It's actually pretty clear from new imagery the Amazon was significantly deforested and farmed before European diseases wiped out the natives.
And before that, the extinctions mammoths and mastadons (by humans) led to a lot of tree cover that was grassland when the grazers kept the forests in check.
There was an interesting discussion on HN not too long ago (1-3 months?), that we have been wrong about human stress on mammoths etc. We should find it. As usual we learn neat things on HN.
And before that, the extinctions mammoths and mastadons (by humans) led to a lot of tree cover that was grassland when the grazers kept the forests in check.