Nov 082016

Speaker: Tooba Shakeel (LEAF)
Written by: Sheena Jain & Esha Jain

Taking a stroll at the park, gardening in our backyards and cruising down the road, we have all done at least one of these things at some point in our lives but what do all of these activities have in common? In all of these scenarios you will see trees and tree-related plants like wildflower and shrubs, each of which encompasses the “urban forest. In short, the urban forest is a collection of trees that grows within a city, town or suburb. The urban forest is so important because it combats climate change and provides environmental, health, community as well as ecological benefits, to name a few.

The urban forest decreases air temperatures by providing shade and allowing water to evaporate from tree leaves. This in turn reduces household energy consumption for cooling from 10-50%. Additionally they lower the urban heat island effect, which is a phenomenon in which temperatures in urbanized areas are significantly warmer compared to surrounding rural areas due to human activities. Urban trees also protect and improve the quality of air, water and soil. Air quality is recuperated by the tree’s ability to trap pollution particles that cause breathing problems. In addition to providing oxygen they absorb and store carbon dioxide, removing it from the air. This also helps achieve carbon mitigation. Urban trees have been found to contain approximately four times more carbon than trees in forests. Their shade also helps decrease ozone emission released from cars. Trees improve water quality and intercepts rainfall, resulting in reduced storm water runoff, thereby preventing high amounts of stress on the grey infrastructure. They also store water and release it slowly in order to avoid the development of floods. Furthermore urban forests remediate contaminated soil and decrease erosion.

   Urban trees have been shown to reduce the billions of dollars spent on healthcare costs each year. This is achieved by improving physical and mental health. Studies have demonstrated that individuals are more likely to spend time outdoors being more social and active when trees are around. The view of trees from hospitals is also likely to decrease recovery time and hospital stays. It has also been seen to improve attention at school and work due to people feeling more satisfied in their environment. Additionally forest bathing therapy has been proven to provide calming neuropsychological effects within the nervous system. Urban trees have also been shown to have positive effects on hormone levels, and decrease stress.  Other health benefits of the urban forest include providing UV protection and decreasing asthma. Their ability to reduce noise pollution by acting as sound barriers, not only provides health benefits, by preventing hearing loss, but also provides community benefits, by creating a more pleasant atmosphere in which to live.

 Neighbourhoods that contain more trees and green space have an increased sense of connectivity and community. Urban trees can increase residential property values by up to 30% and business traffic in commercial areas as they provide a high aesthetic value. There has also been a correlation between decreased crime, graffiti and vandalism seen in these communities. They also improve road safety in these areas by calming traffic and by decreasing road rage, accidents as well as road maintenance in these communities. Not only is the urban forest beneficial to the lives of humans but also to wildlife.

Toronto urban forests provide the equivalence of more than $28.2 million in ecological services per year. This is achieved because they restore ecosystems by providing habitat and a source of food for urban wildlife.  They also act as an ideal location for migrating birds and butterflies, in addition to supporting pollinator biodiversity.

            Although urban forests are so valuable to us environmentally, physically, mentally, cognitively, regionally and ecologically, they are facing a large amount of stressors in Toronto. There is less area for tree’s to grow both under and over ground, due to low soil volumes and crowded areas. Improper care and watering has led to poor quality soil which lacks adequate amounts of nutrients for trees and plants to extract. Invading pests like the emerald ash borer are also responsible for creating less ideal conditions for urban forests in Toronto.

            Since it would cost Toronto around $7 billion to replace all of their trees, the best way to improve the quality of urban forests other measures need to be taken. 60% of trees are located on private property where there may be a lack of control, therefore these individuals should be educated about ways to establish and maintain suitable growing conditions. These include planting more trees of diverse species and watering tree roots 2-3 times per week, with a slow trickle water flow. Additionally trees should be mulched in a doughnut shaped ring to prevent erosion caused by direct contact between the mulch and the tree base. Mulch trees replenish the nutrients in soil and should be soaked for 10-15 minutes. Newly planted trees are especially benefitted by these practises. Furthermore, it is important to protect the soil and remember that trees have roots, which grow outward instead of downward. These roots should be protected 2-4 inches below the soil.

Discussion questions:

1)   What is the connection between urban forests and reducing ADHD symptoms?

A study examining the relationship between children with ADHD and the urban forest was conducted by Frances Kuo and Andrea Faber Taylor. Both were specialists in psychology and environmental science at the University of Illinois. Their data showed that children with access to green spaces for leisure and activity demonstrated milder ADHD symptoms than children without.

The theory of attention restoration was a potential explanation for these findings. This theory focuses on directed and involuntary attention. Where directed attention refers to engaging in deliberate focus, such as during activities like reading, writing or driving. On the other hand involuntary attention describes periods of automatic focus, which occurs when walking on a busy sidewalk or when getting dressed in the morning.

Directed attention is necessary to maintain productivity. It is a limited resource in everyone and is even further reduced in children with ADHD. Taking part in activities such as playing in areas surrounded by greenspace outdoors, allows children to replenish their capacity for directed attention. Spontaneous play on the other hand only enhances involuntary attention.    

2)   What studies have been conducted that demonstrate how urban forests decrease asthma exacerbations?

A group of researchers at Portland State University conducted a study to demonstrate how the urban forest decreases the effects of asthma and other respiratory diseases. The study placed 144 sensors in different areas across Portland and measured nitrogen dioxide levels associated with various sources of air pollution including traffic. The study found that because of the tree canopy’s present throughout Portland:

  • Children ages 4-12 avoided missing 7380 days of school from asthma-related exacerbations
  • Individuals of all ages avoided 54 asthma-related emergency room visits
  • Individuals >65 years of age had 46 fewer hospital stays due to respiratory illness
  • In total $6.6million were saved due to the health benefits of urban forests

The study concluded that the amount of tree coverage had a direct impact in removing nitrogen dioxide levels from the air, which in turn lead to fewer asthma and respiratory-related illnesses in these areas.

3)   What evidence exists that demonstrate how forest bathing therapy specifically benefits human health and well-being?

Dr. Qing Li a senior assistant professor at Nippon Medical School in Tokyo conducted many studies examining the effects of forest bathing on mood, stress levels and the immune system.

One study in particular used the Profile of Mood State (POMS) test to measure the association between forest bathing and physical and mental health. The investigation demonstrated that forest bathing trips increased scores for physical strength/health and decreased the scores for anxiety, depression and anger. Dr. Li’s research concluded that the risk of psychosocial stress-related illnesses may be decreased by engaging in habitual forest bathing.

Other studies measured natural killer (NK) cell levels in association with forest bathing, to determine its effects on immune function. NK cells are elements of the immune system that combat cancer cells. In these studies groups of men and women had their blood drawn before and after being sent to two-night/three day forest bathing trips, which included forest walks and staying in hotels within the forest. Lab results of these study subjects demonstrated increases in NK cell activity for 30 days after returning from their forest bathing trips. Additional analysis demonstrated an increase in NK cell activity for up to 7 days after returning from a day long trip of forest bathing. A potential explanation for the increase in NK activity observed by Dr. Li was in part due to inhaling air consisting of phytoncide (wood essential oils) such as α-pinene and limonene. These are antimicrobial volatile organic compounds produced by trees in order to prevent rotting and to provide protection against insects.            


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2)    “Climate Science Glossary.” Skeptical Science. N.p., n.d. Web. 23 Oct. 2016. (

3)    Intern, By Conrad Kabbaz Policy. “How Urban Forests Can Help Mitigate ADHD Symptoms – American Forests.” American Forests. N.p., 11 Aug. 2015. Web. 23 Oct. 2016. (

4)    Parallelus. “Not a Member Yet? Register Now and Get Started.” HPHP Central Forest Bathing Comments. N.p., n.d. Web. 23 Oct. 2016. (

5)   “Trees Help Prevent Asthma, Respiratory Diseases, Study Says.” Trees Help Prevent Asthma, Respiratory Diseases, Study Says. N.p., n.d. Web. 23 Oct. 2016.


6)    “Urban Forest.” Wikipedia. Wikimedia Foundation, n.d. Web. 23 Oct. 2016. (

 Posted by on November 8, 2016