Forest carbon basics
When you’re walking through a forest, what are you actually looking at? Surprise! It’s carbon. It’s all carbon — by weight all but a few percent of the forest’s live carbon is stored in wood. All those nice ferns in the understory? Bubkis. Even within a tree, 95 % of the carbon is stored in the woody body of the tree, with the other 5 % in leaves. Wood is quite simply just carbon and hydrogen, both of which come from the atmosphere. So the stuff that makes up a tree is almost entirely sourced from the air.
Wood’s only purpose in life is to shuttle materials between the leaves and the roots, and to support the tree as it grows towards the sun. So to fulfill that purpose, wood doesn’t need to have much going on. Therefore, most wood cells are essentially dead. As the tree grows those new rings every year, it evacuates all the important nutrients, cell organelles, DNA, ect… from the older wood, leaving just a hollow tube of carbon and hydrogen in place.
Now we all know that photosynthesis is responsible for removing CO2 from the atmosphere to make sugars to feed the tree, but what’s often left out of that is the other side of that equation: The trees need to eat the sugars! So trees respire just like humans and return almost all the CO2 that they’ve taken out of the atmosphere back to it. Only a tiny fraction of the CO2 that a tree goes through in a day will be locked away, stored as wood as the tree grows.
This is important to understand because as trees get older, the amount of CO2 that they’re able to lock away diminishes. Eventually, really old trees are giving out as much CO2 as they’re taking in. They’re no longer growing, just maintaining themselves. That means that trees grow along an S-curve, where they start slow, then accumulate lots of carbon as they grow rapidly, then senesce and hit an equilibrium.
And the same thing actually happens to ecosystems! Old growth forests are not removing carbon from the atmosphere. Young trees grow, they absorb CO2, they senesce and slow down, and then they die. When they decompose and all that carbon goes back into the air, and young trees grow anew in the gap that was just formed. Old growth forests are steady-state systems, and they kinda have to be, don’t they? Otherwise, where would all that carbon go over 50,000 years? The Amazon wouldn’t be a rainforest, it would be a mountain!
A few ecosystems are an exception: bogs, mangrove forests, and arctic tundra. In these cases the carbon literally is being stored in the soil beneath the forests. Lord help us if the tundra ever fully thaws. There are hundreds of thousands of years’ worth of carbon stored there.
plant new trees to remove carbon from the atmosphere as they grow. But we also have to prevent existing forests from being chopped down because they’re stocked full of wood, aka carbon. And voila! We have the basis for the three different types of forest carbon projects: Reforestation which planting trees (duh), Avoided Deforestation which focuses on preventing trees from being cut down, and Improved Forest Management, which takes a middle-aged forest that’s been degraded in the past and preserves it, allowing it to grow. IFM both sequesters carbon from the atmosphere and prevents it from being released.
We do need to consider that forests are not the only carbon capture efforts out there. But how does planting trees actually compare to other carbon capture techniques? Is it worth dealing with the risk, occasional corruption, and bureaucracy of forest carbon projects? Well for example, in September 2021 the world’s largest direct air capture facility came online in Iceland — basically a giant vacuum cleaner sucking CO2 out the air. The best solution that humanity and technology has to offer today.
Except it only removes 4000 tonnes of CO2 per year! That’s about as much CO2 as is stored in 10hectares (25 acres) of rainforest, or about the average size of a Walmart parking lot. For newly planted trees, that’s about as much as 400 hectares (1000 acres) would sequester in a year. So I’d say it’s safe to say that this kind of carbon capture technology has a very long way to go before it can compete with 400 million years of plant evolution.
Ultimately people debate about whether or not nature-based solutions alone can solve climate change. Some scientists think that through reforestation (or afforestation) we can completely remove ALL the carbon that humans have put into the atmosphere. Others think that forests can only help us remove a fraction and should just be one piece of the larger puzzle. Either way though, whether you are planting trees or preserving trees (even in small quantities), there is potential there to offset industrial levels of CO2. So go grab a shovel and get out there and plant a few trees! Consider this — over the next few decades, even a few acres of new forest could undo much of the carbon that you’ve put into the atmosphere over the course of your lifetime.