Beavers: European v Canadian

I recently took this photo of a birch tree in the Patvinsuo National Park in Finland. It shows the work of a beaver, but this is not the work of a European Beaver Castor fiberis as you might expect, but rather that of a Canadian Beaver Castor canadensis (aka North American Beaver). Such field signs are identical for both species but it is know that this area and indeed most of Finland only has the Canadians, which where introduced to Finland when the locals became rare due to trapping.