I don't think you should get much ammonia from a piece of wood. Wood is mostly lignin and cellulose, which are primarily made up of Carbon and Hydrogen (maybe some Oxygen?), Nitrogen is mostly found in proteins, which won't be very abundant in wood.
anyways, I'd soak things for a bit just to get some of the tannins out, help get it waterlogged, and make sure there isn't much sap/resin left in it. then give it a good scrub, mount it on a piece of slate, and put it in your tank.