Numerous studies have demonstrated that the presence of trees in urban settings can improve mental health by reducing stress — living in areas with more green space correlates with lower levels of the stress hormone cortisol. On top of that, trees and green spaces are linked to less negative thoughts, less symptoms of depression, better mood (self-reported), and increased life satisfaction. As you might imagine, one study found that doctors prescribe fewer anti-depressants in urban areas that have trees! 

In the contiguous United States, urban trees remove an estimated 711,000 metric tons of air pollution every year. This is important because air pollution in the form of particulate matter (like ozone, carbon monoxide, polycyclic aromatic hydrocarbons, nitrogen dioxide and sulfur dioxide) is linked to a range of human health conditions including bronchitic symptoms, increased risk for glaucoma, heart attacks, changes in vascular function, autism, high blood pressure, cognitive development problems in children, heart failure and increased mortality.

In a warming world, one of the most pressing threats to human health is the increase in heat and heat-related health problems. This is especially prevalent in cities, where the Urban Heat Island effect combines with heat waves to create dangerous temperature spikes. Well-planned urban tree plantings can help relieve some of the heat pressure on urban dwellers. An analysis of 94 urban areas around the world shows that trees have a significant impact on temperature, and are responsible for, on average, 1.9°C of cooling in a city. In fact, they can reduce temperatures by up to 9°C, a big deal in areas where temperatures already spike over 100°F.

While it may seem counterintuitive to include the economy on a list of health benefits of trees, a strong local economy means more access to vital, life-saving resources like fresh, healthy food and adequate healthcare and services. While  infrastructure degrades over time, trees only gain value as they mature, improving property values along with them. Higher property values means stronger neighborhoods and more vibrant communities that feel safe and encourage people to get outside!

Research has shown that stress levels, concentration and intrinsic motivation influence a child's success as a student. Green environments, like trees, are related to reduced symptoms of ADD and ADHD — and studies have shown that children with views of trees are more likely to succeed in school. This can especially help those with information processing issues, behavioral problems and  attention deficit/hyperactivity disorder symptoms.

A view of trees can help hospital patients recover faster by reducing diastolic blood pressure and stress. In fact, studies have found that just 3-5 minutes spent looking at nature can help reduce anger, anxiety and pain, inducing relaxation. And as we know, stress plays a big role in our overall health and healing — and too much of it can weaken our immune system. So it should come as no surprise that time spent immersed in or even just looking at nature can help reduce recovery times for patients.

Residents of tree-lined communities feel healthier and have fewer cardio-metabolic conditions than those that live in less green areas. Among other factors, this can be attributed to the stress-relieving properties of trees — and the fact that regularly seeing them tends to encourage more regular physical activity in the great outdoors. All of which helps to keep our hearts healthy and strong. 

The presence of trees can help people with neurodegenerative diseases. Research into the link between nature and dementia are still at their early stages but the results are promising: during a 10-week woodland activity program for patients with early stage dementia, woodlands were found to promote mental wellbeing and provide a meaningful, purposeful sensory experience. These experiences not only improved spatial awareness, but also helped patients regain a sense of self.

Well-maintained neighborhood and street trees are associated with improving the social capital and ecology of communities, reducing violence and aggression in households and limiting criminal activity in neighborhoods. In one study, they found that when Ash Trees died off in Cincinnati, Ohio (due to the emerald ash borer) crime increased across the city. 

The idea that trees can improve food security and promote well-being is nothing new. Well planned urban orchards (or urban food forestry) can be an efficient way to provide free or low-cost, nutrient-dense food to people who need it. In New York City, 88% of the street trees grow medicine and food for city residents.

Stormwater runoff can increase people’s exposure to pollution, but trees intercept and filter stormwater, improving the water quality of runoff. With less contact with pavement, stormwater that has been absorbed and released by trees is cooler and has fewer pollutants when it enters local waterways.

Not only do trees absorb harmful chemicals, they also release beneficial ones. In studies of participants who been exposed to phytoncides (chemicals released by trees and plants), their immune systems benefited. In particular, the study observed an increase in natural killer cells (cells of the innate immune system). 

Since Natural Killer cells can kill tumor cells by releasing anticancer proteins, and forest bathing boosts our immune systems, forest visits may have a preventive effect on cancer generation and development.

Studies have shown that when we’re exposed to nature, even for just a short time, our parasympathetic nervous system gradually takes control, lowering our blood pressure, pulse rate, inflammation, and cortisol levels and elevating our moods. As a result, we can experience increased vigor and decreased depression, anxiety, fatigue, and mental fog. Simply put: forests help us stay happy, relaxed, and well. 

Humans have been enjoying the medicinal benefits of trees for thousands of years — and with good reason. Forests provide a rich reserve of compounds that are key ingredients in 25% of all medicines. Tree and plant extracts contain a variety of bioactive compounds that help with everything from managing pain to staunching bleeding, sterilizing wounds, strengthening our immune systems, soothing our nervous systems and more. 

Forest biodiversity helps to combat malnutrition and disease within vulnerable populations across the globe. Forest food, including fruits and nuts, wild leaves, palms, wild roots and tubers, mushrooms and insects, provide a safety net in lean times. Forest food can also add nutrients that people might not otherwise get — and may help them survive in times of environmental or geopolitical instability like war, famine or drought.