness, the Mental Health Commission of Canada reports.
While research has shown that neighbourhood characteristics and geographic inequalities (such as unemployment, schools, and low income) predominantly explain mental health outcomes, especially in urban environments, the researchers also found that other factors, such as green space, can significantly impact mental health.
To explore the link between bird and tree diversity and mental health, the researchers analyzed data from the Canadian Community Health Survey (2007 to 2022) alongside information on bird and tree species diversity using eBird, a crowdsourced app and a national forestry inventory. They then looked at this data across numerous Canadian cities, like Vancouver, Calgary, Toronto and Montreal.
The researchers specifically focused on birds and trees because they represent a form of “passive exposure” to nature, Buxton explained. In other words, you can experience these aspects of nature simply by being outside, like hanging out on your deck or walking to the bus stop.
The study found a strong positive correlation between the diversity of birds and trees in a neighbourhood and self-reported mental health.
“And it’s interesting because there are so many things that influence mental health, such as your income, education or marital status,” Buxton said.
“But we still found this positive association between the diversity of trees, diversity of birds and people’s self-reported mental health. And it had around the same effect as eating fruits and vegetables.”
Why chirpy neighbourhoods might make you happier
The Canadian study is not the first to find a link between nature and improved mental well-being.
A 2015 United Kingdom study, published in the International Journal of Health Geographics found that higher bird species richness was associated with the prevalence of good health. And a 2021 German study published in Landscape and Urban Planning found that plant and bird species richness are positively related to mental health.
Buxton suggested the link between bird and tree diversity and mental health might have roots in our evolutionary past.
“Humans evolved in natural environments, and we evolved in taking our cues from natural environments,” she said.
“So in an environment where there are lots of different species, so lots of different birds and trees, that’s a pretty good indicator that that environment can meet all of our needs. There’s more to eat, there’s more trees for shelter, probably more water because that’s going to feed the trees and, and the birds.”
In an environment rich with bird species and trees, our brain enters what Buxton called a “rest and digest” mode, allowing for mental recuperation and restoration from various stressors.
“In an environment with fewer species, not as many birds, not as many trees, maybe our needs can’t be met, we have to go out and look a bit further for something. We have to survey our surroundings and that starts to kick in our fight-or-flight response.. and that stress response kicks in,” she added.
While the number of street and park trees is estimated to be increasing in Canadian municipalities, the researchers argue that the amount of natural forest cover is decreasing, and climate change, diseases and pests are predicted to increase urban tree mortality.
Although biodiversity loss is occurring in Canadian cities, Buxton said there are still great initiatives underway, such as tree planting, pollination projects and community gardens, to help natural environments thrive.
“Given the association between tree and bird diversity and self-rated mental health at the urban neighborhood level in Canada, holistic nature-based interventions that bolster biodiversity can be seen as a key tool for public health planning and policy in Canadian municipalities,” the study concluded.