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New housing subdivisions, smaller yards and a dependence on air conditioning have resulted in a 30 per cent decline in Australian residential trees in the past decade, leading to hotter neighbourhoods and increased energy costs.

The dramatic loss of suburban trees has led to UniSA environmental researchers calling for new national planning policies to mandate the inclusion of trees in any development or housing design.

Qualified architect and UniSA PhD candidate Mina Rouhollahi said a recent study of 90 Australian residential suburbs shows tree-inclusive gardens and yards provide up to a 30-metre buffer around each land unit during summer heatwaves.

“Deciduous trees, in particular, provide summer shade, while their bare branches allow heat to penetrate into the house in winter,” Rouhollahi said.

“Local government focuses on public parks and urban forests but it’s the residential trees that make a significant difference to home energy costs. Also, private land tree planting provides a better environment for children, improving urban aesthetics and increasing home values.”

Rouhollahi and her UniSA colleagues, including supervisor Professor John Boland, have designed an optimal tree strategy for different housing configurations, nominating specific tree types, tree volumes, and correct placement to achieve maximum benefits.

Boland said there needs to be a more cohesive urban planning approach to compensate for residential tree loss in recent decades and to regulate heat as well as curb energy costs.

The strategy is outlined in a new paper which incorporates all seasons and microclimates, allowing planners, developers and designers to adopt the tree options that suit specific environments.

Their research recommends five optimal tree arrangements depending on deep soil availability and space.

The researchers’ proposal aligns with the latest IPCC report recommending increased space between houses to allow for more trees, as well as utilising reflective building materials.

The report said taking these steps could significantly decrease urban heat, reduce the reliance on electricity, and thereby cut blackout risks.

A major challenge is changing Australian attitudes, increasing the focus on home energy efficiency through appropriate tree planting, double glazing and better house design, and moving away from air conditioning reliance.

“Australians have the power to influence the design process, requesting tree allocation when building or buying their home, in the same way they insisted on a double garage in the 1990s,” Rouhollahi said.

“Redesigning our homes with trees in mind will better serve residents, cities, and the environment. Trees have numerous benefits: they shield us from the sun, provide wind protection, reduce stormwater runoff, passive cooling and natural ventilation.

“The net result is a more energy efficient home, lower energy costs, reduced air conditioning, CO2 emissions and less polluted air.”

Current residential development policies rely on public and communal open spaces to compensate for the lack of trees in private yards. Yet, this does not provide energy savings, the researchers said.

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