How trees can help cities tackle depression – and climate change – in Latin America
October 10, 2021
By: Claire Slesinski, MSPH
Senior Program Manager for Global Urban Health
Are urban environments in Latin America “depressogenic”?
It could be said that Latin American cities have been (unintentionally) designed to make people depressed.
The populations of Latin American cities experience extreme inequality; rapid and unplanned urbanization resulting in long commutes on informal transportation; exposure to high levels of air pollution; high rates of violence, crime, and homicide (Latin America as a region experiences the highest levels of violence in the world); high levels of poverty and high proportions of the population (more than 20%) living in slums or informal housing. All these factors are known or believed to cause an increase in the risk of depression.
With nearly 530 million people, more than 80% of the region’s population, living in “depressogenic” environments, mental health should be integrated into urban planning and policy discussions. Depression is the most common mental illness in the world, and this is also true in Latin America where an estimated 5% of the adult population, or approximately 26.5 million people living in Latin American cities, suffer from the disease. Despite how common this mental health challenge may be in the region, 6 in 10 people who experience depression in Latin America do not receive any treatment due to both social stigma and a lack of access to care. Additionally, those in the region who are living in poverty or with fewer resources are athigher risk of depression.
Moreover, the ongoing COVID-19 pandemic and escalating climate crisis will continue to put pressure on the mental health of populations throughout the region, creating an increasingly urgent need to provide relief and mental health care.
Trees as an intervention for depression
What can urban health researchers, urban planners, and urban policymakers do in the face of such a complex issue? Though it will not solve all the problems that Latin American cities face, simply planting trees may play a part in improving mental health, alleviating some of the impacts of climate change, and improving overall physical health and wellbeing of urban populations.
Two studies conducted in Leipzig, Germany and London found that the presence of trees in urban settings is associated with lower rates of anti-depressant prescriptions. The study conducted in Germany also found that the effect of trees was especially high among those with lower socioeconomic status. Another study, a cluster-randomized trial in Philadelphia, USA found that people living in neighborhoods where vacant lots were cleaned up and filled with greenery – grass and some trees – experienced a 41.5% reduction in self-reported depression symptoms. Importantly, the impact of this study was even stronger among those living in neighborhoods below the poverty line – this group experienced a 68.7% reduction in self-reported depression symptoms. These findings are line with other research which has found that the presence of urban trees and exposure to urban forests are linked with better mental health and reduced risk of depression.
A recent review of the health impacts of urban trees found that the available evidence suggests that urban trees reduce the negative impact of urban features that may worsen mental health. According to the review, urban trees reduce air pollution, reduce the risk of heat-related illness and death during periods of excessive heat, and may contribute to a reduction in violent crime.
Trees support climate change mitigation and adaptation
Beyond the mental health benefits of trees, more vegetation in cities can play a small part in combatting climate change.
Trees help to lessen the impact of the heat island effect on human health. Trees and other vegetation extend their roots into the soil of slopes, hills, and mountainsides in and around cities, thereby stabilizing the soil and making mudslides and landslides less likely. Mangroves in or near tropical and subtropical coastal cities can help to prevent flooding and capture greenhouse gases, while providing a habitat for local wildlife and producing health benefits for those who visit parks and areas where mangroves are present. In fact, urban trees of all kinds can play a role in capturing carbon dioxide and slowing climate change.
In short, “street trees and the urban forest are more than luxurious afterthoughts,” providing a wide range of benefits to human health and wellbeing, including but not limited to a reduced risk of depression.
What are Latin American cities doing to increase the presence of urban trees and forests?
A regional movement is growing to increase the number of trees in cities. Here are two examples of initiatives in Colombia and Argentina that have or will greatly increase the number of trees in large urban centers.
Corredores Verdes, Medellin, Colombia
An ecological initiative in Medellin, Colombia, continues to be an impactful example of how cities can increase vegetation and trees throughout cities. The city’s “Corredores Verdes,” (green corridors) are an interconnected network of greenery, vegetation, and trees that that span across the city, many of which have bicycle and walking paths incorporated into them, allowing for active transportation through green pathways throughout the city. Since 2016, citizens hired by the government to become urban gardeners have planted 8,800 trees and palms along 30 corridors that cover 65 hectares. Along one busy street, gardeners planted nearly 600 trees and palms as well as 90,000 other plants. After three years of the program, Medellin’s heat island effect was reduced by 2o Celsius (3.6 o Fahrenheit), and the city expects a further decrease of 4-5°C by 2050, reversing previous increases in city temperatures.
It should be noted, however, that low-income community members and some researchers say that “as the Municipality of Medellín is containing and beautifying low-income neighborhoods through grabbing part of their territories and turning them into green landscapes of privilege and pleasure, communities are becoming dispossessed of their greatest assets—location, land and social capital.”
Nearly 9,000 trees and palms have been planted along 30 corridors in Medellin, Colombia.
Highway to be converted into elevated public park in Buenos Aires, Argentina
The city of Buenos Aires, Argentina is working to convert a highway that cuts through the city into an elevated public park. The highway passes through Barrio 31, one of the oldest informal settlements in the city, whose residents experience extreme marginalization and exclusion from the benefits of living in this large and vibrant metropolis. When still in use, the highway generated noise and air pollution that spilled over and across Barrio 31, affecting its residents.
This change will increase the amount of public space per Barrio 31 resident by 387%. The park will incorporate green areas and connect the neighborhood with the rest of the city through walking and biking paths as well as electric public transport. The removal of cars from the highway will drastically reduce the amount of air and noise pollution in Barrio 31. Planners also estimate that over 6,000 tons of CO2 will be absorbed every year by the 4,000 trees that will be planted in the park.
Despite the prospect of increases in public space and greenery, community members have said that the city has not adequately included them in discussions and decision-making processes. A community leader that has worked in the neighborhood for decades says that “the process of constructing new housing did not specifically involve the population, and because of this, policies were not decided on by residents, but by the government.” Residents fear displacement, economic hardship, and gentrification due to the ongoing changes in their neighborhood, including the installation of this elevated park.
The Ilia highway, which cuts through Barrio 31, will be converted into an elevated park where 4,000 trees will be planted.
A growing regional movement to plant more trees in cities, with increasing worries of exacerbating inequities
Some good news: most Latin American cities have been in the process of “re-greening” at least since the year 2000. A recent paper accepted to Environmental Research Letters reports that 82% of cities included in the SALURBAL study experienced increases in greenness between 2000-2015.
There are many other signs of continued political will and momentum to support the increased greening of Latin American cities and expand urban forests in the region. In 2014, the Development Bank of Latin America (CAF) launched a forests program for the region which included the “recovery of urban forests and restoration of green spaces.” The Inter-American Development Bank is exploring the best way to support “nature-based solutions” to generate climate change resilience in the region. Interest in urban forestry research is increasing over time, and Latin American countries such as Brazil have begun to invest in the restoration of urban tree cover and urban forests.
This momentum will have positive impacts on the mental health of Latin American urban populations for many generations to come. However, cities must work closely with marginalized communities when implementing greening initiatives to avoid exacerbating inequities through displacement and gentrification. To ensure that the benefits of trees and green space are equally accessible to all, governments and development funders must make a concerted effort to engage with the most vulnerable populations in Latin American cities and give them real decision-making power.
If this can be achieved, the benefits of trees, plants, and green space can truly benefit the mental health of urban populations equitably, and potentially help to reduce existing inequities in depression across the region.