Trees to the rescue, even after their death
Research suggests carbon collected by forests ends up in long-term storage
Photo by Haberdoedas on Unsplash
After dropping off my mom off at her Indiana home earlier this month, I sat near a line of trees near where I was staying. Like some trees I saw in Ohio, several of the similarly denuded trees had cracked branches or even treetops.
I peered under one where drooping branches spread around in a half circle like a broom reaching to the forest floor. The edges formed a tent-like structure—a child’s dream fortress.
Even as the child in me recognized a natural fortress, the scientist in me registered how the branches would protect and, in time, improve the soil.
The shift from wood to deadwood and, eventually, soil organic carbon was one of the reasons given in a recent Science paper that the carbon dioxide consumed by the world’s vegetation is more stable than global climate models originally surmised.
Carbon shifting to long-lived pools
Before getting back to the beauty of how dropping branches and falling leaves benefit soil, I’d like to elaborate on the paper published March 20 in Science, led by Yinon Bar-On of the California Institute of Technology.
The author and several Caltech colleagues used multiple lines of analysis to consider how well computer models of vegetation are treating the amount of carbon in the “land sink”—mainly the forests that collect heat-trapping carbon dioxide from the atmosphere and put it into their leaves, trunks and roots.
Their analysis includes but does not focus on plot surveys.
They found much of the carbon dioxide trees removed from the atmosphere now likely exists in forms that are less easily susceptible to decomposition, such as in soil or under water.
Some have hailed the paper as a good sign that the stored carbon won’t be quickly returning to the atmosphere to carry out its old job of warming the air.
Plot-based analysis differs
Admittedly, I’m more inclined to believe the results of a 2024 Nature research paper that focused on plot-level repeat surveys to conclude the world’s forests are absorbing more carbon in part by growing denser.
The Nature analysis by Yude Pan and colleagues pretty much accounted for the carbon picked up by the vegetation. Still, this approach also requires extrapolations, because long-term plots don’t exist everywhere.
“Those tropical countries, they do not have the inventory system like most temperate countries,” Pan told me during a January 23 interview.
She and her colleagues used several hundred tropical plots to estimate carbon dynamics for the region. It sounds like a lot, but this region is so large—and so important for global carbon dynamics—that more plots would be better.
Pan and her colleagues found the forest drawdown of carbon dioxide surprisingly stable over the years, despite accumulative loss of old-growth forests and ever-expanding releases of carbon dioxide.
They attribute this finding in part to “carbon dioxide fertilization,” where trees and other plants actually grow bigger, faster when they are flush with their favorite airborne food.
Where does it end up?
The newer Science research also found an increasing amount of carbon being removed from the atmosphere. A big difference is the authors estimate that much of it ends up in soil and sediments rather than the trees themselves.
It’s encouraging to see Bar-On and colleagues considering the flow of carbon into deeper storage once trees have collected it from the atmosphere.
This is something that’s interested me for a long time, but it’s not nearly as well monitored as the above-ground, visible portion of forests.
As I concluded in my doctoral dissertation and described in a January 20 Eco-Logic post, dead wood can linger on the landscape for decades and even centuries, contrary to what computer models tend to assume. Even when they’re mostly decayed, they’ll leave behind some carbon as soil organic matter.
Bar-On and colleagues acknowledge dead wood and soil as two likely longer-term sinks. But they also point to carbon buried in water and even landfills as an overlooked and relatively stable location for some of the carbon plucked out of the air by forests.
This, too, is something I’ve been thinking about for a while. As I wrote in my 2010 book, Life in the Hothouse: How a Living Planet Survives Climate Change:
Erosion whisks off soil, along with the organic carbon it contains, as well as leaves and other carbon-rich debris. Rivers then deposit some of that carbon into wetter environments where it is less likely to decay.
The organic matter traveling by river that makes it to the seafloor (or lakebed) without being eaten or dissolved can put former carbon dioxide into deep storage.
The Science paper provides more impetus for considering storage outside of the trees. I hope it spurs more on-the-ground research, not just modeling efforts, to determine how much carbon ends up in these different nonliving storage areas.
The answers have implications for our planet’s climate stability.
"The planet is doing us a favor by taking up our excess carbon emissions," as co-author Christian Frankenberg explained. "And because this carbon is apparently stored in these nonliving pools, we can expect the carbon to remain in the land for a longer time."
Great news. I’ll go further: We can also expect the carbon stored in soil to benefit the life forms in and above the soil.
Benefits of storing carbon in soil
Adding organic matter to the soil—including organic matter that started out as branches, logs and leaves—is one of the best ways to improve it. Soil organic matter does a great job of mending poor soils, from clay-filled to sandy.
Every farmer and gardener who has made compost recognizes that some of the carbon from leaves and vegetables will remain behind, nourishing the soil in which the compost sits. The same concept applies to branches and fallen trunks.
Compost and other organic matter add nutrients to the soil. This nourishes animals and helpful fungi as well as plants.
Organic matter also improves soil structure.
It creates bridges among grains of sand, particles so large they collectively act as almost a sieve for water flowing through them. The organic matter slows down drainage, giving plants a better chance at grabbing some water before it slips away.
In clay, organic matter improves the much smaller particles by binding them together into larger clumps. This opens up clay-filled soil, speeding up drainage so it can reach roots rather than puddling on top of soil.
Because of these positive influences on mineral soil particles such as sand and clay, organic matter improves a soil’s ability to hold water and release it to plants. It also aerates the soil, which helps the many critters living in soil and also improving it.
Along with a compost of leaves and branches, roots contribute to soil organic matter. They’re already in the ground, so after they die, they serve as food for soil organisms or storage for soil carbon.
While alive, roots loosen the soil. And they release carbonic acid, which feeds the soil biome and helps to turn rock into soil particles or nutrients for use by plants.
These are just a few of the ways trees contribute to helping to moderate the ongoing temperature rise—by not only taking up carbon dioxide to grow and expand, but also depositing some of it into long-term storage.
Almost everything trees do benefits life.
Even though I suspect the latest study underestimates the amount of carbon retained within trees, it’s nice to see a scientific article detailing some of the other places where carbon collected by trees ends up.
Try as they might—and they’re definitely trying—the tech bros will never be able to devise a substitute that carries out the many beneficial roles of trees.
Just ask my cat.
So beautiful...bridging the wisdom of nature with the information about it gained by science, which is ultimately an explanation of nature's wisdom.
Gives me hope for the future of the planet...and provides knowledge for our species if we want to survive.
I'm here to mostly echo what Allison said, and note how the more we find out the more we realise we do not know about the intelligent self-balancing intricacy of life. And I am always curious about how we listen in for what is each of our roles in that.