Originally I set out to map all the rotting stump locations for Ugdenbloom between Coven's Refuge and Barrowholm and ended up adding other points of interest that might be worth checking out.
Ugdenbog POI Map
These are all the rotting stump locations that I've found so far, as well as notable spawn locations for the Beast nemesis and Bargoll. The Yoknar bounty is a Barrowholm bounty and the Ollivioth and Yuvolloth spawns require you to have the quest or finished the quest from Barrowholm so those require you to have sided with Barrowholm.
Note the Wendigo Altar in lower Ugdenbog does not spawn 100%, I'm not sure if there is another location for it to spawn or not.