Stretch explanation: in popular culture the chestnut tree served as a major plot point in Richard Power's 2018 novel The Overstory, which won several major awards. His most recent novel was published in late September, so to some extent his name and plots are back in the news.
Stretchier explanation: Frequency illusion, also called Baader–Meinhof phenomenon. Per Wikipedia, "a cognitive bias in which, after noticing something for the first time, there is a tendency to notice it more often, leading someone to believe that it has a high frequency of occurrence"
It's probably Baader-Meinhof plus an actual increase in frequency, which can happen if people see an interesting link on NH and then share it socially on other sites (which then gets shared further). Interesting topics seem to be fairly "bursty" among various social networks.
Yeah, I've been aware of the demise of the American chestnut tree for years now, but I'm just seeing it in heightened frequency lately. You're right that social networks can get bursty.
I think it might be very simple. It only takes a couple of votes for a story to hit the front page. Those votes could have come from people like you who are on both sites. Once something hits the front page here, people seem to take it more seriously, which is a bit of a shame since so many quality submissions just slide off the new page because they fail to get the 2 or 3 necessary upvotes.
The responsible upvote on /newest was probably mine. I always upvote the chestnut things I see because I greatly admire it as an example of long-term thinking/projects and the benefits of selective breeding & genetic engineering, and of course the history angles are just cool.
Funny how knowledge spreads on the internet.