> A forest turns solar energy into wood, locking up that energy in an inedible form. Grass, on the other hand, can be eaten by grazing animals and turned into meat. If you're living off the land but not farming, then you'd prefer it to be covered in grass instead of trees.

Hem, not. This is not how it works. A very old, well cared apple tree can produce 800 Kg of apples a year. You can't breed a cow just using the grass growing in the same surface. It needs more space. A lot of animals eat leaves, twigs, fruits, and flowers of trees. The thicker the "layer alive" that can sustain animals the better. Trees are like the fat of the land. Rocky areas are like the skeleton of the land. Grasslands left unregulated enter very fast into a tragedy of the commons spiral by being invaded by cattle, sheeps and goats turning into rocky areas.