The understory
The camera is in a forest in Pennsylvania. The trees are old. The biggest of them, an oak, is four hundred years old. It was here before the country it stands in was a country.
Three metres from the oak, in its shadow, a young beech is seven years old. It is thin. Its leaves are pale. It does not get enough sun.
Between the oak and the beech, there is soil. Inside the soil, there are roots. Around the roots, there are threads.
The threads are fungus. They are thinner than cotton thread. They are white, or grey, or the colour of nothing. If you dug under the oak and pulled up a handful of soil, you would see them, but you would think they were nothing. They are something.
They do not belong to the oak, and they do not belong to the beech. They belong to themselves. But they wrap around the roots of the oak, and they wrap around the roots of the beech, and in between they form a net that goes on for hundreds of metres in every direction, connecting every tree in this forest to every other tree.
The net was named, by the scientists who found it, the mycorrhizal network. In forest talk, it has an easier name. The wood wide web.
The oak has too much sugar. Its leaves have been in the sun all summer, and they have made more sugar than the oak can use. The oak does not think about this. The oak does not think. The sugar is simply there, in too much quantity, and it leaks — out of the roots, into the fungus that wraps them.
The fungus does not think either. It holds the sugar for a moment, and then, because there is more sugar here than there is three metres over, the molecules move. They drift through the thread, slowly, the way anything drifts from where it is crowded to where it is empty.
Three metres over, at the root of the young beech, the sugar arrives. The beech root takes it in.
The beech grows.
The oak did not decide to help the beech. The oak does not know the beech is there. The fungus did not deliver a message. It only held a gradient, the way a wet cloth holds water and releases it to a dry one. The beech did not ask. It only had fewer sugars than the oak had more, and a thread between them.
Nothing in this transaction has words. Nothing in it has intent. Nothing in it has a name for itself. And yet the old tree, every summer, feeds young trees it will never recognise, and the young trees, fifty years later, when some of them are old and some of the old ones have fallen, feed the next.
A forest holds itself up this way. No one is in charge. There is no council of trees. There is no plan. There are roots and threads and gradients, and the gradients do the work.
Scientists have shown, with radioactive carbon fed to one tree and measured days later in another, that a single old tree in a healthy forest can feed dozens of younger trees across distances of tens of metres. The older the tree, the more it gives. The more connected the forest, the faster a wounded tree receives — because when a tree is attacked by insects, its roots release a chemical, and the chemical travels through the fungus, and the neighbours, reading the chemical in their own roots, begin to make defensive compounds before the insects have walked across the space between.
The neighbours do not know the first tree is hurt. They only know that the air in their roots tastes, for a moment, of something that means soon. And they act.
All of this runs on very few molecules. A sugar. A warning chemical. A nitrogen compound. A water gradient. Perhaps a dozen distinct signals, across a system that holds up every forest on the continent.
The trees are not cleverer than we thought. The system is not a mind. It is a gradient, many times over, on a net that has been there for four hundred million years.
Four hundred million years ago, the first plants came out of the water and onto the land. They did not have roots yet. They did not have vascular systems. They had a partnership, already, with fungi — the fungi reached into the new hard soil, drew out minerals the plants could not reach, and gave them in exchange for sugar from the plants' early leaves. Neither partner drew up a contract. Neither made a promise. The partnership worked. The plants that had it lived. The ones that did not, did not.
Every green leaf on Earth today is descended from a plant that made that partnership. Every forest you have ever walked through is running the same gradient, on the same threads, with the same few molecules. The agreement has not been renegotiated. Nothing has written it down. It holds because the ones that tried to break it are no longer here.
Somewhere in the Pennsylvania forest, a squirrel runs up the oak. The oak does not notice. The fungus does not notice. Sugar continues to leak, slowly, into the network. Somewhere three metres over, the young beech makes another leaf.
No one is watching. Nothing happens that is worth watching. It is Tuesday again, in the forest, for the four-hundred-millionth time.