They brought in 500 tortoises to slow the Sahara’s advance in 2021: five years later, the success of the ‘system engineers’ arrived

In the Sahel, daytime temperatures can climb as high as 140°F, while nighttime brings a sharp drop in temperature. On this hardened landscape, rainwater struggles to penetrate the ground. Moisture evaporates almost immediately, leaving seeds unable to germinate.

For that reason, a group of researchers released 500 African tortoises into a barren region on the southern edge of the Sahara. The animals belong to the species Centrochelys sulcata, which evolved to thrive under exactly these conditions. Five years later, images of the area have revealed the appearance of green patches across the landscape.

How do tortoises make a difference?

The African spurred tortoise is the largest mainland tortoise in the world and the third-largest tortoise species overall, behind only the Galápagos and Aldabra giant tortoises. Adult males can weigh more than 220 pounds. Beyond its impressive size, the species is particularly notable for its digging ability.

To escape extreme heat, these tortoises excavate burrows reaching depths of 30 to 50 feet. The tunnels provide shelter from scorching daytime temperatures and chilly desert nights while also helping aerate the soil.

When these burrows break through the hard crust that forms on the ground, rainwater is able to seep into the soil rather than running off the surface. As a result, the land retains moisture more effectively, allowing water to remain available for longer after rainfall.

Senegalese success

This effect has already been documented in Senegal. Since 1992, the organization S.O.S. (Save Our Sulcata) has operated breeding and reintroduction programs for the species. A 2020 report by the International Union for Conservation of Nature (IUCN) highlights the Village des Tortues sanctuary in Noflaye, home to more than 300 tortoises and the source of multiple reintroductions into the animals’ native habitat.

The tortoises’ burrow entrances, and the surrounding disturbed soil, create a more stable microclimate. While the animals do not intentionally disperse seeds, those already present in the soil, or carried in by the wind, can germinate thanks to the increased moisture and protection found around the burrow system.

The effect extends beyond plant life. These conditions attract insects and microorganisms, helping revive activity beneath the surface. Over time, vegetation becomes denser around the burrows, creating green patches that are visible even in satellite imagery and are closely linked to the tortoises’ digging activity.

The release of roughly 500 tortoises in 2021 drew significant attention, although IUCN data show that Senegal’s reintroduction program has been underway for decades. Monitoring of established groups has recorded survival rates above 80% over multiple years, a crucial factor in maintaining both the animals’ burrowing activity and their long-term impact on the landscape.

No reforestation techniques or soil treatments were used. The intervention consisted simply of reintroducing a native species whose numbers had been reduced by hunting, agriculture, and livestock grazing. Over time, areas that were once barren began to recover vegetation and attract wildlife, including birds and small vertebrates, leading to a broader increase in biodiversity.

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