Growing the Urban Forest 1

Thursday, May 12th, 2016
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Climate change, like urbanisation, is happening rapidly. According to multiple government agencies worldwide, 2015 was the hottest year to date, taking over from 2014, and that trend is happening concurrently with rapid urbanisation.

By 2050, 66 per cent of the planet’s 9.7 billion people will reside in cities, according to the United Nations.

That sort of urban growth, ironically, threatens one of the key tools that’s crucial to making dense cities livable and healthy in a warming world: green infrastructure. Green roofs, living walls, bioswales, and urban forests offer myriad benefits to cities and their residents.

Growing cities, sadly, tend to be voracious beasts, consuming green space, parks, and the urban forest. Without a solid plan for maintaining green spaces, they’re all too easily lost to development. Thus, government mandates calling for the preservation and expansion of green spaces are necessary. Developers, and many cities, will have to be incentivized or required to maintain and even expand the area of green space as they develop projects to house the masses. In addition, green infrastructure projects should replace grey infrastructure projects whenever possible.

Green infrastructure represents one the most powerful approaches to both mitigate the effects of climate change and make cities more livable. Parks, for example, are multi-functional, providing recreation and social spaces while offering the benefits of cooling through evapotranspiration, reducing air pollution, and consuming carbon dioxide.

A recent paper delves into more specifics after the authors studied the topic in Hangzhou, China. The authors state that “Hangzhou is a rapidly growing Chinese coastal metropolis that is facing climate change impacts, including intense heat waves, flooding and increased severity of storms (e.g. typhoons and thunderstorms).”

Green infrastructure, the authors note, “is believed to possess considerable potential to adapt cities to some emerging climate change impacts such as heat island impacts, increased flooding, higher wind speeds and more episodic rainfall, especially in higher density cities where larger green spaces may be scarce.”

It’s important to recognize that green infrastructure is not simply green spaces, but consists of engineered and managed spaces designed for certain functionality.

“The key idea behind green infrastructure is that it is purposeful, intentional, designed, and deployed primarily for widespread public use and benefit,” the report’s authors stated.

Thus, we can think of green infrastructure as “parks, public green space, allotments, green corridors, street trees, urban forests, roof and vertical greening,” they wrote.

Australia’s governmental entities have started to get on board with these issues. Minister for the Environment Greg Hunt recently unveiled the new Clean Air and Urban Landscapes hub, which is part of the National Environmental Science Programme. The hub aims to help cities set urban targets for urban green spaces such as green roofs, green walls, and pop-up parks. In addition, the new hub will incorporate “Indigenous perspectives into urban design and planning,” according to the press release announcing the hub.

Governments in Sydney and Melbourne have also unveiled plans to foster green infrastructure. Sydney’s Urban Forest Strategy, for example, includes the ambitious goal of boosting the city’s urban forest up to 50 per cent by 2030. According to the project’s web site, in 2008, the city’s tree canopy covered about 15.5 per cent of the local area. That breaks down to:

  • 4.1 per cent in parks (15.6 per cent of total land use)
  • 4.9 per cent on roads (22.7 per cent of total land use)
  • 6.6 per cent of private land (61.7 per cent of total land use)

That last figure highlights a potentially thorny issue: the amount of the tree canopy that exists on private land and the necessity of increasing that amount as cities grow and densify. Can that be done through voluntary efforts? Not likely.

According to authors Joe Hurley, Ebadat Parmehr, Kath Phelan, Marco Amati,and Stephen Livesley, current land-use policies favor “dispersed piecemeal redevelopment of individual lots in existing suburbs, which produces relatively few new homes.”

This sort of incremental development is both low yield and destructive to the urban tree canopy.


All too often, trees are cleared to make way for housing.

The solution, the authors bluntly state, involves government action to continue “the contribution of private land to the urban forest. Existing and new approaches to achieving this outcome need to be considered – whether through local rules, government programs or incentive schemes.”

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  1. Barry B

    An absolute necessity for the types of high-density urban centres that Australia' s major cities are destined to become.