DRESSED in a faded T-shirt bearing the face of the American rapper 50 Cent, Samson Okenye leans on a shovel in Nyakweri forest in south-western Kenya. A 62-year-old from the Rift Valley, he has a new gig for his retirement. Having worked in a factory for most of his life, he is now chopping down trees and burning them for charcoal. He sells each bag he produces from his crude earthen kilns for 400 Kenyan shillings (about $4). Men carry it off on motorbikes to Nairobi, the capital, and Kisumu, Kenya’s third-largest city.

Charcoal is one of the biggest informal businesses in Africa. It is the fuel of choice for the continent’s fast-growing urban poor, who, in the absence of electricity or gas, use it to cook and heat water. According to the UN, Africa accounted for three-fifths of the world’s production in 2012—and this is the only region where the business is growing. It is, however, a slow-burning environmental disaster.

In Nyakweri, the trees are ancient and rare. Samwel Naikada, a local activist, points at a blackened stump in a clearing cut by burners. It is perhaps 400 years old, he says. The effect of burning trees spreads far. During the dry season, the forest is a refuge for amorous elephants who come in from the plains nearby to breed. The trees store water, which is useful in such a parched region. It not only keeps the Mara river flowing—a draw for the tourists who provide most of the county government’s revenue. It also allows the Masai people to graze their cows and grow crops. “You cannot separate the Masai Mara and this forest,” says Mr Naikada.

Short-term financial interests are doing just that. Most of the burners are not from nearby, where people are mostly Masai. Instead, like Mr Okenye, they come from farther north-west. At the moment the forest is communally owned, but local power-brokers illegally sell parcels of it to the burners. “The problem is the need for quick money,” says Johnson Mopel of the Transmara Wildlife Scouts Association, a local NGO. “Charcoals are like hot cakes in the marketplace.”

Nyakweri is hardly the only forest at risk. The Mau forest, Kenya’s largest, which lies farther north in the Rift Valley, has also been hit by illegal logging. Protests against charcoal traders broke out earlier this year, after rivers that usually flow throughout the dry season started to run dry. In late February a trader’s car was reportedly burned in Mwingi, in central Kenya, by a group of youngsters who demanded to see the trader’s permits. At the end of February the government announced an emergency 90-day ban on all logging, driving up retail prices of charcoal by 500%, to as much as 5,000 shillings a bag in some cities.

The problems caused by the charcoal trade have spread beyond Kenya. In southern Somalia, al-Shabab, a jihadist group, funds itself partly through the taxes it levies on the sale of charcoal (sometimes with the help of Kenyan soldiers, who take bribes for allowing the shipments out of a Somali port that Kenya controls). The logging also adds to desertification, which, in turn, causes conflict across the Sahel, an arid belt below the Sahara. It forces nomadic herders to range farther south with their animals, where they often clash with farmers over the most fertile land.

In the power vacuum of the eastern Democratic Republic of Congo, rampant charcoal logging has destroyed huge swathes of Virunga National Park. That threatens the rare gorillas which tourists currently pay as much as $400 a day to view, even as it fuels the conflict.

In theory, charcoal burning need not be so destructive. In Kenya the burners are meant to get a licence. To do so, they have to show they are replacing the trees they are cutting down and that they are using modern kilns that convert the trees efficiently into fuel. But, admits Clement Ngoriareng, an official at the Kenya Forest Service (KFS), the rules are laxly enforced. Some suspect that powerful politicians stymie efforts to police burners.

In Nyakweri forest, trade has slowed since logging was banned in February. But Mr Naikada does not think the prohibition will change much. In 2015, after environmentalists kicked up a fuss in the Kenyan press about the loss of Nyakweri, a KFS camp was set up to protect the forest from loggers. A helicopter buzzed over the trees, putting out fires. Yet by the end of 2016, after the forest service’s budget was cut, the camp had closed. As the dry season gives way to rains, protests will die down and the new ban will probably be lifted. And then the logging will start again.