If you're interested in this subject, Peter Wohlleben published a book in 2015 called The Hidden Life of Trees, What They Feel, How They Communicate. One excerpt from the book relevant to this article:

"The fungus not only penetrates and envelops the tree's roots, but also allows its web to roam through the surrounding forest floor. In so doing, it extends the reach of the tree's own roots as the web grows out toward other trees. Here, it connects with other trees' fungal partners and roots. And so a network is created, and now it's easy for the trees to exchange vital nutrients and even information--such as an impending insect attack" (51).

I look at groups of trees, and trees in general, very differently than I had before I read this book. I'm happy to see this Yale article make it to HN.