Staves split from larger diameter trees seem not to do it as much. For one thing you can leave them more massive and dry them more slowly, and their own bulk resists some of the warpage. Obviously, they can twist and warp, but you ususally find out as soon as you split it if they are going to. It just seems saplings and branches WANT to go off in every direction.
I think it's because they are young and growing fairly dense wood very quickly, branching out, etc, so each year the tree is doing something different as it grows that year's ring. Like this year it grows a long branch at the top on one side, reaching for sunlight. But, last year this other tree had a large drooping branch leaning on it, and next year that tree will be dead and open up sunlight on that side, so the weight will shift, etc... reaction wood all over the place.
