Borderlands

A land where mundane meets the supernatural, giving birth to people who could make the impossible possible.

A thin border between the lands of God and the Chaos-infected Forbidden Forest. That is how priests describe it, at least. For most of them the Borderlands are just as bad as the Forbidden Forest itself, and anyone who would wish to go there a potential heretic. Or worse yet, a foul sourcerer. As you can imagine, this kind of bias did not do much for the region's reputation.
Then again, it is hard not to see the point. The Borderlands are very dangerous and very sparsely populated, two things that probably have a lot to do with each other. So much that centuries ago the whole region was bestowed by the Ardenian emperor to his Kimnan subjects, as only people adventurous enough to actually want the place. They are still the ones running the place, eventually turning into an independent collection of local communities rather than a part of any large nation. Which, if I may point it out, is rather unusual for Ordonia.

Ecosystem

The only predictable thing about this place is that nothing really is.

Just like the Forbidden Forest, the Borderlands near it are bountiful in both plants and animal life. And much more easily exploitable by the local population, by the way. In fact, I have seen references that this area was once considered a part of the Forbidden Forest until part of it was cleared up and deemed safe enough for human life. Just enough to find people crazy enough to stay there of their own free will.
However, as with the Endless Forest the local ecosystem is constantly changing. New lifeforms come out of the forest all the time, changing all that the locals have gone accustomed to over the past years. This happens often enough that most scholarly books are outdated by the time they are written, which makes any degree of scientific debate rather difficult. That is why you are only getting vague descriptions from me here.

History

So why does everyone still tolerate the Borderlands? Why not raze them down, lock the entire area in a series of fort and forbid anyone from venturing in there? The Ardenian Empire ruled those lands for centuries, after all. And a number of emperors tried to do just that, sinking endless resources and manpower into the project - and failling every time. That land could not be tamed, at least not by force.
And just as importantly, as we looked across the oceans the human civilisation has gradually came to rely on some of the products coming out of the Forbidden Forest. Which most of the time means coming out of the Borderlands. Two chief examples are the Instant Clay and the Dry Water, both crucial to our ability to supply ships on long voyages. If Kimnans want that land for some reason, it turned out to be both easier and cheaper to just let them have the whole lot and buy whatever we need without any of the risk.