This may be a tangential issue, but using the Taiga as a sample is a bit of a misnomer. This is not a predominately agricultural region of Elyria. You may want to re-figure your calculations for a more Agri-based environment.
If I read the tribal lore correctly, the Brudvir don't do a lot of farming for just that reason. It just isn't sustainable. They get most of their dietary needs from a protein based diet. They hunt it. And supplement it with found foodstuffs such as those that will grow in this non-agricultural area.
This then requires them to interact with the other tribes, in particular the Hrothi and the Neran, to obtain the majority of their agricultural based items. I suspect a fairly brisk trade system will have to exist for them to survive and prosper. I'm picturing something similar to the early American west where the voyagers/mountain men would exchange pelts and furs yearly for provisions at some type of Rendezvous.
I think that many of the tribes in the more extreme biomes are designed that way so that the Neran and T'oresk become the intermediary trade tribes necessary to hold the continent together and promote interaction vs. retreating to isolation and xenophobia. For the Brudvir it is about agriculture. For the Janoan it is about labor. And so on.