AND QUALITY OF LIFE
Trees and the urban forest are a critical part of a city system and one increasingly important in combatting urban heat island effects and climate change.
I had lunch last month under a massively spreading plane tree. The dappled shade moderated the unseasonably punishing heat of what we want to believe is an Indian summer, but might just be an ominous harbinger of summers to come. We had just come through 9 consecutive days over 35C, which is a record for Melbourne at any time of year. This happened in March, beyond what should have been the end of our southern hemisphere summer, a summer that in our part of the world was the driest in 30 years, drier even than any of the summers during the 13 year drought that broke (temporarily?) in 2009.
It looks like our changing climate will become more like that of cities 200 miles inland – consistently hotter and drier summers, with the added burden of extreme weather events. Every city must bear its climatic burden: In our case it is extreme heat and drought, with the resulting threat of bushfires, in summer.
Our trees are not only part of what makes Melbourne’s urban environment so good, they contribute in a number of ways to the wellbeing of our city: They filter pollutants, moderate water runoff, provide habitat for birds and animals, sequester carbon, prolong the life of our built environment, and mitigate the effects of our urban heat island. They also play a critical role in wellbeing and mental health outcomes. All of these roles and more are important and are going to become increasingly so as our city heats up in the face of climate change.
Melbourne University’s Dr. Greg Moore says trees are “mature infrastructure assets’ providing ecological services that have yet to be properly valued and, once lost, would be difficult to replace”. He estimates the cooling effect of 100,000 mature urban trees – inner city Melbourne has around 70,000 – could save a city 3 million kilowatt hours of electricity annually. This represents around 3600 tonnes of saved carbon emissions, not to mention the 300 million litres of water that would have been used to generate that amount of electricity.
New York’s PlaNYC includes a well-publicised Public parks in PlaNYC that everyone live within a 10 minute walk of a public park and that streets be re-conceptualised as public space. As well as the obvious liveability benefits, there is a clear economic driver for this.
The plane tree I sat under last month is part of the legacy of exotic (that is, non-native) trees planted in the 19th and early 20th Centuries when our city fathers (they were, after all, almost exclusively men) were trying to create an antipodean version of a European capital. Our city has magnificent gardens filled with oaks, elms, planes, none of them native and, really, none of them properly suited to our climate, especially as it becomes hotter and drier.
The recent 13 year drought, which we seem to have forgotten about already, provided a pointed illustration of the challenge we face in maintaining our urban tree canopy. At the height of the drought, it was estimated that 900 trees were lost from public spaces in inner Melbourne in one year – triple the normal annual loss – with 40 per cent of the remaining trees under stress due to drought and water restrictions. The exotic trees are, of course, most at risk in this situation.
So what do we do about it? Trees, of course, take a long time to grow. You can’t simply rip a bunch of trees out and create a new canopy overnight. The City of Melbourne’s recently published CoM Urban Forest Strategy represents a comprehensive approach to this issue. It is based on estimates that 27% of its current tree stock will die in the next 10 years rising to 40% ten years after that. Its focus is on almost doubling the tree canopy and maximising species diversity to support resilience in the face of an increasingly harsh environment.
Much as I love Melbourne’s exotic trees such as the plane tree enjoyed at my recent lunch, I need to accept and embrace the reality of their likely loss over coming years and revel in the chances of sitting in the dappled shade of one of our native trees, equally magnificent in their antipodean beauty.
A version of this appeared at UBMFutureCities.