User blog comment:IceFireWarden0/Next Official Elder Scroll's Game Predictions/@comment-4043978-20121130003728

The Hist trees have been extinct since the last known sample was taken during the questline of the Fighter's Guild, when the Hero of Kvatch overtook the Blackthorn faction that wanted to harvest the tree's sap for bad purposes. The Hero had to destroy the tree to save the sample, and theresult was basic extinction.