I use those timbers a fair bit (not for bows!); they are full of silica deposits, have reverse grain, and spiral grain, and are very brittle. These types of timber are incredibly hard to identify and are frequently mis-identified as various types of walnut and of mahogany, especially when being re-cycled. In general they are best worked across the grain and are easily split when force is applied along the grain, like a bow-string might do, but they don't split cleanly, they break out in chunks, exactly like in the photo. They need enough mass to resist the force, so long, deep overlays should be ok but still, I wouldn't risk it.....
