So I need a barren wasteland with some dead vegetation (mainly dead trees). There should be pretty much no living plants left but it should be apparent that it was a lush place for flora and fauna about 20-25 years ago.
What could have killed all the vegetation while leaving some dead trees still standing? What could be the reason for plants not growing back?
The thing that comes to mind is a volcanic eruption. But that usually brings nutrition to the area affected and that's why the place would probably be blossoming again after 20-25 years.
Could there be something in the ground like toxic soil or just low levels of nutrition that would make it inhabitable? What could the toxic soil be? How did it get there? Why would the ground suddenly lack in nutrition?
Any other reasons why this could happen?
There is no specific location for this wasteland, but I would rather not have it placed very far north or have it be a typical sand desert. It would take at least several days to walk through it. Assume Earth-like conditions and medieval tech.