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 Landscape Architect, Edwina Robinson 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 microforest 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 free resources to get you started.
Robinson has made two home microforests and created an online course and information guides to grow a microforest at home.
This article was updated in December 2024.