Climate ready trees in tiny forests

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.

Young leaves of a Kurrajong in the Downer tiny forest in Canberra.

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.

These Kurrajongs are planted at
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