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.

 
 
 
 

On Walter Benjamin, and the “Arcades Project”

Passage Verdue, Paris. Image: LPLT/Wikimedia Commons.

In 1940 a small group of refugees were turned away at the French-Spanish border. Having fled the Nazi invasion of France, they hoped to find safety in Spain. One of their number, a German-Jewish philosopher and writer, intended to have travelled onwards to America, where he would certainly be safe. So distraught was he by the refusal he met at the border that he took his own life.

The writer in question was Walter Benjamin, the prominent critical theorist who has contributed so much to our understanding of urban society, and he died with a manuscript close at hand. When asked previously if the briefcase of notes was really necessary to a man fleeing for his life he had replied, “I cannot risk losing it. It must be saved. It is more important than I am.”

The work that Benjamin died protecting was the Arcades Project. It was to be his magnus opus, intended by the author to illuminate the contradictions of modern city life. But it was never finished.

To Benjamin, the subject of the work, the arcades of Paris, were relics of a past social order, where consumerism ruled. The arcades were a precursor to the modern mall, lined with all sorts of shops, cafes and other establishments where visitors could buy into the good life. The area between these two lines of businesses was covered with glass and metal roofs, much like a conservatory: it gave visitors the high street feel in an intimate, sheltered and well-lit setting. You can still find examples of such places in modern London in the Burlington and Piccadilly arcades, both off Piccadilly.

Such arcades proved hugely popular, spreading across Europe’s capitals as the 19th century progressed. By Benjamin’s time, though, his type of shopping area was losing custom to the fancy department stores, and in Paris many of them had been obliterated in Haussmann’s city reforms of the 1850s and ‘60s. Whereas Parisians could once visit 300 arcades, now only 30 remain.

Through his research Benjamin started to see the arcades as representative of a pivotal moment in social history: the point when society became focused on consumption over production. Buying the latest fad product was just an opium, he thought, dulling senses to the true nature of the world. By bringing light to this, he hoped to wake people up from the consumerism of the 19th Century and bring forth some kind of socialist utopia.


He also warned that this shiny veneer of progress was hiding the true state of things. Instead, he revered crusty old cities like contemporary Marseilles and Moscow, where social life was more honest. In this way, Benjamin contributed to the intellectual movement focused on stripping away the excess of revivalism, standing alongside architects such as Le Corbusier. 

Through his newspaper essays throughout the first half of the 20th Century, Benjamin also became one of the first thinkers to focus on urban isolation. His suggestion that we can be most alone when among such a dense mass of other people is something many in modern cities would sympathise with. His work wasn’t all doom and gloom, however, as he saw cities as our salvation, too: laboratories from where society’s problems can be worked out.

It was 2000 before an English translation of the unfinished the Arcades Project was published, but by then the work had already had a significant impact. Just as he stood on the shoulders of giants such as Baudelaire and the Surrealists, modern thinkers have drawn on his work. Benjamin's concerns about common architectural forms can be seen to inspire modern architects such as Laurie Hawkinson, Steven Holl, Tod Williams and Billie Tsien.

The city of Paris itself was as much a part of the Arcade Project’s inspiration for Benjamin as was his intellectual predecessors. In his letters he repeats that it felt “more like home” than Berlin, and his days were spent marvelling at how the old and the modern exist together on the Parisian streets.

How groundbreaking the Arcades Project really was is hard to say. The fact it wasn’t finished certainly scuppered Benjamin’s plans to wake society up from its consumerist slumber, but that doesn’t make the work inconsequential. His fairytale of steel and glass is as much about the relationship between its author and Paris as it is a theoretical work. By putting the city as the main subject in human’s social history he laid the groundwork for future generations of thinkers.

Benjamin was lost to the tragic tide of the 20th century history, and his death marked the end of the project which could have changed the way we think of the urban landscape. Even if you shy away from the grandiose or don’t buy into his promises of socialist utopia, reading the work can still offer some eclectic factoids about 19th century France. At any rate, it must be acknowledged that the man gave his life to the betterment of society and the cities in which we live.