Imagine a drug that could lower the rates of heart disease, anxiety, stress and depression, prolong lifespan, strengthen social cohesion, encourage more physical activity and promote recovery from surgery and strokes.

Such a wonder drug would be the most prescribed remedy in the world. Of course, there is no such magical cure, but you could get the same effects simply by planting a tree.

Although it may seem far-fetched, recent research suggests that greenness can promote human health and well-being. People who live in green areas have lower levels of stress, anxiety and depression and they report lower levels of anger and aggression. Residents of areas with more vegetation are also more active and are more likely to interact with their neighbors. Not surprisingly, those who live in greener areas report stronger social ties and better social cohesion.

Astonishingly, the rates of total mortality and mortality due to heart disease are 12-15% lower in those who live in areas of high greenness. In a recent study, a gradual loss of ash trees in the northern United States by the ash borer beetle was found to be associated with a progressive increase in cardiovascular mortality, suggesting that in communities where trees die, people die as well.

Not only does nature seem to enhance the well-being of people, it also improves the health of the neighborhoods and cities they live in. Greener neighborhoods have lower crime rates and they are more resilient to flooding. Living in green areas even compensates for poor health outcomes due to economic inequality. Some estimates suggest that having 10 more trees per city block improves health in ways comparable to an increase in annual income of $20,000. Large trees and shrubs decrease air pollution, as they capture airborne particles and other harmful pollutants. There is even evidence to suggest that vegetation mitigates climate change, as well as climate variations and events.

The density of trees in major cities
Image: Treepedia

The age of the forest city

Recognizing the widespread benefits of nature, many cities are now devoting significant resources to increase urban greenness. There are attempts to create vertical forests in downtown high rises and to develop entire forest-cities, blanketed by trees. However, this unbridled enthusiasm may be premature.

Creation of far-flung leafy suburbs increases the need for automobile transport, which could worsen air pollution. Lollipop trees lining highly trafficked street canyons trap air pollutants, and many trees and plants generate allergens and chemicals that contribute to air pollution.

Enthusiasm for “going green” isn’t enough; we have to first learn how to interface with nature. We have to identify which trees are more conducive to health, which ones produce low allergens, which plants best support biodiversity, minimize storm surges and decrease air pollution. Where, and in what quantity and configuration, trees reduce pollutants and mitigate noise, all without being obtrusive or unsettling.

If nature is to be a wonder drug that cures many of the ills of modern society, it must be submitted to rigorous clinical trials, just like any other medicine.

Appraisals of the true costs and benefits of greenery could not only inform urban design and guide public policy, it could also strengthen the rationale for a system of subsidies and taxation, e.g., a city tax on tree removal and a tax credit for tree planting. However, to coordinate the greening of cities worldwide, we need a global initiative. We have to develop commonly accepted protocols for assessing the health and environmental impact of future, as well as current, greening initiatives. Harmonization of such efforts and sharing of protocols would optimize the utilization of current assets. This will be particularly helpful to resource-poor countries that now seem destined to bear the brunt of the epidemics of non-communicable diseases, environmental degradation and air pollution.

Fighting unhealthy cities

When it comes to greening cities, we have no other choice. Our natural resources are being rapidly depleted, and environmental degradation is threatening our well-being. Modern cities are replete with pollutants, traffic and noise; urban features of transportation, labour-saving devices, passive entertainment and fast food have created environments that promote non-communicable diseases (NCDs) such as obesity, diabetes, heart disease, depression, dementia and cancer.

These unhealthy urban habits have permeated rural areas as well. As a result, in the United States, nearly 70% of the adult population is overweight and 40% obese. The rates of heart disease, which have been declining, are now beginning to rise. By 2030, 40.5% of the adult population in US is likely to have some form of cardiovascular disease.

The situation is much worse in the developing world – where the NCD epidemic is projected to cost $21.3 trillion over the next two decades, a cost nearly equal to their current total economic output ($24.5 trillion). This high disease burden is likely to spread poverty and spur massive immigration to the developed world, which is ill-equipped to deal with its own health problems and aging populations. Although plants and bushes in cities may not extinguish crime and heart disease or prevent climate change, neutralization of these ominous threats, even in a small measure, will be worth the effort.

Maybe nature is a wondrous drug – not only of remarkable potency but of incomparable beauty as well.