Most people are well-aware that trees help clean air by filtering out pollutants and toxins. There are numerous beneficial environmental effects that are derived from trees. Recently, researchers have been investigating whether trees are capable of improving the mental health of humans. According to new research, the number of trees in your neighborhood may have some influence over your mental health.
More specifically, the density of trees in your neighborhood could determine whether you decide to take an antidepressant medication to treat your depression. It has long been known that individuals living in urban environments are at greater risk of developing mental illness compared to those in the country. While there are numerous elements that differentiate the city from the country, one important naturalistic element of the country that provides benefit to city-dwellers is that of “green space,” specifically trees.
Street Trees May Decrease Need for Antidepressants
Newer evidence has attempted to investigate whether trees, plants, parks, etc. (“green space”) are capable of improving mental health. Awhile back, it was discovered that plants at work are able to improve well-being and productivity of employees in the workplace. To further investigate the power of nature on mental health, London researchers took to calculating tree densities in urban environments and comparing these densities with the number of antidepressant prescriptions.
London UK: Landscape and Urban Planning (2015)
Researchers from London conducted this study from which the results have been published in the Journal of Landscape and Urban Planning. As a preface, it should be mentioned that London was an ideal city for conducting this study due to the fact that all citizens receive free healthcare as paid for by the government. This allows anyone to get a prescription for an antidepressant without having to worry about costs (as would occur in the United States).
The Study: Researchers set up the study by first collecting data of the number of antidepressants prescribed in London between 2009 and 2010. They then examined the area in which the antidepressants were prescribed and determined the density of street trees. It should be noted that they only accounted for street trees – not other forms of greenery. They adjusted for various confounds by collecting other data including: age, smoking, socioeconomic status, and unemployment.
Results: Throughout the boroughs of London, there were an average of 40 trees per kilometer. Antidepressant prescriptions ranged from 358/1000 citizens to 578/1000 citizens. They discovered that areas with the greatest density of trees had the lowest rates of antidepressant prescriptions. Researchers went as far as to discover that each additional tree per kilometer resulted in approximately 1.38 less antidepressant prescriptions. This link held up even when confounds like socioeconomic status were taken into account.
Note: The confounds that researchers took into account included: age, whether someone smoked, socioeconomic status, and unemployment. It appeared that the number of trees reduced a person’s likelihood of being on an antidepressant regardless of these factors. While there are other confounds that may have been beneficial to consider, these are some of the better ones to analyze.
Potential benefits of a high street-tree density in urban communities
Based on results of this study, it would appear as though there could be significant benefit derived from living on a street with a high tree density. Additionally projects to increase tree density in low-density areas may be beneficial for mental health of citizens. All future urban planning may want to carefully consider optimizing density of trees in urban environments to potentially improve mental well-being of citizens.
- Calming effect: Elements of nature such as trees tend to have a calming effect in some individuals. Simply going for a walk in the woods or being out in nature is highly therapeutic in that it provides people with fresh air and a reminder that there is more to life than the fast-paced lifestyles lived in urban communities.
- Cleaner air: We already know that big cities tend to have a lot of air pollution from factories and waste processing. Some would argue that having clean air is necessary for optimizing mental function and brain performance. By increasing tree density, it helps clean up some of the pollution, which may offer protection against environmental neurotoxins or other forms of air pollutants. Although this is just one theory, having clean air tends to have a positive physiological effect.
- Coping mechanism: For some individuals, having trees nearby may help them cope with depression without the need for medication. Trees can make the air smell better, they are full of life, and they bring elements of nature to urban environments. This may make people feel more connected with nature and less like they are in a concrete jungle – further helping them cope with a bad mood or stressors.
- Depression reduction: Some would argue that living near more trees reduces your risk of developing depression. While the mechanism behind which trees may prevent a person from becoming depressed is unknown, they may have a positive effect on our mood. If anything they at least clean up the oxygen; toxic air may be detrimental to our mental health and functioning.
- Lack of nature: Places that lack nature or naturalistic elements like trees may make us feel less human and more depressed. Humans evolved being connected with wildlife and other elements of nature. Although it is unknown how a “nature deficiency” may contribute to making us feel depressed or anxious, some suggest that there are clear links.
- Reduce antidepressant usage: Assuming that trees have a positive impact on mental health and functioning, they may be able to reduce the number of antidepressant prescriptions. Although antidepressants can offer benefit to some individuals, many people find them unhelpful and that they create more psychiatric problems than they fix in the long-term. By reducing the number of antidepressant prescriptions, it would save many people from subjecting themselves to a treatment that may not work and/or may cause a chemical imbalance over the long-term.
- Reminder of life: Trees are living organisms that may help some people directly cope with how they are feeling. The energy of a tree is different from that of a post or a building in that it is living, it is changing, and is a reminder of life. Although not everyone has this perspective of trees, the reality is that most people would prefer a tree to a slab of concrete.
- Urban planning: As was already mentioned, street trees may be a beneficial asset that effectively protects against detrimental mental health conditions like depression. Therefore urban planners may want to consider increasing tree density to effectively protect the mental health of citizens. Additionally cities may want to incorporate designs and assign funding to specifically increase the number of public planting programs.
Critical Thinking: Other Factors to Consider
When considering the results of the study, it is important to avoid assuming that correlation equals causation. There are a variety of other components that need to be considered before we can assume that it is the density of trees that are significantly responsible for reducing need for antidepressants.
- True for all types of prescriptions? It would also be interesting for researchers to investigate whether results hold true for other psychotropic prescriptions such as anxiolytics and antipsychotics. Although antidepressants are most commonly prescribed, it would be interesting to understand whether other psychotropic prescription rates are also reduced in areas with greater tree densities. It would even be nice to get data on whether trees reduce need for all forms of medical prescriptions.
- Optimal street-tree density? Researchers may also want to investigate whether there is an “optimal” density of street trees. Although this study has found that more street trees equals reduced number of antidepressant prescriptions, it didn’t investigate whether there is an optimal “density.” Some would speculate that there may be no additional mental health benefit after a specific density is achieved.
- Does the specific type of tree matter? Some would speculate that certain types of larger trees may offer more benefit than smaller ones. Therefore determining whether a specific type of tree and/or the overall mass of a particular tree offers superior benefit compared to one of less mass could be beneficial. If a particular type of tree offers more benefit or double the benefit of another in regards to mental health, money can be saved by planting that particular type and avoiding other types.
- Does having variety in trees matter? This may be too in-depth to study, but it would be interesting to know whether a variety of different types of trees matters more than having a particular neighborhood laced with the same type of tree. Variety in the “green space” could also be examined such as whether the neighborhood with trees, a park, and plants (or gardens) may be superior to a neighborhood of just trees. It is also wondered whether tree height may have an impact on mental health.
- Does the specific country matter? One would speculate that this would hold true in other large countries with equal-opportunity access to government healthcare. It would be interesting to get a better understanding of whether these findings remain true regardless of the city and/or culture. For example, analyze a different urban environment or even a different city in the UK.
- What about suburban and rural communities? In this study, researchers examined street tree density in London for the purpose of improving urban planning. They now will know that the greater the number of trees they plan in a particular neighborhood, the less likely it may be that residents need antidepressants. That said, it would be nice to take a look at suburban planning and even rural planning and attempt to distinguish whether certain features of a particular landscape have an influence on mental health.
- Other confounds: It is unknown as to how well other potential confounds may have been taken into account. Examining other aspects of the city including average size of apartments or homes, whether there is other greenery, air quality, water supply, cleanliness of neighborhood, average level of noise, number of animals (wild or pets), and crime rates could all be investigated. Although the research did examine some confounds, it didn’t examine all confounds and may have missed some potentially important ones in regards to this research.
- Attraction: Streets with more trees may attract people with better mental health and functioning as opposed to those who are depressed or have other psychiatric conditions. This is a potential confound that may warrant investigation.
- Crime: Some research has gone as far as to suggest increasing trees is capable of preventing crime; the greater the density of trees – the lower the amount of crime.
Pleasantness: It could be argued that streets with more trees are inherently more pleasant than communities with less trees.
- Physical activity: Some have suggested that trees may encourage physical activity. While it is unknown how they may encourage physical activity, some believe this to be true.
Conclusion: Further Research is Warranted in Urban Planning / Green Space
While there appear to be some major benefits associated with trees, further studies are necessary to confirm this new finding. In spite of the fact that mounting evidence supports the idea that all forms of “green space” (including trees) is beneficial for human psychological health, the mechanisms by which mental health may improve is unknown. By conducting additional studies, researchers will get a better understanding of potential confounds and possibly better understand the mechanisms responsible for improved psychological health.
Although correlation doesn’t always equal causation, it is important to avoid dismissing the possibility that it could. The findings in this study aren’t “fluke” in that the study was conducted with no scientific basis. Additionally, the researchers did adjust for some relatively major confounds such as socioeconomic status. The bottom line is that the next time you move within an urban community, you may want to choose a neighborhood with more trees than less for the sake of your mental health.
Even if the trees aren’t really doing anything to improve your mental health, at least you’ll get to breathe in some cleaner air. The USDA’s Forest Service has data demonstrating that nearly 670,000 cases of acute respiratory symptoms benefit each year from trees with over 800 deaths being prevented.
- Source: http://www.sciencedirect.com/science/article/pii/S0169204614002941