Memes

I am under the impression that trees don't actually produce that much oxygen. That they're more like carbon banks, storing it as they grow and then releasing it again when they die, rot or burn down. Meanwhile most of the oxygen produced actually comes from algae and other sources.

Source: some old memory of something I heard, so take it with a grain of salt. It would explain these things tho, beyond the cases where growing a tree would be impractical.