Those cracks are drying checks, caused by the wood drying too fast on the outside, while the inner wood is still wet. The shrinking surface wood has no place to go, so it's tears apart.
There are two things you can do: First, reduce it to near finished bow dimensions. The thinner the wood, the less drying forces can build up, because there is simply less wood to build up these forces. Second, move the wood to a place so it dries slower. That will cause less of a difference between the moisture content of the inner and the outer wood. Find a place that is colder and/or more humid and/or has less air movement (wind). An RH of 25% is really low. If that is as moist as you can find in your house, try to move the wood outside the house (cellar, garage, shed etc.). If that is not possible, wrap the stave in something that will slow the release of moisture to the air. Wrap it in news paper (plastic is too moisture resistant for my liking and tends to keep in all moisture, which is undesirable and may cause fungus). Or coat the entire surface in shellac.
I still think it is not hickory, because I don't see a ring porous wood in the pictures. It has every appearance of a diffuse porous wood (such as maple). If you can make a clear close-up picture of the wood and show the (ring) porous character of the wood, I'll stand corrected. Make a pic outside, in broad daylight, with the camera set in 'macro' mode (the icon with the little flower). Maple is still excellent wood! So don't be frightened. The design of the bow just depends on the wood species (although maple and hickory both handle similar designs pretty well).
