From the rules it seems that the Take Root roll should really be done at the very start of an action (before a player takes an action), and therefore before the Stand Up roll (which would be the first roll of the actual declared action):
(Emphasis is my addition)
From Take Root rule:
From Prone Player rule:Before taking any action roll a d6. On a 2 or more, the player may take his action as normal. On a 1, the player "takes root," and his MA is considered 0 until a drive ends, or he is knocked down.
While prone the player loses his tackle zone and may do nothing except stand up at a cost of three squares of movement when he takes his next action.
So in this case, it has been pointed out that if dice are rolled in this order, it is not possible for a prone treeman to take root? But surely being prone is not meant as a way to avoid making your Big Guy negatrait roll? Or does he have to make the Take Root roll while prone, and if he fails cannot stand? Or does the pass/failure of a Take Root roll while prone allow him to attempt to stand as normal, but simply root him once he's up?*
*In which case the game mechanic of allowing him to Stand Up before making his Take Root roll is still possibly slightly incorrect, but completely irrelevant. It only says make the Take Root roll before taking an action, not before declaring it (i.e. no waiting to see if you pass Take Root before declaring if he will just Move or Blitz)