If Australia wants to stay cool, it should stop land clearances and plant some trees

Koala bears are among the cuter victims of land clearances. Image: Getty.

Land clearance is on the rise in Australian states like Queensland and New South Wales, with land clearing laws being fiercely debated.

In Queensland in 2013–14, 278,000 hectares of native vegetation were cleared: an area 1.2 times the size of the Australian Capital Territory. A further 296,000ha were cleared in 2014–15. These are the highest rates of deforestation in the developed world.

Land clearing on this scale is bad for a whole host of reasons. But our research shows that it is also likely to make parts of Australia warmer and drier, adding to the effects of climate change.

How do trees change the climate?

Land clearing releases greenhouse gases into the atmosphere, but the effect of land clearing on climate goes well beyond carbon emissions. It causes warming locally, regionally and even globally, and it changes rainfall by altering the circulation of heat and moisture.

Trees evaporate more water than any other vegetation type – up to 10 times more than crops and pastures. This is because trees have root systems that can access moisture deep within the soil. Crops and pastures have 70 per cent of their roots in the top 30cm of the soil, while trees and other woody plants have 43 per cent of their roots in the deeper part of the soil.

The increased evaporation and rough surface of trees creates moist, turbulent layers in the lower atmosphere. This reduces temperatures and contributes to cloud formation and increased rainfall. The increased rainfall then provides more moisture to soils and vegetation.

The clearing of deep-rooted native vegetation for shallow-rooted crops and pastures diminishes this process, resulting in a warmer and drier climate.

We can see this process at work along the “bunny fence” in southwest Western Australia, where there is a moister atmosphere and more clouds over native vegetation compared with nearby farming areas during summer.

The rabbit-proof fence, which keeps pests from the rest of Australia out of the Western Australian pastoral lands. Image: Rougengineer/Wikimedia Commons.

Studies in Amazonia also indicate that, as deforestation expands, rainfall declines. A tipping point may be reached when deforestation reaches 30-50 per cent, after which rainfall is substantially reduced. Complete deforestation results in the greatest decline in rainfall.

More trees, cooler moister climate

We wanted to know how land clearing could affect Australia’s climate in the future. We did this by modelling two scenarios for different amounts of land clearing, using models developed by CSIRO.

In the first scenario, crops and pasture expand in the semi-arid regions of eastern and southwest Australia. The second scenario limits crops and pastures to highly productive lands, and partially restores less productive lands to savanna woodlands.


We found that restoring trees to parts of Australia would reduce surface temperatures by up to 1.6℃, especially in western Queensland and NSW.

We also found that more trees reduced the overall climate-induced warming from 4.1℃ to 3.2℃ between 2050 and 2100.

Replanting trees could increase summer rainfall by 10 per cent overall, and by up to 15.2 per cent in the southwest. We found soil moisture would increase by around 20 per cent in replanted regions.

Our study doesn’t mean replanting all farmed land with trees: just areas that are less productive and less cost-effective to farm intensively. In our scenario, the areas that are restored in western Queensland and NSW would need a tree density of around 40 per cent, which would allow a grassy understorey to be maintained. This would allow some production to continue such as cattle grazing at lower numbers or carbon farming.

Political and social challenges

Limiting land clearing represents a major challenge for Australia’s policymakers and farming communities. The growing pressure to clear reflects a narrow economic focus on achieving short- to medium-term returns by expanding agriculture to meet the growing global demand for food and fibre.

However, temperatures are already increasing, and rainfall is decreasing over large areas of eastern and southwest Australia. Tree clearing coupled with climate change will make growing crops and raising livestock even harder.

Balancing farming with managing climate change would give land owners on marginal land new options for income generation, while the most efficient agricultural land would remain in production. This would need a combination of regulation and long-term financial incentives.

The climate benefits of limiting land clearing must play a bigger part in land management as Australia’s climate becomes hotter and drier. Remnant vegetation needs to be conserved and extensive areas of regrowth must be allowed to regenerate.

And where regeneration is not possible, we’ll have to plant large numbers of trees.The Conversation

Clive McAlpine is a professor, Leonie Seabrook a landscape ecologist and Jozef Syktus a principal research fellow in the Global Change Institute at the The University of Queensland.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

Covid-19 is highlighting cities' unequal access to green space

In the UK, Londoners are most likely to rely on their local park for green space, and have the best access to parks. (Leon Neal/Getty Images)

As coronavirus lockdowns ease, people are flooding back to parks – but not everyone has easy access to green space in their city.

Statistics from Google show that park attendance in countries across the globe has shot up as people have been allowed to move around their cities again.

This is especially true in urban areas, where densely populated neighbourhoods limit the size of private green space – meaning residents have to go to the park to get in touch with nature. Readers from England can use our interactive tool below to find out how much green space people have access to in their area, and how it compares to the rest of the country.

 

Prime Minister Boris Johnson’s announcement Monday that people are allowed to mingle in parks and gardens with groups of up to six people was partially following what people were doing already.

Data from mobile phones show people have been returning to parks across the UK, and also across Europe, as weather improves and lockdown eases.

People have been returning to parks across the world

Stay-at-home requirements were eased in Italy on 4 May, which led to a flood of people returning to parks.

France eased restrictions on 1 May, and the UK eased up slightly on 13 May, allowing people to sit down in public places so long as they remain socially distanced.

Other countries have seen park attendance rise without major easing of lockdown – including Canada, Spain, and the US (although states there have individual rules and some have eased restrictions).

In some countries, people never really stopped going to parks.

Authorities in the Netherlands and Germany were not as strict as other countries about their citizens visiting local parks during lockdown, while Sweden has famously been avoiding placing many restrictions on people’s daily lives.


There is a growing body of evidence to suggest that access to green space has major benefits for public health.

A recent study by researchers at the University of Exeter found that spending time in the garden is linked to similar benefits for health and wellbeing as living in wealthy areas.

People with access to a private garden also had higher psychological wellbeing, and those with an outdoor space such as a yard were more likely to meet physical activity guidelines than those without access to outdoor space. 

Separate UK research has found that living with a regular view of a green space provides health benefits worth £300 per person per year.

Access is not shared equally, however, which has important implications for equality under lockdown, and the spread of disease.

Statistics from the UK show that one in eight households has no garden, making access to parks more important.

There is a geographic inequality here. Londoners, who have the least access to private gardens, are most likely to rely on their local park for green space, and have the best access to parks. 

However the high population in the capital means that on the whole, green space per person is lower – an issue for people living in densely populated cities everywhere.

There is also an occupational inequality.

Those on low pay – including in what are statistically classed as “semi-skilled” and “unskilled” manual occupations, casual workers and those who are unemployed – are almost three times as likely as those in managerial, administrative, professional occupations to be without a garden, meaning they rely more heavily on their local park.

Britain’s parks and fields are also at significant risk of development, according to new research by the Fields in Trust charity, which shows the number of people living further than a 10-minute walk from a public park rising by 5% over the next five years. That loss of green spaces is likely to impact disadvantaged communities the most, the researchers say.

This is borne out by looking at the parts of the country that have private gardens.

The least deprived areas have the largest gardens

Though the relationship is not crystal clear, it shows at the top end: Those living in the least deprived areas have the largest private green space.

Although the risk of catching coronavirus is lower outdoors, spending time in parks among other people is undoubtedly more risky when it comes to transmitting or catching the virus than spending time in your own outdoor space. 

Access to green space is therefore another example – along with the ability to work from home and death rates – of how the burden of the pandemic has not been equally shouldered by all.

Michael Goodier is a data reporter at New Statesman Media Group, and Josh Rayman is a graphics and data visualisation developer at New Statesman Media Group.