I’ve worked up stocks from walnut before. I wanted a tree about 18” in diameter at a minimum. Slabs are sawn @ 3” in thickness to accommodate a cheekpiece if desired. About 2 1/2” if you don’t want a cheekpiece. The best figure in a walnut tree is in the taproot (stump figure) and the crotch where larger limbs branch off the main trunk ( crotch or feather crotch figure). It goes without saying, when I take a walnut tree, I bring a shovel and backhoe. The worst mistake you could make was to cut off at ground level. You’re leaving the best wood in the ground. We’d dig up the stump section, fell the tree and only then measure off eight or more feet in length before cutting. I’d sometimes get with the sawmill ahead of time and ask them what length they wanted the logs. I only dug up walnuts that were in the woods, never a yard tree, as the mill wouldn’t take it. The usual and customary length of time to cure was one year per inch of thickness of the slabs. Standard drying techniques were used. Inside a barn out of the rain, inch spacers between stacked slabs, ends of the slabs painted or paraffin sealed to prevent splitting.
All that being said, birch may or may not be any different from what I just said…..I’m sure there are more experts on here that can weigh in.
The best figure is often in the stump as you pointed out, but it is the buttresses leading down the trunk and out into the flat root portion of the root where the best blanks live. The actual tap root is usually quite vertical in walnuts and tapers quickly.
