Urban forests: how trees can fight heatwaves and poor health

By David Donaldson

Thursday February 14, 2019

Queens Park, Moonee Ponds. Supplied by Moonee Valley council

Key points:

  • Planting trees can spell high return on investment for government
  • Several Melbourne councils have set urban greening targets
  • Moonee Valley’s planting program earns international acclaim

Climate change and urban development are heating up Australia’s cities. Planting trees is one solution being tried by Melbourne’s local councils.

Over the past century, heatwaves have killed more Australians than all other natural disasters combined.

And the problem is only going to get worse. This past January was Australia’s hottest on record; all five of the country’s hottest years have occurred since 2005. Just a few weeks ago Melbourne’s northern suburbs hit 46°c.

Urban life can exacerbate the effects of hot weather, as roads and concrete act as giant heat sinks and turn whole suburbs into massive ovens.

But tree cover can be a highly effective weapon against excess heat, reducing immediate surface temperatures by up to 20°c. A 10% increase in canopy cover across an area can drop ambient temperatures by 1°c.

Trees offer a surprisingly large number of other benefits, such as reducing flood risk, capturing carbon and other air pollution, providing habitat for fauna, improving mental health and encouraging people to do more exercise. Having a green vista appears to help patients who’ve just had surgery heal faster, while people who live in areas heavily affected by tree-killing diseases are more likely to die of heart or respiratory disease themselves.

Greenery may encourage people to linger on shopping strips and spend more money. And as fewer Australians have their own backyard, green public spaces will become more important.

The combination of all these factors means planting trees can potentially have a high return on investment for government.

Recognising this, several Melbourne councils have created urban greening targets. The City of Melbourne, which holds many of the city’s great parks as well as its highly urban core, is aiming to increase canopy cover from 22% to 40% by 2040. Melbourne has some great interactive maps and biodiversity resources available online — you can even send emails to individual trees.

The City of Moreland, home to the hipster haven of Brunswick, may be green in politics but has few big trees. But things are changing: it has committed to planting 5000 new street trees per year, and won a 2017 Premier’s Sustainability Award for its interesting work on urban heat islands, such as the thermal image below (the blue-green bits are the area’s few parks).

Moonee Valley’s urban forest initiative

Situated in the inner north-west, Moonee Valley is the latest council to be recognised for its efforts. It was recently listed alongside Lisbon as a sustainable environment finalist at the international Wellbeing City Awards, and is the only Australian city shortlisted in any category this year.

Unfortunately, many parts of Melbourne’s inner northern and western suburbs don’t have many big shade trees. Some areas are devoid of much shade at all during the hot summer months.

And while councils have been thinking about this problem for a few years now, the situation has deteriorated as backyard trees are cut down to make way for townhouses and apartments.

So Moonee Valley wants to reverse the trend. The council is planning to increase canopy cover from a baseline of 11% up to 30% in 2040.

“As our population grows and the urban environment becomes hotter and drier, the need for a green city that is ecologically healthy and environmentally responsible is pressing,” says Mayor Narelle Sharpe.

“The Enhancing our Urban Forest initiative will provide much-needed shade and cooling and better air quality which will encourage people to walk, cycle and visit their local parks, shops and surrounds.”

The council aims to increase the number of trees not just on its own land, but on areas owned by other levels of government and private property through a mix of protection, collaboration and community programs and education.

“We will see a diversity of vegetation in streetscapes, parks and reserves, greater protection for vegetation on private land and additional plantings where required. A diversity of trees also helps to ensure climate, pest and disease resilience,” Sharpe explains.

In 2018, the first year of the initiative, Moonee Valley put in around 2700 advanced street trees.

It’s supporting the 30% target through some innovative uses of technology. Remote sensing and spatial analysis will be used to track tree canopy targets and quantify and monitor changes. Tree canopy mapping is currently underway.

An ecological connectivity study has also recently been completed to establish a biodiversity baseline, identify monitoring indicators and prioritise land corridors.

There is also interest from other councils who would like to work together to establish a unified process to measure collective impact, Sharpe says.

Moonee Valley’s five-year planting program, currently being drafted, will “prioritise planting to areas of greatest need, based on absence of canopy cover, urban heat, social vulnerability, key active transport routes, biodiversity corridors, increased overall diversity of the tree population and other operational parameters,” the mayor explains.

Moonee Valley is also collaborating with other Western Melbourne councils, water corporations and the state government on Greening the West, a regional initiative that aims to deliver positive health and social outcomes in Melbourne’s western suburbs through urban greening.

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