Indigenous communities in Oaxaca, Mexico, have been working to restore the soil and forests, with remarkable success. Twenty-five communities have restored 49,000 acres (20,000 hectares) over the past 20 years. Restoration efforts are driven by the communities themselves, who together make up the Chocho-Mixtecas Community Alliance.
Before the Spanish arrived, the area supported a city of about 100,000 Mixtec. The current population of 2,800 struggles to find enough water to drink, let alone to grow crops. Large-scale goat ranching by the Spanish destroyed the soil. Goats pull plants up by the roots when they graze, so over-ranching with goats caused the land to erode all the way down to bedrock.
Rather than abandon their home, local communities decided to try to restore the soil. It's a long process. First, the bedrock must be broken up into small gravel that can hold water. Then trees that can survive in those conditions are planted. Eventually, the trees grow large enough to hold soil and protect native plants and animals.
It's a serious commitment of time, energy, and patience to see the process through. The ownership of the project by the entire community has ensured its success so far.
Under natural conditions, with no human assistance, it can take 500 years to create an inch of topsoil.
Over half of all habitable land on the planet is used for farming purposes. Almost 30% of this land is entirely barren for growing purposes, and is unable to contribute to our world’s growing demand for food. (Well Gardening, "Practicing Soil Restoration In Your Garden: 10 Actionable Tips")
Jeremy Williams has put together a booklet, "Soil", about soil degradation and restoration that you can read online or download.