Willow chips/shavings are our family choice for hot smoking fish. For meat, usually oak for game meat (venison, moose wild pigs), apple tree for beef & (domesticated) pork.
In Finland or SoCal? Never heard of anyone smoking with willow in Finland, but I suppose it's possible (willows are more like bushes than trees in Finland).
Alder is the actual traditional smoking wood in Finland. For instance, it's what you are legally reguired to use for genuine sauna-cured ham (aito saunapalvikinkku). This traditional recipie also uses alder for bit of smokey flavor:
https://www.unrealworld.fi/forums/index.php?topic=7171.0Beech seems to be modern period import to manor (kartano) gardens. As are apple (you might find some wild relative in the archipelago) and cherry. Oak only exist in the extreme south.