How Do Trees Talk to Each Other?

You see one tree getting eaten by insects, while the tree next to it looks untouched. How could the second tree possibly know there’s danger nearby? Trees can’t talk, shout, or send messages. But they can release tiny signals into the air that other trees may detect. And underground, their roots can connect with huge networks of fungi. So are trees actually warning each other? Are they sharing things through the soil? And how much of this is really communication, rather than just trees reacting to what’s around them?