For the Wood Elves, simply having the tree may be enough, and Take Root is frankly not such a bad negatrait! He has his value maximized just sitting on the LOS and giving a guard assist to the two poor line elves next to him

With this in mind, I wanted to propose three Take Root changes aimed at the Halfling team. If the changes are too much for the Wood Elf team, I'd suggest removing the treeman from the Wood Elves altogether, or having a different negatrait for the Woody tree.
Option 1- Take Root simply removed from the 'Fling trees.
Option 2- Take Root changed to GFI requires a 4+ always.
Option 3- Take Root same as now, but MA is reduced to 1 for the rest of the drive, and can not GFI... all of this is after failing the 2+ roll, of course.