Six-trillion tree claim

This part of the article would be stronger if it explained how the researchers came to the conclusion that there were double the number of trees 12,000 years ago.

That is a major claim that has political and ideological implications.

Though it is likely credible because the researchers undoubtedly used rigorous methods, this would be stronger and more credible to readers if the method of deriving that figure were explained.

While the claim is attributed to the study, it would only pass the "How do you know that?" test on a low level because it's a "He said that" answer.

It would be of interest to know how they came up with the estimate, yes. The sources didn't provide that information; the abstract says something about it being based on projected tree densities, but honestly it's not clear what that means. What we know is that the researchers made such a claim, which we duly reported; it's both reasonable for us to report that they said that, and important that we attribute the claim — attribution being an important part of news neutrality.

Hm, well, maybe. A source does seem to indicate that they estimated forest cover and used the densities they'd come up with for this study.

It's the big question I had writing it, too. It feels like an impossibility to me, to have any real concept of what populations were 12,000 odd years back. Nonetheless, that's the figure they offered.

All in all it seems straight-up odd also that multiple studies have apparently, presumably independently, come up with the 400 billion figure. There's a lot going on here that I'd have loved to have had the time to dig deeper into.