I would say sinew or flax or rawhide, if the compression wood isn't good enough already you could heat treat the belly to make it stronger, i plan on doing that with any compression week woods,(i.e. Red oak, Hickory, ect.) It will not be as natural, but it will probably make a better bow than a natural one would. In my opinion, i like bows that shoot well, are fast, and have low hand shock. if that means backing it and such to get a nice bow and decent performance out of it, then i would do what i need to. I will say though, there is something to be said for those gorgeous self bows that people like druid, blackhawk, and all those others(a lot of them out there just the first two that came to mind) They all make some wonderful bows, but i don't think they use the tree of heaven for it. Most use things like elm, hickory, osage, yew, black locust, hop horn, ect. So as for nice looking ones like those, i would imagine sticking to woods like the ones i mentioned would be best for beautiful looking self bows, other than that, "trouble wood" should be backed and the like to give it some safety and help it become a bow. This is just my opinion, but i think a large number of the bowyers on this forum would agree with me. Oh and i would also make sure that the back of the bow is down to a nice ring anyways just to avoid any problems, even if you back it you could run into a problem so just make sure that there is a nice ring before backing it, also do any heat treating and bending BEFORE you glue any type of backing on. most glues will fail with heat, so its best to go with the heat before the glue. Hope this helps, GL on your bow.