Earlier quoted context omitted.
Sheep. They’ve tried and sheep tend to eat all the saplings. Unlike in other places the sheep are not penned in, they’re free to roam which means any area you want to try and re-forest in a fairly hostile environment to begin with has to be expensively fenced off until they get to a fairly good size.
Can’t fence in the sheep? Fence in the trees.
Or bring in wolves.
The shepherds farm the sheep, it might be an idea to ask them to stop it.