The Rahim River basin in the Rahim Wastes is filled with the papyrus plant, which the Rahim centaurs use to make papyrus (the writing surface). They've been making it for centuries, but trade has only relatively recently opened with the desert folk, so papyrus has just started making its way to the rest of Morgrave in the last hundred years. Papyrus is a cheap alternative to vellum, but doesn't last as long - it's found its niche in the market, but some still prefer the old way for their writing.
Impact in Rahim
Adventurers and traders have only been coming to the Rahim Wastes for about a hundred years. Once they made contact with the centaurs, there were only a few trade goods that that the centaurs produced that the traders wanted: varanuses, salt, and papyrus. Varanuses are too rare for the centaurs to trade freely, and salt isn't mined heavily, but papyrus is something that can be mass produced and has a decent demand.
Papyrus is the single trade good that the centaurs produce that can get them a decent stream of income, allowing them to purchase goods from the outside world. Although the Rahim River basin is fertile and allows a lot of crops, the import of more food has allowed the centaur tribes in the desert to expand beyond their previous capacities.
Impact in the Rest of Morgrave
Papyrus has begun to displace vellum as the main material for writing in Morgrave. Overall, this has little effect on the world, but it did coincide well with the golden age in Hymbra, which suddenly started needing more writing materials for their scholarly studies, including the study of arcane magic and the creation of spellbooks. Papyrus doesn't last as long as vellum, but it is cheaper and makes smaller and lighter books.