Thanks, that's interesting. I mostly agree. I'm not sure the dominant tree species would vary much, as Finland's forests, both old growth and managed, are mostly scots pine, norway spruce, and birch -- which looks to be what we see here in both the old forest and the trees around the edge of what Google cleared.

Definitely an older forest will have more complexity and thus diversity of understory etc.

I imagine a lot of the beneficial aspects of old forest, e.g. structural complexity, snags and downed logs, canopy gaps where trees fell, etc will develop on their own given time, in many of Finland's managed/logged forests. I think this is what we see in the "old forest" examples. And it is what I've seen in the areas I've lived in the USA. And, humans can try to help these things develop sooner, which like you say is often expensive and complex.

Some places like California, eucalyptus will come in and completely take over some forested areas after they're cleared, and so it won't naturally become like old native forest again. I don't think they have something quite like that in Finland but I'm curious if they do. I don't know what will happen with these patches of eucalyptus in another few hundred years if humans don't intervene.