Another perspective on the same events:

We didn't lose the bison, we exterminated them, deliberately, in order to starve out the Comanche. Once we starved out the Comanche, we were able to convince the poor and downtrodden of the East Coast to expand into the Great American Desert. Once we'd expanded into the Great American Desert and turned it into "the Great Plains", we encouraged people with no idea about farming to cut up all the buffalo grass and plant corn and wheat. Which, once it stopped raining, led to massive desertification and the only way we had any clue about controlling it was the Shelterbelt, still our largest public works project even after 100 years of the Army Corps of Engineers went about damming every body of water more than a few inches wide.

"Converted to farmland or other private land use" doesn't make that land use holy, it makes it inefficient. Governments generally subsidize annual cereal crops because they're portable and can be stored. Governments generally reserve perennials for luxury because you have to be a wealthy mutherfucker to plant an apple orchard and know you won't see a dime for six years.

We've spent $113b on corn subsidies since 1995. Using "20 million trees" metrics, that's 113 billion trees - ten percent of the number mk landed on - just from corn subsidies.

A little math: one cow in Brazil requires one hectare. One cow in Brazil pulls down 23 real per kilo - or $6. U of Oklahoma figures you're looking at 430lbs of viable meat per steer, or 195 kilos, so you're looking at a market price of $1200 per hectare per cow. Cattle mature after eighteen months so you're looking at $800 per hectare per year.

$70b a year to lock off the 16% of Brazilian amazon to replant it is one tenth what the US spent on defense in 2018. It's three times what NATO is budgeted for. It's 3% of Brazil's GDP. here's the thing: if the wealthy nations of the world decided to lock off vast swaths of the Amazon in trust? You'd see some real change. Shit, if we got all the ranchers and cattle farmers to stop raising cattle and subsidized the planting of perennials we'd likely be golden. And no matter how long something's been farmland, it wasn't farmland to start with and it wasn't farmed by anyone further back than that farmer's grandfather.

we need to ask questions such as "why is the ecosystem now different and is that different good or bad" and "would planting trees here be beneficial or detrimental?

We don't need to ask any of these questions because simply asking them presumes that there's some sort of ancestral right to grow cattle in countries that didn't even have cattle eight generations ago.

Now if you'll excuse me, I need to go buy some beef.