From the windswept Atlantic coast of Senegal to the shores of the Red Sea in Djibouti, the Great Green Wall initiative stretches for almost 8,000km across one of Africa's most extraordinary landscapes.
It crosses the Sahel - a vast, semi-arid band that separates the Sahara Desert from the greener savannahs further south. During the brief rainy season, grasses burst into life, seasonal wetlands fill and migratory birds arrive in their thousands. The Sahel supports more than 500 bird species and forms one of the world's most important migration corridors between Europe and Africa.
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Despite its name, however, the Great Green Wall isn't a giant line of trees marching across Africa. Instead, it has evolved into the world's largest landscape restoration programme, combining tree regeneration, healthier soils, improved water management and sustainable farming to restore degraded ecosystems across 11 countries.
Launched by the African Union in 2007, the initiative aims to restore 100 million hectares of degraded land by 2030, remove 250 million tonnes of carbon from the atmosphere and create 10 million green jobs.
"It's the biggest restoration programme in the world," says Tom Skirrow, chief executive of Tree Aid. "It's vitally important not just for the millions of people living across the Sahel, but more broadly for the world's ability to combat the climate crisis."
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For people living here, restoring the land isn't simply about conservation. Healthy soils produce better harvests, support livestock, retain scarce rainwater and help communities withstand increasingly frequent climate shocks.
Skirrow says the Great Green Wall has long been misunderstood.
"When it was first conceived, people imagined a physical wall of trees," he says. "But that was more of a storytelling narrative than what was actually required."
Instead, the project focuses on restoring entire landscapes. In some places that means planting native trees. Elsewhere it involves protecting woodland that is naturally regenerating, improving soil health, slowing water run-off after heavy rain and helping farmers adopt regenerative agricultural techniques.
Healthy soils are just as important as healthy forests. By increasing organic matter and improving water retention, degraded land can gradually recover, allowing native vegetation to return naturally while reducing erosion and making farms more resilient during drought.
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Although often overshadowed by Africa's famous safari destinations, the Sahel supports an astonishing diversity of wildlife. Towering ancient baobab trees punctuate the horizon, while umbrella thorn acacias and gum arabic trees provide food and shelter for wildlife including African bush elephants, critically endangered West African lions, Dorcas gazelles, patas monkeys and Nile monitors. Seasonal wetlands attract migratory birds such as garganeys, black-tailed godwits and Eurasian spoonbills, while residents including Abyssinian rollers, yellow-billed hornbills and colourful bee-eaters bring flashes of colour to the dry landscape.
As habitats recover, wildlife is beginning to respond. Working in Burkina Faso, Tree Aid has combined tree restoration with projects to improve soils and restore river systems.
"We've seen larger populations of elephants returning to that area than have been there for the last 30 or 40 years, according to the communities we've spoken to," says Tom Skirrow.
The return of elephants is particularly significant. As ecosystem engineers they disperse seeds over long distances and create natural clearings as they move through the landscape, helping to shape habitats that benefit countless other species.
Restoration doesn't just create habitats for wildlife. It also reduces pressure to clear remaining forests for agriculture, allowing both people and nature to thrive together.
The Great Green Wall is one of the world's most ambitious environmental projects but restoring such a vast landscape is far from straightforward. Funding remains one of the biggest hurdles. While billions have been pledged internationally, conservation organisations argue that too much money is slow to reach the communities carrying out restoration.
Political instability and conflict across parts of the Sahel have also slowed progress, while climate change itself continues to make restoration harder through hotter temperatures and increasingly unpredictable rainfall.
Monitoring success across thousands of kilometres presents another challenge, requiring governments, scientists and local communities to work together to understand which restoration techniques are having the greatest impact.
Rising temperatures, prolonged droughts, deforestation and unsustainable land use are degrading millions of hectares of land, threatening wildlife and the livelihoods of the communities that have depended on it for generations, are also other pressures.
Despite these challenges, the Great Green Wall has become one of the world's most significant symbols of ecological recovery.
It is already helping iconic species recover, from elephants and West African lions to migratory birds and vital pollinating insects, while improving food security, strengthening local economies and helping millions of people adapt to a changing climate. It also offers valuable lessons that could be applied to degraded landscapes around the world.
For Tom Skirrow, however, the true success of the Great Green Wall isn't measured in hectares restored or trees planted.
“It's the micro impact on one family or one community that really matters. If you can restore their landscape, you can see the differences immediately. You're talking one, two or three years and their lives are immeasurably better,” he explained.
The Great Green Wall may never resemble the uninterrupted barrier of trees its name suggests. Instead, it is becoming something far more remarkable: a living mosaic of recovering forests, flourishing wildlife and communities working together to restore one of Africa's most important landscapes.
