>Trees exchange chemicals with fungus, and send seeds—essentially information packets—with wind, birds, bats, and other visitors for delivery around the world. Simard specializes in the underground relationships of trees. Her research shows that below the earth are vast networks of roots working with fungi to move water, carbon, and nutrients among trees of all species. These complex, symbiotic networks mimic human neural and social networks. They even have mother trees at various centers, managing information flow, and the interconnectedness helps a slew of live things fight disease and survive together.

>Simard argues that this exchange is communication

That's pretty much the gist of the article without the fluff. I think the term "language" is an extreme hyperbole here, but it's interesting that rudimentary information can be passed between different trees.