"By omitting the impact of charcoal production in forest cover change, current assessments may be missing a highly significant component of land cover change in Africa," Fernando Sedano of the University of Maryland, US, told environmentalresearchweb. "Based on urbanization and energy projections, the importance of this driver of land cover change is likely to increase, together with its importance in the livelihood and adaptation capabilities of rural communities. We need to understand the drivers of forest degradation and develop the tools to successfully monitor them over time."

Nearly 80% of the population in African urban centres use charcoal as their main source of energy for cooking. And Africa’s urban population is set to rise from 30% of the total in 2000 to 60% by 2050. "Charcoal is and will remain the main energy source for cooking in African cities," said Sedano. "The energy demand of the cities will result in more pressure on the forest resources of the continent."

Forest degradation often doesn’t show up in satellite images as well as deforestation does because it’s on too fine a scale. So Sedano and colleagues looked at very high-resolution data from commercial satellites for Tete province in central Mozambique from 2008–2014. They focused on the main charcoal production areas – the districts of Changara and Moatize.

"We found that very high-resolution images would allow us to identify charcoal kilns and, analyzing images from several years, we could learn where, when and how much charcoal was being produced," said Sedano. "Still, satellite images could not tell us the whole story. To have an idea of how many trees, how much biomass and carbon was consumed in charcoal production, we had to combine satellite information with the biophysical parameters collected in the field."

In situ, the researchers assessed how much forest had been cut down around each kiln and the kiln’s charcoal output. Charcoal producers generally remove trees with a trunk diameter of more than 15 cm, leaving at least 10% of the canopy cover.

The team also estimated the above ground biomass removal from the number of kilns and the average amount of charcoal produced per kiln, as well as converting this to carbon emissions. Combining the urban population and its charcoal use provided another assessment of the annual above ground biomass removal.

"This work aims to improve the current understanding of forest degradation in tropical dry forests of southern Africa as a first step to develop a forest degradation monitoring system, contributing to a growing body of research that investigates the link between urban energy consumption and forest degradation," writes the team in Environmental Research Letters (ERL) .

In total, the team identified 8561 kilns in satellite images captured from 2011–2014. Initially most charcoal production was in the district of Changara but the focus moved to Moatize in later years. Over time the kilns tended to move away from paved roads and the city of Tete. The extent of charcoal production areas also increased.

Over the same time period, the study indicates that around 95,000 tonnes of biomass was removed by charcoal production, leading to nearly 37,000 tonnes of carbon dioxide emissions. The charcoal demand of Tete led to roughly 65 square km of degraded forest, the team estimates. By 2040, this figure could rise to between 89 and 212 square km.

"Our analyses show that forest degradation can be more significant than previously anticipated and that in some areas can have a larger impact on forest cover than deforestation," said Sedano.

Sedano reckons that forest degradation due to charcoal production could be prevalent in other areas of southern Africa. He and his colleagues plan to test whether the same degradation patterns occur in other parts of the Miombo region. "To do so, we will first improve our image processing techniques so that we can operationally detect charcoal kilns in large datasets of very high-resolution satellite images," said Sedano. "Then we will extend our analyses to other major charcoal production areas. A final goal will be including the impact of forest degradation and carbon emissions associated with charcoal production in regional assessments for southern Africa."

Sedano and colleagues reported their findings in Environmental Research Letters (ERL) .

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