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Australia's tree (Acacia mearnsii) has across South Africa, taking over millions of hectares of land and pushing indigenous plants aside. Economist Saul Ngarava researches agriculture and the connection between , . He was part of a team who surveyed 1,184 homes in South Africa's North West, Northern Cape and Eastern Cape provinces, to see if those who burn black wattle for cooking have more energy security than those who don't. He also looked at whether there was potential for small businesses to cut down the invasive tree and make products from it. He talks to The Conversation Africa about his findings.

What is black wattle and what threat does it pose to the environment?

The black wattle is an invasive Australian tree that arrived in South Africa . It was originally introduced in plantations to create shade and windbreaks and to be used for wood fuels and fencing.

Some of the plantations were set up in the 1960s in the upper catchment of rivers. The trees' seeds blew into the rivers and were dispersed downstream, spreading the population. The black wattle population has now expanded over of land. It is spread along river channels and where there is a high water table.

Black wattle uses the amount of ground water compared to indigenous trees and negatively affects South Africa's .

It also damages South Africa's biodiversity. The tree grows faster than native vegetation and competes with indigenous plants for water and nutrients, crowding them out. This decline that eat indigenous vegetation. Growing in dense clumps, the black wattle trees are and create an increased fire risk.

What were the main drivers of the use of black wattle for energy?

compared 549 households in Matatiele (Eastern Cape) that used black wattle for household energy, with 556 households in Greater Taung (North West) and 79 in Magareng (Northern Cape) that did not. The purpose was to see if those who burnt black wattle for cooking had more energy security than those who didn't.

that high levels of unemployment and poverty levels had increased energy insecurity. This drove the use of black wattle as fuelwood.

For example, some of the households I surveyed had no income to buy electricity. The small amount of free electricity that South Africa provides to was not enough for them to survive on.

Some of the communities I studied were not connected to the national grid and couldn't buy electricity even if they wanted to. For example, a community in the Magareng municipality but without an electricity connection.

My research found that the black wattle offers a remedy to energy shortages when people live near large plantations. As it is an invasive species, there are already projects to eradicate it. For example, , a non-governmental organization in Matatiele, has raised funds to cut down the trees.

Through their , the organization gets young people to chop down the trees and turn them into products they can sell. Youth-led small businesses such as , and have established themselves based on the abundant black wattle trees.

How does using black wattle affect energy insecurity?

The study shows that because they cannot afford electricity or are not connected to the grid, rural South African communities usually generate energy from the resources available in their areas. This can include actively engaging in initiatives, or chopping invasive trees down as part of planned clearing, and using these as fuelwood.

However, the black wattle can be better used beyond fuelwood. Processing it into charcoal can improve its energy efficiency and also spark small charcoal businesses. South Africa does not have an official rural unemployment rate but joblessness is higher in rural areas, where there is no industry, than in urban centers.

, businesses and small industries from invasive species is essential in reducing poverty and establishing a in rural areas.

For example, black wattle wood can be turned into utensils, fencing and building materials, and sold.

Because these trees drain the levels, chopping them down will also improve the security of water supplies. Eliminating trees will also allow natural grasslands and thickets to regrow. These provide better grazing areas for livestock, and this improves food security in rural areas.

Burning wood carries health risks and increases greenhouse gas emissions. Why do you still recommend it?

Wood fuel and charcoal burning do cause greenhouse gas emissions and health risks. The solution to this is clean, renewable energy like solar or wind power. However, these types of energies are generally not available to rural communities of South Africa, because South Africa's rollout of renewable energy has to meet the growing need for energy.

This has also been worsened by a lack of energy infrastructure, population growth, inequalities and people being unable to afford energy.

The use of black wattle as an energy source is a convergence of factors: energy insecurity in the rural areas, and active projects that of black wattle due to its environmental impact.

My research argues that haphazard use of the black wattle as an energy source should be replaced by one where using the tree is carefully managed. Industries, jobs and businesses can add value to the invasive species.

This needs large scale investment from the government and private sector in projects. These projects must combine eradicating the wattle with reaching targets of increased biodiversity, and better water, food and energy security.

People in rural areas without any form of energy are already cooking on fire. So, converting the black wattle into charcoal would . Innovative cooking stoves such as the use less wood to cook, which means less exposure to smoke. This somewhat reduces the health risks.

Overall, the management of the black wattle aims to recover biodiversity and enhance water and food security. In the process, the by-product can be used as an energy source.

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