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.

 
 
 
 

How spurious imperial science affected the layout of African cities

Freetown, Sierra Leone. Image: David Hond/Freetown From The Air/Wikimedia Commons.

As the European powers spread across the world, systematically colonising it as they went, one of the deadliest enemies they faced was disease. In 1850s India, one in twenty British soldiers were dying from such diseases – on a par with British Empire casualty rates during World War II.

When Europeans started dropping dead the minute they got off the boat, the scientists of the day rushed to provide their own, at times fairly dodgy, solutions. This era coincided with a key period of city planning in the African colonies – meaning that there is still visible evidence of this shoddy science in the cityscape of many modern African cities.
For a long time altitude was considered a protection against disease, on the grounds that it was far from the lowland heat associated with putrefaction. British officials in India retreated to the ‘hill stations’ during the warm season; this practice continued in the African colonies established by all sorts of European powers in the late 19th century.

So it was that one bunch of imperialists established the capital of German Kamerun at Buea, high on the side of Mount Cameroon. The city still has a population of 90,000 today. Evidence of this height fetish can still be found in the ‘Plateau’ districts of Brazzaville, Dakar and Abidjan as well as the ‘Ridge’ district of Accra.


Malaria, particularly, was an ever present fear in the colonies, and it did much to shape the colonial cities. It’s a sign of the extent to which 19th century medical science misunderstood how the disease was spread that its name comes from the French for ‘bad air’. By the late 19th century, knowledge had managed to progress far enough to identify mosquitoes as the culprits – but views still wildly diverged about the appropriate response.

One solution popular in many empires was segregation. The Europeans had incorrectly identified Africans as the main carriers of the disease; African children under five were believed to be the main source of malaria so they were to be kept far away from the colonists at all times.

And so, many powers decided that the European settlers should be housed in their own separate areas. (Of course, this wrong headed but at least rational response wasn’t the whole explanation: often, sanitary concerns were used to veil simple racial chauvinism.)

The affluent Hill Station – a name reminiscent of the Indian colonies – in Freetown, Sierra Leone was built as a segregated suburb so Europeans could keep well clear of the local children. Today, it’s where the home of the president can be found. Yet despite all this expensive shuffling of Freetown’s urban landscape, inhabitants of Hill Station came down with malaria at about the same as those who lived elsewhere.

 

The Uganda Golf Course, Kampala. Image: Google Maps.

In Kampala, Uganga, a golf course now occupies the land designated by the British powers to protect the European neighbourhood from the African. A similar appropriation can be seen in Kinshasa, Democratic Republic of The Congo, where a zoo, botanical garden and another golf course can be found the land earmarked for protecting colonial officials and their families.

All this urban juggling was the privilege of immensely powerful colonial officials, backed up by the military might of the imperial powers. The indigenous peoples could do little but watch as their cities were bulldozed and rebuilt based on the whims of the day. Yet the scars are still visible in the fabric of many modern African cities today.