Francophile jellies: why is the Upper Berry region (Haut Berry) of France called the "strong country" (Pays Fort)?

It’s a reference to the hard soil found there.

Here is an explanation in French in about the fourth paragraph. It says that the Pays Fort in Haut Berry gets its name from the strength of the arable soil and that the verdant and lush scenery is refreshing to the eye of the visitor after the bareness of the Champagne region.

So, @janbb, is there also a “pays faible”? Is there also a Bas Berry?

(The book that you referenced talks of a “pays perdu”.)

Thank you, and @thorninmud, for your replies!