Land and soil
Topsoil
Topsoil is the upper layer of soil holding almost all of its organic matter, biology and available nutrients. It is where plants actually live. It forms over centuries and can be lost from a slope in a single monsoon once the cover holding it is gone.
Depth of topsoil is the most honest single measure of whether land is recovering, because it cannot be faked from the air and it cannot be produced quickly.
It is also the part of restoration that a photograph cannot show, which is why soil depth is measured and reported alongside canopy.