The "wood wide web" is a hidden world that exists below the ground and now for the first time a major international study of millions of trees has mapped the underground network.
The roots of trees and other plants are joined by a network of fungi and they work together to help feed and protect each other.
Dr Thomas Crowther who mapped the network with his team told the BBC: "We've relied heavily on satelites for a very long time to understand ecosystems but now we're in the age of big data and machine learning, so by taking data from thousands of people from all around the world we are starting to characterise these incredibly important ecosystems for the very first time."
They can now use DNA testing to tell what is down there.
Ecologist Martin Bidartondo says the underground network "is filled with fungi and the fungi are really good because they're three demensional, they make a network."
Mr Bidartondo says if the network is broken it's bad news not just for the trees but for the planet.
"If we create conditions through changing the types of fungi that are interacting with plants in the soil in which then those soils start to stop accumulating carbon or they start releasing it, the rate at which we are seeing change will accelerate even more."