How the fungi beneath our feet help decide the trees overhead
Walking around the Wayne National Forest, you can see mushrooms growing on the sides of logs or from the ground. Molly Jo Stanley, southeast Ohio regional director for the Ohio Environmental Council, pointed to a patch of bright orange ones with large trumpet-like tops.
“Oh, chanterelles!” she exclaimed.
Some are good to eat, but that’s not the only reason they’re exciting to her. “These have a synergistic relationship with these oak trees and these root systems,” Stanley said.
Some mushrooms, or fungi, decompose litter in the forest, like fallen leaves and logs, while others, like most chanterelles, have what are called mycorrhizal connections. This type of fungus has a mutually beneficial relationship with certain species of trees, like oak.
Different fungi mean different trees
But there’s concern about the future of oak trees. While there are many mature oaks in eastern forests in the U.S., there aren’t many young ones. Experts largely blame the lack of fire, which benefits oak tree growth. If nothing is done, the White Oak initiative, a cooperative effort between forestry experts and industry, says oaks could decline significantly in 10 to 15 years.
To remedy this in the Wayne, the U.S. Forest Service has a plan to cut some 2,700 acres in the forest, including 1,600 acres of clearcut.
The OEC argues that it won’t work and is suing to stop it. The lawsuit claims that if oak trees are clearcut, they will be replaced by maple, beech or poplar trees. One piece of evidence the OEC uses is the emerging research about those underground relationships between trees and fungi.
“I was shocked. I was like, ‘wait, what?'” said Jared DeForest when he heard about this legal argument. DeForest is a professor of ecosystem ecology and a geochemist at Ohio University in Athens, which is in southeastern Ohio, near the Wayne.
“It’s not like I have hidden knowledge, but how do you know about that?” he asked.
While not everyone is aware of the research into these underground associations, mycorrhizal fungi are very common in forests.
“Pretty much 90% of all land plants are associated with some type of mycorrhizal species,” he said.
This underground network has been a big and important discovery about forest health over the past 20 to 25 years, according to DeForest.
When he first heard about it, he could hardly believe it.
“I was generally taught it’s all about competition. It’s like a war out there with all these things,” he said. “And the more I realize this is facilitation, these things are communicating. It’s a collective whole.”
There are still many open questions for researchers, like, are the trees helping each other, communicating about things like disease?
But researchers have been able to connect different trees with two types of mycorrhizal networks, ectomycorrhizal and arbuscular mycorrhizal.
Arbuscular mycorrhizal, considered scavengers, are connected with maples, tulip poplars and black gum trees. “Those leaves decompose fast. And so what [arbuscular mycorrhizal] is all about is scavenging that stuff up, making things more nutrient-rich, speeding up the cycling of nutrients, and then [those trees] can grow bigger and faster,” DeForest explained.
The other types, the ectomycorrhizal, associated with oaks and hickories, are considered “miners.”
“Those are the ones that actually slow down decomposition. They mine out the nutrients, and they suck it up,” he said, calling this type of soil “crummy.” “These systems are actually nutrient-poor. They want to keep it nutrient-poor because that’s what they do best.”
If a forest is clearcut for lumber or to manage trees, what grows back depends partly on the soil, according to DeForest. In poor soil, you are more likely to get oaks. In more nutrient-rich soil, he says the seedlings of arbuscular mycorrhizal-connected species would do a bit better.
How pollution and climate change impact fungi
In his own research, DeForest has looked at how electrical power generation impacts forests, and he finds that pollution and climate change are factors in what grows in forests.
“Coal produces a lot of nitrogen and nutrients actually fall from the sky (natural gas, not so much), that it’s altered the soil condition to make it more nutrient-rich, and the more nutrient-rich soils are, it favors those scavengers, arbuscular mycorrhizal species like maple,” he said.
“Also in this area, due to climate change, it’s getting wetter and that’s also one of these contributing causes because oaks, beech, pines, they do really good on dry sites, but now things are getting wetter. And Maples, tulip poplar, arbuscular mycorrhizal, do a little bit better on wetter sites,” DeForest said.
So, even though oaks have had a strong presence in eastern forests, this new science around underground networks helps explain why groups like the White Oak Initiative and others are worried about its decline in the coming decades.
“We go back 100 years, we clearcut it, and all the oaks came back,” he said. But, “the climate was different, it was drier, there were less nutrients. We’re getting to the point that maybe it’s going to be we’ll still have oaks, but it’s not going to be as dominant is what it was 100 years ago,” he said.
In DeForest’s view, the increase of maples is just another step in the evolution of our forests.
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