Your backyard can make a difference

During the ‘angriest summer on record’, that of 2019–2020, greater Sydney recorded its highest ever temperature of 48.9°C.

This extreme is a peak event that sits atop a broader picture of underlying temperature increases as a result of human-induced climate change. Outlier heat events such as these are perhaps the most dangerous direct manifestation of climate change on human health as they are predicted to become more frequent as global temperatures rise by 1.5°C or more.

As global citizens we can all play our part in moving away from fossil fuel combustion by switching to renewable energy, growing some of our own food and being conscious of waste. But as gardeners, we can deepen our contribution using the power of plants to drawdown carbon dioxide. After all it was the unique ability of plants to convert sunshine, water and carbon dioxide into sugars that created fossil fuels in the first place.

Carboniferous vs Anthropocene

About 300 million years ago during the ‘Carboniferous’ period, the Earth was tipped into a global cooling phase that was driven by the incredible growth of giant plants such as ferns and club mosses (some of which grew to 40m tall), which had a voracious appetite for carbon dioxide. This spectacular plant growth led to great volumes of dead plant material buried under anaerobic swamps where microbes could not reach them.

These deposits became fossilised into the fuels that we have dug up and burnt to drive industrialisation. While the Earth was naturally sequestering away millions of tons of carbon on the back of plant activity, polar ice caps grew and global temperatures plummeted.

Today, in order to reverse the warming we are causing, we need to stop burning ancient plant deposits (fossil fuels) and plant as many carbon-capturing trees, shrubs and other plants as we can in order to harness the power of photosynthesis to bring temperatures down. This is the challenge of the ‘Anthropocene’, the current geological epoch characterised by human impact on global ecosystems.

Bringing the global back to the local

Whilst the challenge of global warming is huge and on a planetary scale, the heatwaves of our daily lives are far more tangible. But here too gardeners have an opportunity to harness the ability of plants to make our lives better. Australia is one of the most urbanised countries in the world with more than 80% of us living in, or attached to, our cities. This presents us with a wonderful opportunity to use plants to make some quick changes to our living environments and can help to alleviate some of the temperature extremes of summer.

A recent study1 of the heat mitigation contribution of backyards in western Adelaide found that private spaces offer significant untapped opportunities for urban greening and cooling, particularly in suburbs with low vegetation cover. It was found that private gardens contributed significantly to reducing land surface temperatures in urban areas with temperatures 5–6°C lower where gardens were planted.

Local governments are very active in planning and planting the ‘urban forest’. As an example, the City of Melbourne, who manage in excess of 80,000 trees on public land, has a target of doubling this number by 2040. Gardeners can augment this public planting within our own gardens to complete the picture, linking up our gardens with public plantings to create a true urban oasis.

If all urbanites were gardeners

I like to wander suburban streets and imagine what they would look like if all the people suddenly had to move away and their gardens, the street plantings and public spaces were left to their own devices. I imagine that with time the trees would begin to grow and spread such that the canopy would begin to close, shrubs and perennials would colonise the gaps and a pioneer ecosystem would begin to develop. I envision a bird’s eye view of the suburbs with leaf canopy dominating rooves and paving, and where green dominates the scene.

I like to wander suburban streets and imagine what they would look like if all the people suddenly had to move away and their gardens, the street plantings and public spaces were left to their own devices. I imagine that with time the trees would begin to grow and spread such that the canopy would begin to close, shrubs and perennials would colonise the gaps and a pioneer ecosystem would begin to develop. I envision a bird’s eye view of the suburbs with leaf canopy dominating rooves and paving, and where green dominates the scene.

Proverbially we think of the ‘leafy’ suburbs as the affluent ones but this doesn’t have to be the case. If we start to place a higher priority on the place of plants in our everyday lives, we could all live in cool urban forests.