The author quotes "Scandinavian Birch", but according to Google and The Wood Database there's no such thing.
However, there are a few species of Birch that do grow in the area known as "Scandanavia", so it is probably more of a nick name (or marketing title) for one or a combination of those variations.
To be sure, though, I've never found reference of a specific specie that was called Scandinavian Birch.
Elvis you are correct it's a marketing term. From what I have been told the aircraft industry birch as they also refer to it is only found in that part of the world. It has to do with the soil and the cold climate, but Scandi birch is market hype and not an actual species at least in the Sonor world.
...and yet I found no hit in that link that defined "Finnish Birch" to a specific species.
Here's the Birch link from The Wood Database.
It's actually to Alaska Paper Birch (listed alphabetically, so..."A"...), but if you scroll to the bottom you'll see a list of all the other Birch species they list.
Chances are good, the "Scandinavian Birch" could be the "Baltic Birch" they list, as they say it too is not a specific species, but rather a general trade name for Birch plywood made from Birch trees from Russia, Finland and the nearby Baltic states.
The birch typically used for drum construction should be Sweet Birch, although Yellow Birch is also quite popular to use, as well.