brocpuff responds:
Hickory is harder than maple.
Birch shouldn't be harder than hickory, but it sounded like the OP was working some kind of pecan, instead of true hickory: both are Carya, but the true hickories (shagbark, shellbark, mockernut, pignut) are considerably harder with shagbark and shellbark the hardest.
Pretty, though. Sharp tools help a lot.
Charlie Self
"Don't hit at all if it is honorably possible to avoid hitting; but never hit soft." Theodore Roosevelt