We had entered the forests to the east of Ascension in order to attempt to determine the reason that the Elven nations of the forest had cut off communication with the city.
We were attacked by forest creatures (Dryads and Woads I believe) who claimed that a corruption was defiling the forest and that we were such defilers. Unfortunately, we were forced to battle them.
After subduing the creatures, we continued and came across a large path where necrotically infested Grubs had cut a path through the woods. Clearly THIS was the actual source of the corruption.
We followed the path and after helping a Mother (again in her Primal form) worshipping goblin tribe cleanse a spiritual site of the necrotic corruption, we reached the central holy site of the elven nation.
Here it became clear where the Necrotic energy was coming from. During the undead war that initiated our travel to Furlough in the first place, the elven nation sent an army to Ascension to aid their allies. This army was led by Queen Vereeni. She was who we encountered at the glen. She had died at Ascension. It would appear that the release of the Lich Queen had also released (or reanimated) an undead Vereeni.
Unfortunately, she had enchanted much of the fey court (including her own husband) and we were forced to fight them with only the aid of an ancient elvish druid who had merged with an oak tree (another primal worshipper of the Mother).
Dispatching this threat, we followed a trail of corrupted trees back to Mount Ascension. It appears that Vereeni was using her innate ability to move from tree to tree to return to her territory. It would appear that our actions on Mount Ascension are linked to her reappearance, though I can not yet determine the exact causal relationship.