There is a wall appearing across the African continent, dividing north and south. But this wall isn’t to keep migrants out, or to keep smuggled goods in check. It is holding back sand. The scheme is helping to contribute to a far more ambitious project known as the Great Green Wall. It is attempting to grow an 8,000km (4,970 miles) barrier across the entire width of Africa to hold back the spread of the Sahara desert. While the desert waxes and wanes with the drought that comes with the changing seasons, declining rainfall combined with deforestation and soil degradation has seen it grow.

Over the past century, the Sahara desert has been expanding by more than 7,600sq km a year and is now 10% larger than it was in 1920. The creep has been particularly pronounced to the south, where it has spread into the Sahel by more than 554,000sq km over the same period. The desert now covers an area of 9.4 million sq km (3.6 million sq miles).

You have to watch where you step in Paga, on the very edge of northern Ghana. Wander into the wrong part of this dusty African border town and you may just come face to face with the toothy grin belonging to one of the resident crocodile population.

The local people here have cultivated an alarmingly close relationship with these powerful reptiles, which live in “sacred” ponds around the town. According to local legend, the first chief of Paga was saved by a crocodile while on a hunting expedition and he decreed that none of his people would harm the animals from that day forward.

Today the locals still care for the crocodiles, feeding and protecting them. Women can apparently wash their clothes in the ponds without fear and some brave souls even swim with the animals. Tourists, drawn by the promise of “friendly” crocodiles, are encouraged to pose for gawky photographs while touching the reptiles. They are safe to approach, apparently, provided you do so from behind. But Paga, and its crocodiles, face an encroaching threat from the land around it. Positioned on the southern edge of the semi-arid Sahel region that stretches across the African continent, Paga’s surrounding area is covered with a delicate, sandy soil that clings precariously to the landscape. Twisted trees and stunted shrubs, perfectly adapted to coping with the periods of drought that hit the area, help to hold the soil together.

But pressure from the growing population in Paga and the surrounding villages has led to many trees being cleared to provide fuel and building materials, and to make way for farmland. Without these to hold the soil together, wind and heavy rainstorms simply sweep it away, leaving nothing for crops and the wild vegetation to put its roots into. The land is turning into a desert.

“There is a lot of degradation in our environment because there's a lot of deforestation,” says Julius Awaregya, founder of a local environmental group in Paga. “It has serious implications for our future generations, so we need to conserve what we have.”

Awaregya is now helping to coordinate efforts to keep the desert at bay by building, of all things, a wall. But this is no ordinary wall, made of brick, stone or concrete. It is instead formed from trunks, branches and leaves – a living, green barrier to hold back the near lifeless desert.

On the day we speak, Awaregya had already dispatched members of his team to three nearby villages with truckloads of seedlings so they could join groups from the local community to plant new trees. Today they are planting acacia, mahogany, neem and, most importantly, baobab.

Fully grown baobab trees are a sight to behold. Their thick bulbous trunks, topped with a punk-rock bristle of stumpy limbs pointing skyward, have an other-worldly appearance. Baobabs – which are actually succulents – are perfectly adapted to the tough, dry conditions of the savannah and can live to be over 2,000 years old.

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