Sometimes at small scale, and sometimes at very large scale. Often even just leaving it alone, and putting a stop to the practices that destroyed the land, (e.g. keeping the grazers out) sometimes is all that is needed. For example, a simple fence can allow vegetation to re-establish itself without getting destroyed by hungry deer, sheep, or whatever.
Once you have plants with deep roots, the land gets better at retaining water and soil stops eroding away. Once the land can retain water, a lot of life can make use of that. Nature tends to be resilient and adaptable. There are no one size fits all solutions for every landscape. But there are a lot of things that have been tried that have yielded good results.
In any case, stuff like this is not as surprising as it seems. Organic matter rots. That usually involves a lot of bacteria and insects. The result is basically compost. A giant heap of compost and a lot of wild seeds from neighboring grounds with a bit of water is one hell of a good way to kickstart nature. Probably the best decision was to leave it alone.