Your Health

City’s beautiful trees also enhance our health and well-being

Photo of banded elm tree.
Photo of Diana Doyle-Zebrun

Winnipeg Regional Health Authority
Published Friday, August 18, 2017

Winnipeg’s urban forest is under attack.

Dutch elm disease is on the rise, killing an average of 5,500 trees every year, according to a story in the Free Press last month. The cottony ash psyllid has also been busy this past summer, destroying a number of mancana and black ash trees this year.

Making matters worse is the fact that we are removing more trees due to Dutch elm disease and other issues than we are replacing them. The Free Press reported earlier this month that there were 9,419 trees removed in 2016 and only 2,757 planted.

Many Winnipeg residents have expressed concern about the loss of trees in our city, and with good reason. The elms, ash and other varieties of trees provide our city with an aesthetic charm that is hard to match.

But it is important to remember that these trees do more than add beauty to our community. They also provide us with many direct and indirect health benefits, which also contribute savings to our health-care system. In fact, a study published in 2014 suggests that trees in the United States generate as much as $6.8 billion in averted health care costs each year by helping people live healthier, happier lives.

Direct health benefits from trees include clean air and water, protection from the sun’s UV rays, and the positive mental health effects associated with the proximity to natural environments. Indirect benefits include a more active lifestyle linked to increased outdoor activity. Both the direct and indirect benefits are realized on hot summer days when people flock to our urban parks to take refuge in the shade and cooler temperatures where light physical activity is tolerable.

According to the World Health Organization, air pollution now kills around seven million people every year globally. Urban forests improve air quality by absorbing pollutants, intercepting particulate matter (e.g. dust, ash, pollen, smoke), and releasing oxygen through photosynthesis. In fact, the U.S. Environmental Protection Agency recognizes tree planting as a measure for reducing ozone, an air pollutant.

The health argument for investing in trees in the urban setting is even more convincing. In general, the more trees there are in an area, the more pollution those trees remove. But they also remove more pollution-per-tree in areas where population density is high, and the health value derived from pollution removal is highest in urban areas.

Over-exposure to ultra violet radiation (UVR) from the sun leads to skin cancer, and has been linked to cataracts and suppression of our immune system. In addition to protecting us from UVR, trees also help keep us cooler in summer.

Studies have shown that urban areas devoid of trees are often hotter than those with them. This discrepancy is called the “urban heat island effect.” Essentially, trees help keep us cooler by providing shade and releasing moisture into the atmosphere through a process called evapotranspiration.

Trees can also help mitigate the effects of global warming. The last few years have been the warmest on record, and this trend is expected to continue. Urban areas that experience rising temperatures from climate change can also expect rising morbidity and mortality as a result. Our communities need to find options to mitigate and adapt to these changes. Maintaining and adding to our urban forests, which provide shade and absorb the greenhouse gases causing climate change, will help.

Finally, there is a growing interest in the public health benefits from the presence of nature and trees in our urban environment. Research shows that urban forests create spaces for active and passive recreation, decrease physical and emotional stress and reduce violence. In one study, patients who were recovering from gall bladder surgery in a Pennsylvania hospital did so more quickly in room that had a view of trees than those looking out at a building. Another study found that residents living in greener surroundings reported lower levels of fear and less violent behavior. Studies such as these demonstrate that we're only beginning to understand the nature and magnitude of the possible mental health benefits of trees.

It is becoming increasingly clear that trees have the potential to help people live healthier and happier lives. Given these clear health benefits, it is well worth asking whether we should be doing more to protect and expand this critical public resource.

Dr. Lisa Richards is a medical officer of health with the Winnipeg Regional Health Authority. This article was originally published in the Winnipeg Free Press on Friday, August 18, 2017.

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