Many wood species are fine to make scales. Since the wood needs to be coated with some durable finish, natural durability is not much of an issue. Hardness may be more of importance, but even that can be coped with by the type of finishing.
From an environmental and cultural viewpoint, a lot can be said in favor of native species.
Some people don't like altering the natural color of wood, but if the final result looks great, I always wondered what the big deal about that was.
Some woods can be burnished to a rich, very dark color, before being finished. Olivewood works great for that.
Another very attractive wood species growing in Portugal is Taxus. It has a strong contrast between sapwood and heartwood, something that allows for neat design effects.
Image:Taxus wood.jpg - Wikimedia Commons
Just a few random thoughts on the subject...
Kind regards,
Bart.