Well yes and no. If the soil's been sterilised the entire thing needs to be rebuilt from the grasses upwards, forests don't spring up out of nowhere they build up from precursors.
Thanks, I was imagining the smaller stuff as being part of the forest but I suppose maybe the plants that arise first don’t necessarily stick around for the entirety of the forest lifecycle?
Exactly. I don’t remember the exact cycle but basically you first get grass type colonisers, then you might get shrubs, then possibly trees densifying to a forest. Even the tree presence would change as the forest builds up as some essences don’t like being crowded (so won’t replace themselves once the forest densifies) while others prefer shade (so won’t appear until there’s a canopy proper).
It is called "secondary succession" (primary being colonisation from scratch on bare rock)
Perhaps a new forest, but plants in general (current conditions may favor grassland, or something else). It's "re" because there was an ecosystem there before, and now it's returning. Contrast with, say, a brand new island that is the result of volcanic action. Then it'd be just plain old colonization by way of wind-blown seeds, or seeds that survived a bird's digestive tract.