Creating Canberra’s micro-forests

In 2019 Australia sweltered through its hottest and driest year on record. The year culminated in the Black Summer bushfires that destroyed millions of hectares of vegetation, killed people and animals and destroyed livelihoods.

During that year I set up the social enterprise, The Climate Factory. The goal was to build climate-cooling native micro-forests in Canberra’s urban parks. That year Canberra received only 358mm of rain (58% of its annual average).

Heatwaves will be more common in the future and impact the most vulnerable in our society. And heatwaves kill more people in Australia than any other natural disaster.

The defining experiences

Two experiences influenced my journey through 2019. The first was stumbling across the work of Shubhendu Sharma from Afforestt. He was making tiny forests across the world – I realised I’d found my calling.

The second was a visit to Australia’s National Botanic Garden on a hot January arvo. There I discovered the air temperature at the bottom of the constructed rainforest gully was 11°C cooler than the bitumen carpark. Using a combination of vegetation layers, building soil organics and applying water, the rainforest gully was acting like nature’s evaporative cooler. See more at afforestt.com

Downer micro-forest; a pilot project In 2020, I built Canberra’s first native micro-forest (or tiny forest) in a public park in Downer. While I was influenced by Afforestt’s method of dense planting, I didn’t follow it strictly. Sharma adheres to the Miyawaki method, which involves using species that occur in a local forest, dense planting and organic soil preparation. Many of Canberra’s forest communities are dominated by eucalyptus. Given the recent Black Summer bushfires, I thought recommending a gum grove underplanted with a range of vegetation layers would alarm residents.

For the Downer micro-forest I chose species from the hotter, drier climates that Canberra was likely to experience in the future. In 2017, The Australian National University School of Forestry conducted desktop research on ‘climate ready’ trees for Canberra. They found the Kurrajong (Brachychiton populneus) was the number one tree for a hotter, drier future.

At Downer, we planted Kurrajong, White Cedar (Melia azedarach), Casuarina cunninghamiana (number 2 on the ANU’s list), Allocasuarina, Tuckeroo (Cupaniopsis anacaroides) as a test and Queensland Bottle Tree (Brachychiton rupestris). The wattles (Acacia dealbata), a pioneer species, have grown rapidly. They quickly create a dense thicket, like you find in a post-fire landscape.

They protect other species, add nitrogen and organics to the soil, and will die out over time. Under the canopy are a range of native species, from ground covers, grasses and shrubs to forbs and climbers.

Climate modelling shows by 2090 Canberra’s future could potentially be 4°C hotter with 29% less rainfall, so I worked with water harvesting designer Paul Totterdell to incorporate 800mm deep trenches and a bog within the micro-forest. This means rainwater falling on the site is diverted towards plant roots, rather than at the soil surface.

Since building the Downer micro-forest we’ve created another micro-forest and nature play space led by the community at Watson. As well as using many of the same tree species, plus five small mallee (Eucalyptus mooreii), we introduced deciduous exotic trees to allow winter sun to play areas. A grove of five deciduous Crepe Myrtles (Lagerstroemia ‘Natchez’) were planted around the recycled timber boardwalk and shop front.

Some trees are better evaporative coolers than others

Not all trees use water equally. From a water conservation point of view, low water use plants are often favoured. However, this is missing the bigger picture. In a hotter future we will need trees that keep us cool.

Research by Associate Professor of Urban Studies, University of Western Sydney, Sebastian Pfautsch found in one school playground over 2019–20, Queensland Brushbox (Lophostemon confertus) consumed an average of 156 litres of water per day versus Banksia integrifolia, a meagre 9 litres per day. Through evapotranspiration, water is released from a tree’s leaves and takes latent heat with it, cooling the air.

Moruya home micro-forest

In 2016, I started to make a home micro-forest in Moruya inspired by local sand dune communities. I used the local coastal wattle (Acacia longifolia) as fast growing pioneer plants. Trees include Swamp Oak (Casuarina glauca), Allocasuarina and self-sown Silky Oak (Grevillea robusta). Once I’d established dense cover I added some trees from dry rainforest regions, like Illawarra Flame Tree (Brachychiton acerifolius), Queensland Lacebark (Brachychiton discolor) and macadamia.

In five years I’ve created a 90m2 slice of bushy privacy. Our micro-forest cools our home from western sun and winds, and creates habitat for native bees, blue tongue lizards and birds.

Planting trees for the future

Tree planting is something we can all do, whether in a pot that you take with you when you move or as a legacy tree for the future.