Heard the chainsaws lately? Next time you are thinking about lopping that tree in your yard or complaining to council about that tree on your verge, stop and inhale deeply whilst taking a moment to consider just a few of the more contemporary facts associated with the quality of the air that we breathe, vehicle emissions, because mostly we all indulge in the luxury of driving a car, and the density of the urban tree canopy.
George Crisp the West Australian chairman of Doctors for the Environment Australia, writing for the Sydney Morning Herald, recently declared that outdoor air pollution is a silent killer, with the Australian statistic for deaths caused by polluted air sitting at about 2 percent. Doesn't sound like much until quantified against deaths caused by motor vehicle accidents and you guessed it, pollution trumps it in as the winner. He goes on to say that more people are dying annually from air quality in Australia than from motor vehicle accidents and explains that the ingredients of air pollution are noxious gasses and tiny suspended fine particles. The latter coming mostly from vehicle exhausts. Crisp explains that its the fine particles that pose the real risk as they penetrate deep into our lungs and enter our blood stream, causing all sorts of health effects from every day exposure. These include heart disease, asthma and not unlike smoking the tiny particles are a known cause of cancer. Add vulnerabilities, like those inherently associated with early childhood, or old age or those unlucky enough to have existing heart and lung issues and the outcomes associated with every day life transactions, such as peak hour traffic flow, can be choking both to the individual and to society. In a recent report, 'The Hidden Costs of Asthma' Deloitte Access Economics, has found that the direct health care costs of asthma is 1.2 billion dollars, noting that that is just asthma and does not account for heart disease or cancers.
Good new is on the horizon though with the University of Technology Sydney, releasing co-joint findings in collaboration with the City of Sydney and a host of others, about the importance of trees in our urban environment, the places that most of us live on a daily basis. For the first time this collaborative has provided evidence that higher levels of urban forestry are associated with lower levels of air pollution, specifically the fine particles that come mostly from vehicle emissions. Those mentioned above, which are clearly insidious to human health. The project supervisor, Dr Fraser Torpy says that;
"Trees and their canopies help with the deposition and dispersal of particulate pollution that cause serious respiratory diseases, such as asthma, and several cancers. Future research could help identify the best types of trees to plant, where to plant them and in what density.
So next time your thinking that that tree has got to go or you are about to pick up the phone to ask your local council member to have a branch lopped here and a branch lopped there, think again because not only did the study find that trees really are the urban lungs for all life, it found that not all greenery is equal. Not surprisingly grass doesn't rate at all, with the benefit of reducing air pollution and fine particles only being derived from trees and the tree canopy.
Wow, finally someone is talking and studying the tree canopy and the importance of this in mitigating the health effects of vehicle emissions. However, the role of the canopy isn't limited to this. Amongst other things the structure of the canopy also acts as a vital catalyst in reducing the urban heat island effect, meaning that the canopy equals shade and the provision of dense shade equals cooler surface temperatures in urban areas. All this equates to a healthier urban habitat for all. Take for instance data from United States Environmental Protection Agency in 2013 which indicates the extent of heat mitigation provided by appropriate vegetation;
"Trees and vegetation lower surface and air temperatures by providing shade and through evapotranspiration. Shaded surfaces, for example may be 11 - 25°C cooler than the peak temperatures of unshaded surface materials. Evapotranspiration along or in combination with shading, can help reduce peak summer temperatures by 1 - 5°C."
Data which is supported by the Victorian Centre for Climate Change Adaptation, who highlights the thermal comfort benefits associated with 'greening' our urban environment and discusses the specific type of architecture required in a tree species to obtain dense shade provision.
At the end of the day, be it mitigating public health concerns associated with vehicle emissions or the public health concerns associated with urban heat, it all adds up to a certain quality of life and how the structure and function of our urban environment has a significant influence on ambient, liveable and healthy conditions for all. So next time you feel tempted to pick up the chainsaw - stop for a moment, take a deep breath, stand in the shade and think about the facts!
Interested in some of references? You can read them here.
- United States Evnironmental Protection Agency, 2013, Heath island effect:Trees and vegetation, Available,<http://www.epa.gov/heatisland/mitigation/trees.htm>.
- University of Technology Sydney, 2015, More trees please - greening cities reduces air pollution. Available, <http://newsroom.uts.edu.au/news/2015/09/more-trees-please-greening-cities-reduces-air-pollution-0>.
- Hunter-Block, A,. Liversley, S., & Williams, N, 2012 Literature Review: Responding to the Urban Heat Island: A review of the potential of green infrastructure, Victorian Centre for Climate Change Adaptation Research. Available, <http://www.vcccar.org.au/sites/default/files/publications/VCCCAR%20Urban%20Heath%20Island%20-WEB.pdf>