If number of poisonous vines + companions reaches companion limit or wolf limit, Summon Wolf ability is replaced by Howl ability and you cannot summon more wolves until vines expire.
It’s almost like vines are counted as companions, however you can still summon other companions when vines are up. For example if I have 1 wolf and 6 vines, I can still summon raptor but not another wolf.
Vines can be summoned e.g. with Fury Leap or Eterra’s Path unique boots.
Video: