I need to take a better look at Barebones, but probably? I wouldn’t say that FtB and Cairn 2e are incompatible per se, but FtB was written when the worldbuilding in Cairn was much more implicit, and it doesn’t take advantage of a lot of the procedures that have been added since. It’s probably best to think of FtB as a forestcrawl for Cairn, similar (but not congruent) to the forestcrawl procedures outline in the 2e Warden’s Guide.