Slash-and-burn helps forest biodiversity

 SLASH-AND-burn agricultural practices, banned by governments because of the risk of uncontrolled fires, provide better growing conditions for valuable new trees than more modern methods of forest clearance, a study suggests. Starting in 1996, researchers cleared 24 half-hectare areas of tropical forest in Quintana Roo state, in southern Mexico, using three methods: clear-felling, where most of the trees are cut down; bulldozing; and slash-and-burn, a practice  common among smallholders, in which trees are felled, left to dry and then burned, to prepare the land for agriculture. Mahogany seeds and seedlings were then planted and, after 11 years, the researchers compared the sites and found that slash-and-burn techniques had provided the best growing conditions for mahogany. But, more interestingly, many valuable species had thrived in the slash-and-burn plots, said Laura Snook, one of the study authors and programme director at Bioversity International, which conducts research into agricultural biodiversity for the improvement of livelihoods. In clear-felled areas, more than half of each area contained tree species of no commercial value, Snook said. In areas cleared by slash-and-burn, 60 per cent of species were commercially valuable. Additionally, the largest trees in slash-and-burn areas were 10 per cent bigger than those in bulldozed areas. Snook was presenting the results of the study — which ended last year — at the annual conference of the International Society of Tropical Foresters, at Yale University, US, in January. In clear-felled plots, trees grow from trunks, and roots remain in the ground, which creates a canopy favouring shade-loving trees. These tend to have no commercial timber value. “Many valuable timber trees require sunlight to regenerate,” said Snook. She added: “The stimulus to growth [in slash-and-burn plots] is a result of the burning, which releases the nutrients in the trees that were felled, dried and burned, and makes them available to new trees”. Slash-and-burn is also cheaper than modern clearing methods and more familiar to local people. But some governments have banned this practice because of uncontrolled fires. “Policymakers may not be aware that fire is a natural phenomenon in many forests and is important to sustain the diversity,” Snook said. Fabian Islas Gutiérrez, director of the country’s National Centre for Disciplinary Research in Conservation and Improvement of Forest Ecosystems (CENID-COMEF), welcomed the research and said that the study is the first of its kind to be conducted in Mexican forests. “We have verified that, after a disturbance such a hurricane or a strong fire, vegetation is able to re-establish. In that sense, there is consistency with Snook’s results.” But he added the method may not be viable in different conditions from those in which the experiment was conducted. (SciDev)

 Sail-inspired turbine for cheaper wind energy

 A TUNISIAN invention that harvests wind energy through a design inspired by sailboats promises cheaper, more efficient energy. The bladeless wind turbine, the Saphonian, named after the wind divinity that was worshipped by the ancient Carthaginians, also promises to be more environmentally friendly than existing wind turbines that produce noise and kill birds through their blade rotation. Instead of rotating blades, the Saphonian’s sail-shaped body collects the kinetic energy of the wind, Anis Aouini, the Saphonian’s inventor, said. He explained that the resulting mechanical energy moves pistons which generate hydraulic pressure that can be stored in a hydraulic accumulator or converted into electricity. “This is not the first bladeless wind turbine, but we thought outside the box: the initial idea came from sails — the only human system that can capture and convert the bulk of the wind’s power into mechanical energy,” said Aouini. An average wind turbine captures only 30 to 40 per cent of the wind’s kinetic energy, while the Saphonian can capture up to 80 per cent, according to Aouini. Hassine Labaied, chief executive of Saphon Energy, the start-up energy company established to get the turbine to market, said the Saphonian reduces the aerodynamic and mechanical energy losses associated with rotating-blade turbines. “Our second generation prototype is 2.3 times more efficient, and costs nearly half the price of its predecessors [conventional wind turbines]. It discards the most expensive components in a traditional wind turbine, which are the blades, hub and gearbox,” said Labaied. Aouini and Labaied patented the technology in Tunisia in September 2010, and received an international patent in March 2012. Saphon Energy is now looking for a partnership with a manufacturer to deploy the technology worldwide. “We are negotiating with a number of international companies that produce renewable energy technology, and will finalise this by the end of this year,” said Labaied. He estimated that it would take up to two years until the commercial product reaches the market. Ali Kanzari, a renewable energy expert and director-general of Solar Energy Systems, said that the Saphonian “seems to be a radical and economically viable alternative to bladed turbines”. However, he added that “the manufacturing step is important as it will determine how the market will accept it”. “The electricity produced through wind in Tunisia represents five per cent of total electricity production in the country,” Ayadi Ben Aissa, former chief executive of the Tunisian Society of Electricity and Gas (STEG), said. He said that using the Saphonian technology could produce up to 20 per cent of Tunisia’s electricity from wind in the medium term. (SciDev)

 Rising emissions may double sweet potato size

 RISING LEVELS of carbon dioxide (CO2) in the atmosphere caused by human-driven emissions might lead to larger sweet potatoes, a staple food for many African and Asian countries, research reveals.

     Sweet potatoes could double in size with the increase in CO2 levels currently forecasted for the end of this century, according to research by a team from the University of Hawaii, United States. The team presented their finding at a meeting of the American Geophysical Union, in San Francisco this month (3-7 December).

      The researchers grew a white-fleshed sweet potato variety from Hawaii in two types of fertiliser at current CO2 levels of 352 parts per million (ppm), as well as in three raised CO2 environments: 763, 1,108 and 1,515 ppm.

     According to the Intergovernmental Panel on Climate Change, atmospheric CO2 levels will be between 500 and 1,000 ppm by the year 2100.

     Even at 763 ppm of CO2, the tubers grew up to 96 per cent larger.

     “It is more than likely that we will be reaching much higher CO2 levels than previously expected and it is therefore important to understand how plants will respond to elevated CO2 at much higher concentrations,” Ben Czeck, one of the researchers, tells SciDev.Net.

     In addition, he says that climate change is expected to do the most harm to developing countries that rely heavily on root crops such as sweet potato.

     The researchers now want to find out if growing larger sweet potatoes will have any negative impact on their nutritional content, Czeck says.

     Previous studies revealed that the protein content in wheat, rice, barley and potatoes dropped by 15 per cent when grown under CO2 levels double those of today. The drop is caused by a series of impacts on plant physiology stemming from the higher levels of the gas.

     “The nutritional contents we are looking at are calories, dietary fibre, protein, sugars and micro- and macro-minerals,” Czeck says.

     Orange- and purple-fleshed varieties of sweet potato are rich in beta-carotene, which the body converts to vitamin A. They are being grown to try to reduce child malnutrition in African countries.

     Gabriela Burgos, who leads the Quality and Nutrition Lab at the International Potato Center (CIP), in Peru, says it is vital to study how raised CO2 levels will affect root and tuber crops, because much of the world’s population depends on them for food.

     “At CIP, we are trying to add more nutritional content to potato and sweet potato varieties, but if in a few years those varieties are going to be oversize, their nutritional content could be diluted,” she says. So it is good to have some way of dealing with the anticipated changes, she adds.

     But Wolfang Gruneberg, CIP geneticist and sweet potato breeder, thinks the real problem will not be higher atmospheric CO2 levels but the effect of raised temperatures on plants.

     “Plants use water to cool down. There are many places in the tropical world with drought. So the problem is not going to be the carbon dioxide but the [extra] heat that it would generate,” he says.

     CIP is evaluating the temperature range that sweet potatoes can withstand. As part of this, Gruneberg is planting a number of sweet potato varieties from CIP’s genebank — the most complete of the world — in the hottest areas in north Peru. (SciDev)