2019 was Australia’s hottest and driest year on record and ended in the Black Summer Bushfires. Alarmingly, four years later, 2023, was the world’s hottest year on record.
Knowing what action to take about a heating planet can be daunting.
A visit to the Australian National Botanic Garden rainforest gully in January 2019, convinced Edwina Robinson of the social enterprise, The Climate Factory that tiny or microforests could beat the heat. She recorded air temperatures in the carpark (37°C) and in the bottom of the rainforest gully (26°C) – a whopping 11°C difference.
Numerous studies confirm Robinson’s observation. So, by selecting the right trees coupled with appropriate maintenance, we can adapt to a hotter future. This might mean planting shade trees in your garden, growing a home microforest or starting a community microforest in your local park.
Urban areas are typically hotter than the countryside. That’s because when we build cities and towns we remove trees and concrete 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 2017, Canberra’s urban areas were up to eight degrees hotter than surrounding countryside.
Canberra’s tiny forests modelled on the Miyawaki method
In 2020, the social enterprise, 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 which plants native plants very densely (around three plants per square metre) which leads to fast growth. Not just trees are planted, but shrubs, groundcovers, climbers and strappy plants to improve local biodiversity.
The Miyawaki Method relies on surveying a local forest to mimic nature in miniature. However, Edwina Robinson founder of The Climate Factory, realised a different approach was needed in Canberra, Australia’s national capital.
Climate change models show Canberra is likely to be up to 2°C hotter on average by 2050 with 19% less rainfall. Weather events, including bushfires will become more extreme.
Robinson decided not to use Canberra’s local forest trees, like Eucalyptus in the microforests. Eucalyptus or Gum trees have a reputation for flammability. And she thought local residents would be anxious about Gums planted densely near their houses. Instead, she experimented with trees from hotter and drier climates, with low flammability, based on Australian National University (ANU) research.
Canberra’s microforests cool the landscape with water harvesting
A further departure from the Miyawaki method, was the integration of a water harvesting methods to direct water deep into the soil. Basically an underground water reservoir is created below plants which helps drought-proof trees so they can continue to function as an outdoor evaporative cooler.
Urban forest research shines spotlight on climate ready trees
In 2019, the ANU released a study showing the trees most likely to survive a hotter, drier Canberra. Top of that list was the Kurrajong, Brachyciton populneus.
Kurrajong, 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, Brachyciton populneus has become the signature tree in Canberra’s microforests.
What trees will be the hardiest?
The Kurrajong is a sturdy evergreen Australian native tree with green glossy foliage. It grows naturally in the Canberra region and may only reach four metres high in 10 years. Should you only choose plant stock selected from the local area?
The ANU research advises:
“When species have a wide distribution, choose provenances that reflect Canberra climate change future, i.e. hotter and dryer. For example, Brachychiton populneus, attempt to use seeds and nursery stock from provenances from areas west of Canberra with hotter dryer climates such as Griffith or Condobolin”.
For the Downer Microforest, Robinson sourced tubestock from a nursery north west of Canberra where temperatures top 49°C and plummet to -9°C.
As well as planting Kurrajongs, a number of other native trees were included, like the Queensland Bottle Tree, She-Oak, Allocasuarina, Silky Oak and Melia azederach and pioneer shrubs like Acacia.
Kurrajong important to Ngunnawal people
The Ngunnawal people have lived in the Canberra region for tens of thousands of years and used the Kurrajong for a variety of purposes. They made string and rope from the bark and the dark brown seed pods were turned into children’s toys. Protected by the pods are the seeds that are edible when roasted.
Professor gives microforests thumbs up
In an ABC article published in 2021, ANU Forestry Professor Peter Kanowski commented on the cooling potential of Canberra’s microforests. He said
“…. micro-forests had the potential to lower temperatures in urban parts of Canberra. I think we should expect to see more of these as part of the sort of diversity of ways that we add greenery to our cities, and that we use that greenery to deliver multiple benefits for the environment, but also for urban residents and communities,”
“I think the big picture is that we sort of need all hands on deck in our urban areas, because of the increasing average temperatures and the increasing frequency of heat waves.”He said as cities became more densely populated, they lost the benefits of backyard gardens on the urban temperature.
“But then, you know, there are little pockets of land in our densifying suburbs where micro-forests could be a great solution,” he said. One example, he said, could be putting a micro-forest to the west of a children’s playground, which could directly cool that space”.
Each year Professor Peter Kanowski schedules a visit to the Downer Microforest, to show his forestry students a Miyawaki style planting.
Best time to plant a tree
There’s a famous Chinese proverb that the best time to plant a tree was 20 years ago. The second-best time is now.
If you are curious about how to create a public microforest, The Climate Factory offers online learning and events. Robinson has made two home microforests and has created an instructional video based on her experience How to make a home microforest
This article was updated in February 2024.
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