Could any of you kind folks tell me how to progress past the protective barrier in the underground grove, or is this the end of the current build?
Either way, very impressed thus far Zion, keep up the good work.
You need to do the witch quest and have either the hunters or the witch on your side. They will remove the barrier.
To start the quest, talk to the guy in black on the Bloody Jaw Tribe. He's basically right at the center of the tribe.
He'll give access to the ruins where the witch is (close to your tribe, to the left).
However I highly recommend you waiting for the full chapter 3. Chapter 3 right now is barebones, nothing more than a demo.
Many new things will be added to it.