By Dr. Mercola
It has long been suggested that spending time in natural outdoor environments may enhance human health, but researchers from the University of Chicago took this notion a step further by quantifying just how beneficial it is.
After reviewing a database of public trees and health records in Toronto, they revealed that living around an extra 11 trees per street lowers the risk of heart disease, diabetes, and obesity.1
The health benefits were equated to receiving an annual salary increase of $20,000, and those living near a greater density of public trees also reported significantly improved self-perception of health (how healthy a person perceives himself to be).2 According to the study:3
“We find that having 10 more trees in a city block, on average, improves health perception in ways comparable to an increase in annual personal income of $10,000 and moving to a neighborhood with $10,000 higher median income or being 7 years younger.
We also find that having 11 more trees in a city block, on average, decreases cardio-metabolic conditions in ways comparable to an increase in annual personal income of $20,000 and moving to a neighborhood with $20,000 higher median income or being 1.4 years younger.”
Why Is Living Near Trees Healthy?
Spending time in green spaces has psychological and physical benefits. Simply taking a walk in a natural area has been shown to decrease the pattern of negative thinking known as rumination, which is linked to an increased risk of depression.4 Those researchers noted:
“This study reveals a pathway by which nature experience may improve mental well-being and suggests that accessible natural areas within urban contexts may be a critical resource for mental health in our rapidly urbanizing world.”
Indeed, more than 80 percent of Americans live in urban areas,5 which can limit access to green spaces and potentially worsen public health. In addition to improving well-being, those living in a greener environment report fewer health complaints and better mental health.6
All types of green space – city parks, agricultural areas, forest, etc. – were equally beneficial. Cognitive function may also improve. In a study of 2,600 children between the ages of 7 and 10, those with greater exposure to green spaces, particularly while at school, had improved working memory and decreased inattentiveness.7
A 2014 study similarly found that children attending schools with greater amounts of vegetation scored higher on academic tests in both English and math.8 Not to mention, older adults who spend more time outdoors have less pain, sleep better, and have less functional decline in their ability to carry out their daily activities.9
Trees Reduce Air Pollution
From a practical perspective, another reason why increasing trees is good for your health has to do with their role in air pollution. According to the World Health Organization (WHO), ambient (outdoor) air pollution in both cities and rural areas caused an estimated 3.7 million premature deaths worldwide in 2012, the majority of which were due to heart disease and strokes.10
Trees have the potential to change that. Trees remove air pollution primarily by uptake of pollutants via leaf stomata (pores on the outer “skin” layers of the leaf).
Some gaseous pollutants are also removed via the plant surface. Once inside the leaf, the gases “diffuse into intercellular spaces and may be absorbed by water films to form acids or react with inner-leaf surfaces.”11
In a broad-scale estimate of air pollution removal by US trees nationwide, researchers found trees and forests in the US removed 17.4 million tons of air pollution in 2010, with human health effects valued at $6.8 billion.12
Although this pollution removal equated to an average air quality improvement of less than 1 percent, its effects on human health were significant, especially in urban areas. The health impacts included the avoidance of more than:
- 850 deaths
- 670,000 cases of acute respiratory symptoms
- 430,000 incidences of asthma exacerbation
- 200,000 school days lost
As you might suspect, most of the pollution removal occurred in rural areas (where tree cover can be as high as 88 percent) but most of the health impacts were within urban areas (where air pollution tends to be worse and population levels are higher).
Another study found that a 10-by-10 kilometer space (approximately six by six miles) with 25 percent tree cover in London could remove more than 90 tons of particulate matter annually, which would lead to the avoidance of two deaths and two hospital admissions per year.13
Trees Might Encourage You to Get Outdoors
Trees are known to promote physical activity among residents, yet another one of their charms. Better still, exercising outdoors among the trees has unique benefits above and beyond indoor exercise. One meta-analysis of 10 studies found that physical activity outdoors for as little as five minutes leads to measurable improvements in mood and self-esteem.14
There’s even research showing levels of the stress hormone cortisol are lower when people exercise outdoors as opposed to indoors.15
This can be invaluable among children too. Richard Louv, in his book Last Child in the Woods, even used the term “nature-deficit disorder” to describe behavioral problems he believes stem from spending less time outdoors.16
Plus, children who spent five to 10 hours a week outside developed a strong attachment to nature, a value that is important to both human development and well-being.17
Those who spent a lot of time outdoors also experienced a wealth of positive emotions, including peacefulness, happiness, and a sense of belonging to the world – pretty impressive benefits for simply spending time out amongst the trees!
How to Add More Trees to Your Backyard Environment
The authors of the featured study made a point of saying that “street” trees (or those in public spaces) had a more pronounced effect than private or backyard trees, but this is likely only because they’re accessible to more people. It certainly doesn’t downplay the importance of adding trees to your own backyard.
Every tree planted helps the environment, and trees around your home can increase your property value by more than 15 percent while improving your odds of a sale. Trees also do the following wonderful things for you and the environment:
- Decrease carbon dioxide and increase oxygen levels in the atmosphere
- Improve water quality and reduce erosion
- Give songbirds a home, and provide food for all kinds of wildlife
- Provide shade in summer and a windbreak in winter, thereby reducing your cooling and heating costs
- Beautifying your home and neighborhood, and adding curb appeal
6 Steps to Planting a Tree Properly
If you want to plant some trees but are not sure how to go about it, organic arborist and author Howard Garrett (aka, the Dirt Doctor) can end your confusion with his simple, straightforward steps to tree planting.18 Planting a tree the right way involves six basic steps:
- Dig a wide rough-sided hole
- Run a "perk test" for drainage: Fill the hole with water and wait until the next day. If the water level does not drain away overnight, you have a drainage problem. In this case, you might want to either choose another site or add some additional drainage.
- Prepare the root ball: Loosen the burlap at the trunk and remove it from the top of the ball. Remove any nylon twine or plastic covering, string, or wire mesh, since these materials do not decompose and can girdle the tree's trunk and roots as it grows.
- Set the root ball in the hole with backfilled soil
- Settle the soil with water (don’t stomp it down with your foot)
- Mulch the surface
According to Garrett, almost all trees planted today are being planted incorrectly. The most serious problem is when they are planted too deep. When the top of the root ball and the root flare are buried under the ground, hidden roots can circle and "girdle" the trunk, choking off nutrients and weakening the tree, which makes it susceptible to blowing over. Another problem is when soil comes up too high on a trunk, the covered bark tissue stays moist all the time and plant growth is dramatically slowed or even stopped. Garrett writes:
"Trees that are too deep can be uncovered with an Air Spade [a professional tool] or by hand, but the best solution is to plant trees correctly in the first place."
He also does not recommend staking, wrapping trunks or using other unnecessary and damaging techniques. As for when to plant your new tree, fall is a great time due to moderate temperatures and rainfall allowing them to acclimatize and grow strong roots before the heat and dryness of summer. Springtime planting works well too, depending on your region. So do follow the tips above, but don’t get too overwhelmed with the details. As Garrett said:
"People don't grow trees. Trees grow in spite of people. For the most part, trees are tough, durable and easy to plant and transplant if treated in a sensible and natural way."