The fifteen nascent soul realm elders were certainly not expecting such a change to happen in the Millennium forest.
The humans powers living around the millennium forest did know that the forest had some sources of spirit Qi in it. But due to the threat of the beasts, they never deemed it worth to enter the innermost area.
It was after all, known that the sixth ring where the rulers of the forest lived was the source of the spirit Qi. The few that had visited it had said that while it was better than the normal spirit Qi density of air, with the threat of the beasts and the harsh condition, it was not worth heading there.
Besides, the millennium forest brought them more resources in other forms such as beast materials and spirit herbs. So destroying the forest for the spirit Qi rich area wasn't much of a viable option anyway.
But now… now they were blown away.