The mycorrhizal networks are a real phenomenon, and as recently as 2016 were confirmed to share resources between trees.

Researchers exposed certain trees to a specific carbon isotope and found their unfed neighbors were processing that specific isotope despite not being exposed.

We've also found that many plants generate interacting electrical fields that help promote pollination and may indicate to pollinators which plants are ready to be harvested.

We've also found, by sequencing fungal DNA, that mother trees do have a resource sharing preference for their direct offspring.

We don't have hard evidence for direct communication between trees, in the sense that we don't speak tree. We do have hard evidence that they share resources, have preferences, express pain signals externally and other plants react, and can indicate information to other species.