Yep Sapwood – in opposite to the heartwood – is very sensitive. If seasoned too humid it will go moldy. If seasoned to warm and dry – like under the roof in a screed – it will overdry.

Today I prepered 4 yew staves that were gifted to me and it was unclear if they were seaasoned correctly. 2 of them showed good sapwood, 2 of them showed overdried sapwood. If the sapwood is overdried you cannot make a selfbow anymore because the back of the bow will break under the tension. Overdried Sapwood lost its tension strength. To still make good use of the staves and the precious heartwood you have the following options:

Back it with sinew, linnen or thick rawhide.

Back it with Bamboo or Wood-Backing (Hickory/Elm  etc.)
Make a heartwood only bow.

How do we recognize bad Sapwood?

By the color: Good sapwood is bright white / Bad Sapwood is brownisch-grey

By the feel under your drawknife: Good Sapwood cuts clean, tough and elastic / Overdried Sapwood feels crumbly and crispy unter the drawknife and splinters.

Sometimes – if you are lucky – only the top layers of the sapwood are degraded. So sometimes its enough to just remove the upper annual rings to find the good sapwood.