BBC – Future – How do weeds help combat climate change?



More than 60 years ago, when he was a child, farmer Peter Andrews saw his first dust storm. He still remembers it. "The noise was horrible," he says. "We hid in the house waiting for it to happen. The whole sky was dark. And the damage we saw the next day was even more terrible. "

The wind had uprooted many of the trees on his family's property completely naked. Some of his horses and cattle suffocated, unable to breathe in the dust.

That early experience led him to a particular call: try to regenerate the land of Australia, since dust storms occur in warm, arid regions where there is little vegetation to anchor the soil.

"It really took me … to think about how to find solutions to keep the earth in balance," says Andrews. "For many decades I learned from observation how to keep the land fertile, how each landscape has its own natural system. Here in Australia, we have devastated the landscape with European-style agriculture. We have to find a way to regenerate the earth. "

In the 70s and 80s, Andrews became interested in sustainable agriculture. He looked at the water courses and the plants that grew on his property and tried to avoid fertilizers and herbicides. I wanted the farm to be as weather-resistant as possible.

A major problem was the drought. Another was that the weeds grew on the property, while the native plants were not.

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He had two great achievements. First, plants are essential to keep the earth in balance. Second, so is water.

He saw that each landscape has its own contours: a point where water originates and a point towards which it flows. To explain an eroded landscape, you start at the highest point, decrease the speed of the water flow and then work downward, filtering the water with whatever vegetation there is, he explains. This was the genesis of his idea of ​​natural sequence agriculture.

Weeds for water

Climate change and land cleansing have spurred rising temperatures and extreme weather events in Australia

It has been the driest and hottest year recorded in most of Australia. A recent scientific report describes how last summer in Australia was characterized by "prolonged heat waves across the continent and unprecedented hot days, wildfires across Australia and heavy rains and floods in northern Queensland." Climate change and land cleansing have driven increased temperatures and extreme weather events in Australia, according to the report, and "the last four years have been the four hottest years recorded for the global surface temperature" . Many people, unable to grow or feed cattle or sheep, are abandoning their farms as a result.

Research by the Nature Conservation Council (NCC) of Australia also warns of deforestation in Australia, especially in New South Wales "on a scale that we have not seen in more than 20 years," says the executive director of NCC, Kate Smolski.

The NNC report explains that digging forests mean there are fewer trees to "produce rain, cool the climate and store carbon."

Andrews calls Australia "the laboratory for the world when it comes to adapting to climate", due to this intense climate, and the worsening climate, conditions and deforestation.

The natural sequence of agriculture has four main elements. First, restore fertility to improve the soil; second, increase the groundwater; third, re-establish the vegetation, even with weeds if necessary; Fourth, understand the unique needs of a particular landscape.

Andrews' ideas are not universally accepted. For decades, many saw him as a nonconformist. He is not a scientist, and it was not until 2013 that scientific evidence proved that natural sequence agriculture can be effective.

Some critics question whether better land management and avoidance of destructive farming methods (such as cutting trees) would, in the first place, require the need for a natural-sequence agriculture. Others do not agree with their suggestion to use weeds: conservation projects generally promote the planting of endemic Australian plants, instead of allowing invasive weeds to grow, as they are believed to compete with native plants for scarce water.

But a natural sequence cultivation pilot site, located an hour's drive east of Canberra, seems to be showing that Andrews' ideas on weeds can work, even if only on a small scale so far. The pilot site is a 6 km stretch of Mulloon Creek, which traverses a network of organic farms that now use and promote Andrews' work.

The Sustainable Development Solutions Network of the United Nations announced in 2016 that the Mulloon Creek Natural Farms are one of the few agricultural sites in the world that are truly sustainable

The United Nations Sustainable Development Solutions Network announced in 2016 that the Mulloon Creek Natural Farms are one of the few agricultural sites in the world that are truly sustainable, and praised the model of natural sequence agriculture.

At Mulloon Creek, I meet with Gary Nairn, president of the Mulloon Institute, a research and teaching organization for regenerative and sustainable agriculture that promotes Andrews' work. He points out the invasive blackberries that his team reduced; The cut and cut shrubs are now blocking part of a pond, helping to filter it. The sound of running water and small birds fill the air when I approach.

The Mulloon Institute, which is based on a barn next to a pond named after Andrews, teaches natural sequence cultivation methods to farmers, scientists and university students. The Mulloon Institute is also working with several Australian universities to monitor water along the stream, made with piezometers (water measuring equipment) installed by scientists from the Australian National University and the University of Canberra.

"Scientists have shown that natural sequence agriculture increases the flow of water, raising the water table," explains Nairn.

His team is now working on another 43 km of creek that travels 20,000 ha of farmland to build more weedy dumps, like a wall of a dam, through the stream. The dams are made of stones; The cracks between the stones are filled with chopped blackberry to filter and slow down the flow of the river.

Despite so little rain, the stream is now running again and the pastures that were once arid, eroded by the drought, are turning green. This is because landfills are working, allowing the soil to absorb more moisture, which allows plants to grow along the edges.

"Weeds and landfills draw energy from the water and rehydrate the landscape," says Nairn.

The whole process is a bit like creating "giant sponges with weeds," he says.

What we have learned is never to take out a weed until you know what purpose that weed was for – Gary Nairn

"What we have learned is never to take out a weed until you know what purpose that weed met. A large amount of weeds generally means that there is something wrong with the fertility of the earth. If you extract it, you must replace it with another plant, "he says.

But these weeds can be cut and placed in a stream, like in the pond outside the Mulloon Institute.

According to Nairn, in this way, Australian native plants will grow back slowly. In fact, some are already doing it along the creek.

Carbon sink

The beauty of weeds is that they also act as a carbon sink: a system that removes carbon from the atmosphere and stores it in another form of storage. These can help control climate change.

"Forests, oceans and soils can remove carbon dioxide from the atmosphere and store it," says Christa Anderson, climate researcher at the World Wildlife Fund in the United States.

Anderson explains that the amount of carbon dioxide that an ecosystem can absorb depends on where it is located and how it is managed.

There is a lot of agricultural practices that can also increase carbon storage – Christa Anderson

"While forests have the greatest potential for additional carbon storage and can therefore help mitigate the emission of carbon dioxide and other greenhouse gases, there is also a lot of agricultural practices that can also increase the carbon storage, "says Anderson.

"We need to remove carbon from the atmosphere by improving forest management, protecting and restoring wetlands, peat bogs and seagrbades, and improving our agriculture."

Some scientists now wonder if even small projects like Mulloon Creek could function as a carbon sink to restore habitats, if enough famers also make "giant weed sponges".

"When it retains water in the landscape, it also returns carbon to the landscape and makes it more productive and sustainable," adds Nairn.

This is important because so much forest is being cleared for large-scale agriculture that carbon sinks are being lost. The northern fringes of New South Wales and Queensland have become arid since the clearing of land for mbadive farms. But, gigatonne for gigatonne, soils and plants contain twice as much carbon as the atmosphere, so more plants are needed, not less, to absorb the increase in carbon production from the burning of fossil fuels.

The question is whether smaller projects like this one will be enough to bring farms back to life, given the enormous rates of deforestation and soil degradation.

Nairn believes there are reasons for optimism. "You just need the will to do it," he says. "What makes us proud is to give young people hope with natural sequence agriculture, we hope that they can still live on the land if they manage water and plants better."

Peter Andrews agrees, although he adds that he always disliked the term natural sequence agriculture.

"The name bothers me, it's really looking at the landscape and returning it to what it used to be, to its best capacity, every plant has a purpose."

As world leaders debate whether, when and how carbon emissions should be reduced, a sustainable farm in Mulloon Creek in Australia is demonstrating that low-tech weeds can help reduce carbon and make a river run again. It is a small but significant solution to a serious global problem.

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