Iskandros, in my part of the world these are basically weed trees. I'm sure you could find hundreds of already germinated babies in the spring. As to harvesting I don't know for sure, but I'd just collect them when they start flying off the trees in their thousands and sow them immediately. I see no point in climbing into the trees to harvest when they will be raining down in a few more weeks.

Floral, yes they are very prolific and fast growing, but I quite love them. As far as I know the seeds fall off in spring (but i might be wrong) and sometimes can take 18 months to germinate. If I could plant them in early autumn I'd be much happier. The saplings I have will be moved in October, November as the other species.

I think it's when you store the seeds for a while so they dry out completely they might need 18 month to germinate. If you collect them when they fall off the trees, and sow them immediately they will probably sprout next spring. And I agree, they are pretty nice for a large maple. I like them more than the Norway maple that is the other common maple where I live.