Trees soothe us. They welcome us into the cooling shade of their leafy canopies and encourage us to forget about our troubles. After a stressful day, we feel calmed and restored in their presence. But the idea that trees make us feel good isn’t merely wishful thinking. There’s a growing body of scientific evidence indicating that trees actually do help us live longer, healthier, and happier lives. Here are some of the most significant studies that have linked trees to human health and wellbeing in real and measurable ways.
A view of trees helps patients recover quicker from surgery.
One of the first studies to link trees to human health was a revolutionary study by environmental psychologist Robert Ulrich in 1984. Dr. Ulrich investigated patients at a Pennsylvania hospital who had undergone gallbladder removal surgery. While they recovered, some patients had a window view of trees from their hospital bed while others looked out at a brick wall. Dr. Ulrich found that the patients with the tree view healed an average of one day faster, needed less pain medication, and suffered fewer post-surgery complications when compared to those who had only the brick wall to look at.
Trees clean the air, saving more than 850 American lives per year.
A national study by the U.S. Forest Service and the Davey Institute in 2014 examined the role trees have in cleaning the air we breathe. Trees are especially valuable in ridding the air of pollutants like nitrogen dioxide, ozone, sulfur dioxide, and fine particulates such as ash. Because of this service that trees provide, the researchers estimated that 850 lives are saved each year in this country, and 670,000 incidences of acute respiratory symptoms are prevented. The dollar value is nearly $7 billion in health care savings.
People that live near many street trees report being healthier than those with few trees nearby.
Researchers at the University of Chicago published an interesting study in 2015 showing that residents of Toronto, Canada, who lived on tree-lined streets had fewer cardio-metabolic conditions, like heart disease and diabetes, and had a higher self-reported assessment of their health. Do people in leafy neighborhoods walk or exercise outdoors more, or is there some other factor at play? The researchers aren’t sure, but the correlation was strong. The planting of ten or more trees on a block brought about the same improvement in the average person’s health status as would have occurred had the person made $10,000 more per year or become seven years younger!
The loss of millions of ash trees in the midwest due to the emerald ash borer is associated with 15,000 cardiovascular disease deaths and 6,000 lower respiratory disease deaths.
This study, published in 2011, encompasses the 15-state area where the devastating beetle had struck by that time. Assuming that a massive die-off of trees would result in more pollutants in the air, and thus more human health problems and deaths than normal would likely occur, researcher Geoffrey Donovan examined medical records in the affected areas to look for a rise in pollutant-related deaths. He did indeed find 15,000 more cardiovascular disease deaths and 6,000 more lower respiratory disease deaths than normal. Donovan does not assert that correlation necessarily equals causation, but this study is one more bit of evidence pointing in that direction.
Mothers who live in areas with extensive tree canopies are less likely to give birth to underweight babies than mothers in areas with fewer trees.
This study, also published by Geoffrey Donovan in 2011, dealt with pregnant women in Portland, Oregon, and examined the correlation between the birthweight of their babies and the amount of trees around their homes. Even after accounting for the women’s ages, incomes, and all the other obvious factors that could influence their children’s birth weights, women in leafier neighborhoods were less likely to have underweight babies than women in other areas. It’s possible that the presence of trees has a calming influence on mothers-to-be, and the lack of stress they experience leads to healthier babies, although more research needs to be done on this seldom-studied topic.
All other things being equal, areas of a city with more trees have less crime than areas with few or no trees.
In 2012, researchers from the University of Vermont published a study from Baltimore, Maryland, showing a link between trees-lined streets and a decrease in crime. On average, a ten percent increase in tree canopy corresponded with a roughly 12 percent decrease in robberies, burglaries, thefts, and shootings.
The 2012 results in Baltimore affirmed a classic 2001 study at Chicago’s Robert Taylor Homes, which was the largest public housing complex in the world at that time. That study revealed that within the development, buildings with many trees and other greenery were the site of 48 percent fewer property crimes and 56 percent fewer violent crimes than identical buildings with little or no landscaping. It was also discovered that the residents who lived in buildings surrounded by trees were more likely to know and socialize with their neighbors, like where they were living, feel hopeful about the future, and feel safe in their homes than others in treeless surroundings. They were also less likely to engage in violent behavior.
A walk among the trees eases brain fatigue.
A 2013 study from Edinburgh, Scotland, made use of a new device—a portable EEG unit small enough to carry in a backpack. Researchers hooked subjects up to the machines and sent them on a walk to evaluate the brain’s response to strolling through different environments. Specifically, they were looking for “brain fatigue,” a syndrome we all feel from time to when being bombarded by demands and tasks. These researchers were interested to see if walking among trees could calm overstimulated brains. Sure enough, when subjects walked through a park-like area, the EEGs showed their brainwaves becoming much quieter.
Jogging among the trees has greater mental health benefits than jogging at the gym.
A 2012 study from Glasgow University indicates that if you like to jog, walk, or cycle, doing it outside in a forest or on a tree-lined sidewalk may give you additional mental health benefits over exercising in a gym. Professor Richard Mitchell found that subjects who engaged in physical activity in the natural environment experienced a 50 percent improvement in things like stress levels and mild depression over those who worked out indoors.
Japanese forest bathing can boost mental and physical health.
In Japan, the practice of “forest bathing,” or shinrin-yoku, is a popular way to de-stress. It involves simply spending some time among the trees, walking in the woods, inhaling the scents, listening to the birds, and appreciating nature with all of your senses. To tree lovers coping with hectic lifestyles, this practice needs no formal sanction, but Dr. Qing Li of Nippon Medical School in Tokyo has given forest bathing further credence with scientific studies that prove its effectiveness. A number of these experiments have shown forest bathing has the ability to reduce subjects’ levels of anxiety, anger, and depression, and the practice has also been shown to boost the immune system.
The intersection of trees and human health
The science of trees and human health is a young science, and we have only begun to explore how trees affect physical and mental well-being. However, it is clear that trees are more than simple and pretty things that enliven landscapes. Trees have the power to heal us, soothe our frazzled nerves, clean the air we breathe, and, in some cases, save our lives. As the scientific literature grows, we’ll learn more about these and many other gifts these gentle giants can give to us when we make trees a part of our lives.