I'd have to guess specie matters as well. I recently found a stand of rock elm in my area and took some of those. When I split some very clean saplings, they cloves in two halves, with the splits so clean a little sandpaper would have had them smooth and flat. I wouldn't have hesitated to work out a QS backing with that split as the back of the bow from that thing, but it was such a good stave, I just used it.
On the other hand, most of the "red" elms would be totally unusable, with their stringy, ragged grain, and small knots everywhere.
