The Broker

The postdoc's name was Risa, and she had not slept in two days.

This was obvious from the four empty coffee cups wedged between her laptop and a soil moisture probe, and from the way she kept squinting at her screen like it had personally offended her. She had invited Maya and Soren to the research forest because their school's science fair required a mentorship component, and she needed, as she put it, someone to hold the other end of the tape measure.

They had been holding tape measures for three hours. Risa had not explained a single thing she was doing.

"Something's wrong with tree forty-seven," Risa muttered, mostly to herself. She tapped a line on her screen. A jagged green graph climbed, fell, climbed again.

Soren looked at Maya. Maya was already looking at the screen.

"Wrong how?" Maya asked.

"It's getting too much." Risa rubbed her eyes. "We labeled the carbon. Carbon thirteen. Fed it to tree twenty-two over there." She pointed vaguely toward a Douglas fir with orange tape around its trunk. "We track where the labeled carbon ends up. It moves through the mycorrhizal network, the fungal threads in the soil. Tree to fungus to tree. Fine. Normal. But forty-seven is pulling way more than its neighbors."

"Maybe it's closer," Soren said.

"It's not closer. Tree thirty-one is closer. Thirty-one is getting almost nothing." Risa stared at her data. "I think my sensors are drifting."

She walked off to check a junction box at the far end of the plot, leaving her laptop open on the folding table.

Soren sat down in front of it.

The screen showed a map of the research plot. Sixty trees, each a numbered dot. Lines connected them, showing where the fungal network linked root to root. The lines were colored by how much labeled carbon had moved along each connection. Most were pale blue. Almost nothing. A few were brighter. And three lines leading to tree forty-seven were vivid, hot orange.

"She's right," Soren said. "Forty-seven is getting a lot."

Maya was walking between the trees, looking up. She stopped at tree thirty-one, the close one that was getting almost nothing. She tilted her head back.

"Soren. Come here."

He left the laptop and walked over. Tree thirty-one was a Douglas fir like the others, but its crown was thin. Sparse. Patches of sky showed through where there should have been dense green.

"Now look at forty-seven," Maya said.

They walked together to the orange-lined tree. Forty-seven was enormous. Its crown was so thick and wide it shaded out a circle of ground fifteen feet across. Every branch heavy with needles, dark green, almost black-green in the afternoon light.

"Forty-seven is huge," Soren said.

"Forty-seven is making a ton of sugar," Maya said. "All those needles. Photosynthesis. And thirty-one, the thin one, is barely making any."

Soren stopped walking. "Wait. That's backward."

"What is?"

"If the network was just, like, a pipe. Water flowing downhill. You'd expect the carbon to go from where there's more to where there's less. You'd expect thirty-one to get more because it needs more. That's how you'd share."

"But forty-seven is getting more," Maya said. "And forty-seven already has more."

They stood there, both of them looking up at the thick crown.

"Unless," Soren said, and paused, and Maya did not fill the pause, because she was thinking the same thing and wanted to hear how he'd say it. "Unless the fungus isn't a pipe. Unless the fungus is choosing."

"Choosing what, though."

Soren pulled his notebook out and flipped to a blank page. He drew two circles. One big, one small. He drew lines from a central point to both.

"Okay. The fungus connects to the trees' roots. The fungus gives the trees nutrients, phosphorus, nitrogen, whatever. And the trees give the fungus carbon. Sugars. That's the deal."

"Right," Maya said. "That's the basic mutualism."

"So if you're the fungus. And you've got two trading partners. One is making a huge amount of sugar and can pay you back a lot. And one is barely making any sugar and can barely pay you back." He tapped the big circle with his pencil. "Where do you send your resources?"

Maya's eyes went wide. "You send them to the one that's going to pay you back the most."

"The fungus is investing."

They looked at each other across the notebook. The forest was quiet except for a Steller's jay screaming somewhere in the canopy.

"That's not sharing," Maya said slowly. "That's trading. That's, like, a market."

"A market where the fungus is the broker," Soren said.

Maya turned in a slow circle, looking at the ground. Soil. Duff. Dead needles. Under all of it, a web of fungal threads thinner than hair, connecting every tree in the plot. Not a community garden. Not a sharing circle. A trading floor, and the traders were not the trees.

The traders were invisible.

"Soren. How many species of mycorrhizal fungi are in a forest like this?"

"I don't know. Hundreds?"

"Hundreds of brokers. All cutting their own deals. All deciding where the carbon goes."

Soren wrote: Not a network. A marketplace. Then crossed it out and wrote: Both. He stared at it.

Risa came back, holding a sensor that she'd apparently pulled out of the ground. Dirt crumbled from its tip.

"Sensors are fine," she said, sounding annoyed. "Which means the data is real, which means I have no idea why forty-seven is pulling so much."

"We think we do," Maya said.

She explained it in four sentences. Risa blinked. Looked at the canopy of forty-seven. Looked at the canopy of thirty-one. Sat down on a stump.

"That would mean the fungus isn't just connecting the trees. It's managing them."

"It's managing you, too," Maya said. "It's deciding what your data looks like."

Risa stared at her for a long time, then laughed once, short and sharp, and opened a new file on her laptop.

A breeze moved through the high branches, and the whole crown swayed, heavy and dark and fed.