Cities should just add a deforestation/nature tax to new lots. The market will only have lots that already has a property on it.

It is important for older cities to rejuvenate and when cheaper alternatives don't exist, they will be forced to redevelop. See how large cities redevelop in constrained areas.

A land value tax might be a more effective way to encourage redevelopment. That way it doesn't matter if unused land is in public or private hands.