You’ve probably heard the line that forests are the lungs of the planet.
The metaphor is sort of backwards, since lungs take in oxygen and release CO2 (with other things), while trees do it the other way around. But it’s a useful reminder of how the world’s gazillion trees are vital for balancing atmospheric chemistry.
The prospect of them getting a version of arboreal black lung is terrifying, but that’s what new research out of the University of New Hampshire hints is happening in the northern forests.
“Something is happening in soils as they warm that has shifted the way the whole system absorbs and releases carbon,” said UNH Professor Scott Ollinger, one of the researchers who worked on this disturbing project.
Before we get to the biology/chemistry details, note that this finding could also take a financial toll. The multi-billion-dollar carbon sequestration industry depends on forests absorbing certain amounts of CO2. If it turns out that this calculation is wrong, that some forests aren’t actually absorbing much greenhouse gas or are actually releasing it, then a whole lot of global contracts may have to be rewritten.
The research, published in Global Change Biology Communication, is based on 20 years of data taken from the Bartlett Experimental Forest near Conway. The forest has been preserved and studied since 1931, creating a unique long-term record of the region’s dominant ecosystem. Along with a similar forest at Hubbard Brook, it is one of the gems of New Hampshire.
Among the research tools at Bartlett is a 120-foot tower erected in 2004, which continuously monitors the amount of carbon dioxide going in and out of the ecosystem. Researchers figured two decades of data were worth a look — but when they did, they found something alarming: The carbon sink strength, a measure of how much carbon is absorbed from the atmosphere, has declined. A lot.
At the start, Ollinger said, the forest was taking up roughly 200 grams per meter squared of carbon annually, or roughly half a pound per square meter per year taken from the atmosphere, where it contributes to the climate emergency, and stored as biomass.
“That number has declined significantly and pretty quickly. The trend is very strong, and it’s to the point where now it’s averaging roughly zero,” he said.
In other words, this stretch of the northern forest has stopped absorbing carbon from the atmosphere. One of the buffers we’ve been using to slow down global warming is broken.
Researchers’ first thought, Ollinger said, was that the change just reflected natural aging. “It’s not unusual for forests to sequester less as they get old. Trees can only get so big, and the death and decomposition start to match the photosynthetic rate.”
But that’s not the case at Bartlett, which is still recovering from the logging of a century ago: “It is still putting on new biomass. The growth rate is still quite a bit higher than the death rate.”
What seems to be happening is that the soil is releasing more CO2 — breathing it out, so to speak, which explains the research paper’s title: “Increasing Respiration Weakens the Carbon Sink Over Two Decades in a Temperate Deciduous Forest.”
The research was led by Andrew Richardson, a professor at Northern Arizona University and a former postdoctoral associate at UNH, and Darby Bergl, a doctoral student at NAU, as well as Ollinger.
“Last summer, we initiated a field campaign, going back and explicitly measuring respiration from soil, the fluxes right out of the soil. We do see that the soil respiration is higher than it used to be,” Ollinger said.
Exactly why is unclear and will take more research on the ground, Ollinger said. Maybe it’s something to do with soil microbes, the way all the leaves, branches and other organic matter are continuously broken down.
“Maybe it’s the roots. Maybe trees are working harder than they used to, putting more effort into their root systems to access more nutrients and water in the soil,” Ollinger speculated.
That’s a plausible hypothesis because of climate change’s shorter winters, less snowpack and more extreme floods and droughts. All those nasty changes could be stressing the trees and making them breathe a lot harder. If so, it would be another example of a negative climate feedback, with warming ecosystems reducing a practice that keeps them from getting warmer.
“We’d really like to know specifically what’s driving it,” he said. “We’d have to go into the woods every year and measure things individually, but we’ve never had enough funding to go out every single year to look at that.”
As you may know, the Trump administration’s war on science, part of its goal to make America ignorant again, has targeted the Bartlett Experimental Forest for closure.
Perhaps the fact that this research has an effect on money rather than just the environment will give Bartlett enough value to be spared.
Perhaps.
