At Widou, in the middle of the Ferlo region of northern Senegal, there will be no rain till the end of July. At this difficult time of the year most of the zebu, sheep and goats have moved south in search of pasture under the watchful eye of their Peul herdsmen.

The life of the village and the dozens of surrounding hamlets is marked by regular convoys that stop at the well and fill their makeshift tanks. But several hundred metres away, in an open-air laboratory, another story is struggling to make its mark.

In the nursery built by the Senegalese Water and Forestry Agency (OEF) men carrying watering cans are hard at work. Women, bent over rows of little plastic containers, are potting seedlings, ready to be planted at the first sign of rainfall. This year some 390,000 such seedlings will be needed, for Widou is one of the first communities selected by the government to roll out the great green wall (GGW) programme, a pan-African scheme initiated by the African Union in 2007. To halt the advancing desert, it aims to plant a 15 kilometre-wide swath of trees stretching 7,600km across the continent from Dakar to Djibouti. Eleven countries are taking part but Senegal, with 533km of wall on its territory, is the first where the project is really taking shape.

Colonel Matar Cissé, an OEF engineer, readily acknowledges that "The great green wall is a crazy project". But he dismisses the idea that the aim is to build an impenetrable barrier 15km wide. "It would make no sense," he says. "It would be more accurate to say we are going to build up the forest cover wherever possible, build reservoirs, set aside nature reserves for large mammals, which have almost completely disappeared, while making allowance for the main routes used by the herds." The idea is nevertheless useful, because it reflects a positive attitude showing that "we have chosen to colonise the desert, rather than letting it have its way".

At the head of the Senegal GGW agency, Cissé is tasked with turning this dream into reality. "We will succeed. We have recruited top scientists and we have a fair bit of experience too," he says. Since 2008 reforestation has advanced by about 5,000 hectares a year.

With each campaign the agronomists, botanists and soil specialists have improved their technique. They started by selecting appropriate species. Seven were chosen for their ability to adapt to the harsh conditions, but also the services they offer the local community: Acacia senegal, a form of gum arabic, Balanites aegyptiaca for its berries and the oil that can be extracted from the stones, Ziziphus for its fruit. "We have to plant species which offer no incentive for logging," says Aliou Guissé, Professor of Plant Ecology at Cheikh Anta Diop University in Dakar (UCAD). They also have to increase the distance between trees to limit competition between plants. "The soil structure here is in a very poor state, so for reforestation to work, it has to be reconstituted with more intensive bacterial activity. It's one of the project's main constraints. We will have to wait seven or eight years to know whether this has worked out," says René Bally, at France's Science Research Centre.

The green wall is certainly a technical challenge, but above all it raises human issues. "This project will only succeed if we can convince people it can raise their living standards," Guissé warns. It will soon be up to local people to ensure the green wall puts down long-term roots. The same is true of the seven-hectare market garden on the road out of Widou where 300 women produce tomatoes, lettuce, melons, potatoes and such.

"In three years' time we should be self-sufficient and we're already preparing for that moment," says Fatou Aïdara, the head of the market gardening committee. She has always lived here, enduring the great droughts of the 1970-80s when people and livestock died. She has also seen the unfounded hopes raised by development schemes hatched by international cooperation. This time, she believes, the promises may come true.

This story originally appeared in Le Monde