Climate change is on everyone’s lips this summer. We’ve had bushfires, smoke haze, heatwaves, flooding, mass protests and a National Climate Emergency Summit, all within a few months. The search is on for solutions. Trees often feature prominently when talking about solutions, but our research shows trees are being lost to big developments – about 2,000 within a decade in inner Melbourne.
Big development isn’t the only challenge for urban tree cover. During the period covered by our newly published study, the inner city lost a further 8,000 street trees to a variety of causes – vandals, establishment failures of young trees, drought, smaller developments and vehicle damage.
Still, thanks to a program that plants 3,000 trees a year, canopy growth has kept just ahead of losses in the City of Melbourne.
Canopy cover is crucial for keeping urban areas liveable, shading our streets to help us cope with hot weather and to counter the powerful urban heat island effect. Trees can also be a flood-proofing tool.
Trees add beauty and character to our streets, and (so far) they’re not a political wedge issue in the ongoing culture war that is Australian climate policy. In short, they’re a very good idea, at just the right time.
Lessons for our cities
While Melbourne-centric, there are lessons in this study for cities everywhere. Robust policies to protect and retain trees backed up by clear financial incentives are valuable, as even well-resourced councils with strong policy face an uphill battle when development gets intense.
Our findings highlight that retaining and establishing young trees is especially difficult. This is troubling given these are the trees that must deliver the canopy that will in future shelter the streets in which we live and work.
Improved investments in how young trees are planted and how long we look after them can help. For example, in a promising local study, researchers showed that trees planted in a way that catches rainwater run-off from roads grow twice as fast, provided planting design avoids waterlogging.
Finally, in the context of rapid development, buildings themselves can play a positive role. Green roofs, green walls and rain gardens are just a few of the ways developments can help our cities deal with both heat and flooding.
There are plenty of precedents overseas. In Berlin, laws requiring building greening have resulted in 4 million square metres of green roof area – three times the area of Melbourne’s Hoddle Grid. In Singapore, developments must include vegetation with leaf area up to four times the development’s site area, using green roofs and walls. Tokyo has required green roofs on new buildings for nearly 20 years.
The solutions are out there, and urban greening is rising in profile. Recent commitments in Melbourne, Canberra and Adelaide are promising. Our study findings are a reminder that, even for the willing, we’ll have to take two steps forward, because there’s inevitably going to be one step back.