2019 was Australia’s hottest and driest year on record.
Studies show trees significantly reduce temperatures. So by planting more trees in our cities and towns we can adapt to climate change.
Urban areas get hot
Urban areas are typically hotter than the countryside. That’s because when we build cities we remove trees and pave over waterways. And the building materials we use, like concrete and asphalt, absorb heat and release it slowly at night.
A study by the CSIRO found in summer Canberra’s urban areas were up to eight degrees hotter than surrounding rural areas.
Tiny forests battle climate change
In 2020, The Climate Factory built its first tiny forest or micro-forest in Downer in the Australian Capital Territory. This weeny forest occupies just 450m2 of suburban parkland.
The tiny forest is modelled on the Miyawaki method. The Miyawaki method plants native plants densely which leads to fast growth. The layers of native plants improve local biodiversity.
However, Edwina Robinson founder of The Climate Factory, realised she needed to take a different approach to climate change. Robinson decided not to use local native trees in the tiny forest. Instead she experimented with growing trees from hotter and drier climates. Plus she integrated simple water harvesting methods to direct water deep into the soil.
Australian National University tree study
In 2019, the Australian National University released a study showing the trees most likely to survive a hotter, drier Canberra. Top of that list was the Kurrajong, Brachyciton populneus.
The signature tree of Canberra’s tiny forests
In 2020, Robinson worked with local community to build a second micro-forest – the Watson Micro-forest. The Kurrajong has become the signature tree in both the Downer and Watson tiny forests.
the Banksia St, O’Connor wetland and are around 10 years old.
The Kurrajong is a sturdy evergreen Australian native tree with green glossy foliage. It grows slowly and may only reach four metres high in 10 years. Although this tree grows naturally in the Canberra region, The Climate Factory sourced plants from a nursery six hours north of Canberra. This nursery experiences temperature extremes of 49°C in summer and -9°C in winter. So these trees are likely to thrive in hot and dry urban environments.
As well as planting Kurrajongs, a number of other native trees are being trialled. The list includes the Queensland Bottle Tree, She-Oak, Allocasuarina and Silky Oak.
Ngunnawal use of the Kurrajong
The Ngunnawal people have lived in the Canberra region for tens of thousands of years. They used the bark of the Kurrajong to make string and rope. Kurrajongs have hard dark brown seed pods. The pods were turned into children’s toys. And inside the pods are seeds which are edible when roasted over a fire.
Does planting densely cool the landscape?
Robinson says she ordered temperature and humidity loggers to install into the micro-forests in 2022. Data from the loggers will be retrieved with smart phones. She will test if the dense planting of a micro-forest cools local temperatures.
To compare different planting approaches, one logger will be placed within the micro-forest and another one in a mature park tree with grass underneath. Time will tell if the dense planting cools the landscape. Robinson, says the inclusion of water harvesting should help keep temperatures down.
Resources
How to build climate-cooling micro-forest in 8 steps – video
Hi Edwina … my late lecturer in Landscape Architecture when it was still the CCAE, Glen Wilson, was a disciple of Edna Walling and spoke often about her and her work. I now live in Bundanoon, slightly warmer than Canberra, in a house with a large garden. I’ve noted how poorly the Silver Birches are performing here. Planted by the previous owner at least 20 years ago they attained a reasonable height but have now deteriorated considerably. I’ve removed one but three others need to be replaced. Two Weeping Silver Birches are, however, still doing quite well. Recently, I found in the Bundanoon Garden Club library a book on Edna Walling which contains images of her classic watercolour plans. The club, sometimes said to be the largest garden club in the country, will celebrate its 50 year anniversary next year with year-long activities.
Hi Jim, Thanks for sharing your story. I’d be interested to hear what trees are doing well. We are finding trees like Japanese Maple get their leaves fried by the hot dry winds. I also have a garden at Moruya, near the NSW south coast, Japanese Maples thrive here.
My mature Japanese maple died this summer just gone. I’ve never watered my garden, and it’s never been and issue. It was too late for the Japanese maple when I noticed. I don’t know how old it was, but its fully grown and my other mature tree is 60 years old, so it may be similar. I wouldn’t plant another Japanese maple now. They aren’t made for that kind of heat.
Hi Summer,
I would only use a Japanese Maple in a position sheltered from hot afternoon sun and drying winds and where I could provide irrigation.
Cheers,
Edwina
Thanks for this list. I wonder what your view us on Liquid Amber trees? Our 60 year old tree is doing well, but I am wondering if you think it would be fragile in years to come? Is it doing well because it is mature, and would younger trees suffer? Will it continue to do well, or become stressed? I would love to know what you think
Hi Summer,
I’ve checked Pryor and Banks (1991) classic ‘Trees and shrubs’ of Canberra. They don’t say how long Liquidambars last. Nor does the ACT Government’s fact sheets. I’d suggest deep watering for trees over summer. If you want an authority on trees you might want to check with an arborist. We have one in our unit complex in Lyneham that was looking pretty bad – as well as deep watering it was suggested to give diluted seaweed tonic.
Cheers,
Edwina