Investigate the Strange Object next to the Broken Corpse to determine what might have befallen the Cenarion Thicket. Then return to Earthbinder Tavgren just outside the thicket in Terokkar Forest.
I have no idea what killed all of the druids here. I've been away for a couple of days on a survey of the Bone Wastes to the south.
Please, you must help me to uncover what's behind this horrible tragedy. Go into the thicket and look for a clue that might reveal something to us. When I was in there briefly, I could have sworn I saw a dead Broken and a strange object next to him.
And don't worry about Treelos - he might have been driven insane by what happened, but I think he's mostly harmless.