Currently our characters can split boards of a trunk preferably with Splitting axe or Woods man’s axe. But any metal axe will do the job.
Another historical method to split boards, is with hard wood wedges.
So I suggest to allow splitting boards with ‘wooden wedge’*1, made from either slender trunks or from stakes. Maybe 4-6 wedges from a stake, bunch more from slender trunk. The wedges should be “scrap” or 0 squirrel hides value. Fire hardening requirement debatable?
Actual trunk splitting to boards with wedges should be slower than with axes, but also yield higher quality boards, so give a ~10% skill bonus. With ~30min time penalty or same time as non-preferred axe. If using wedges, blunt weapon, as with final step in tanning, should be required to drive in the wedges.
And last, not least, the board splitting should be pausable task.
*1 the wedges could be also required in deconstruction of log walls, especially if working alone without companion(s)