Explainer: Armillaria ostoyae first parisitises trees and after they die (or are killed) then it shifts to a saprophytic mode to decompose the tree.

My summary after wondering why you chose the word "consume".

https://en.wikipedia.org/wiki/Armillaria_ostoyae

  rivals the aspen grove "Pando" as the known organism with the highest living biomass and perhaps rivalled by a colony of Posidonia australis on the Australian seabed that measures 200 square kilometres (edited)