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The matter is conserved: it becomes soil. Most of the carbon an individual plant absorbed when it was growing will become soil when it dies and decays. (Shoul

The matter is conserved: it becomes soil. Most of the carbon an individual plant absorbed when it was growing will become soil when it dies and decays. (Should note "absorbed" here refers to the carbon that became part of the structure of the plant - not the carbon the plant breathed in. Plants breath out most of the carbon they breath in.) Yes, it releases some of it during the decay process, but a lot of it (most of it) does get sequestered even after death. That's where humus comes from. And it's pretty easy to meassure that. And for deciduous trees, they are sequestering yearly as the leaves they drop decay. It wouldn't surprise me if the amount that is being sequestered is being overestimated in many studies, but the mechanism for it happening is pretty clear and that it is happening is pretty incontrovertible - it falls right out of the chemical math - and I would be much more likely to question any study that questioned that than to question that mechanism itself. It's really frustating to me that what is being posted here is basically just a headline and not even an abstract unless you have a subscription to Nature.

goodcanadian 5y ago
Yes, but bacteria action continues in that soil and continues releasing CO2 for a long time to come. Some of it will feed new plants (anything taken from the soil is not being taken from the air). The question is how much of that soil carbon truly becomes permanently sequestered? Some of it may be there for a long time, but the humus layer will not become infinitely thick. Once we are talking about an old growth forest, the forest will have reached a somewhat steady state. I am not saying it cannot continue to act as a carbon sink, just that I suspect it to become less effective over time, and that it will not work in all conditions. A number of research papers have pretty much shown this lately, not just this one.
- jvanderbot 5y ago
  Assuming rich soil accumulates over time in a long-running forest, what happens to the lower layers? Do they release carbon more quickly as they "die" or do they store it? If they store it, then that's sequestration, right?
  - vkou 5y ago
    It is sequestration, but it can take thousands of years for an inch of rich soil to accumulate in a 'steady state' system. Most fossil fuel carbon was originally sequestered in a world where very few things could break down dead trees. That world is millions of years gone, current natural carbon sinks are 99% temporary.
    - saalweachter 5y ago
      There's a certain argument to be made for timber farming as a way to extend our temporary carbon sinks -- trees that fall over rot, releasing their carbon, trees that are cut down and turned into houses may be protected from decay for tens or hundreds of years. You could really go whole-hog into attempting to maximize the amount of timber you can stuff into a house -- start building double-stud walls with 12 inch on-center spacing just to triple the number of 2x6's used, fall in love with giant cross-laminated timber panels, etc etc.
      - vkou 5y ago
        That is incredibly labour and energy-inefficient. You're better off burying raw timber, as opposed to processing it, cutting it up, transporting it to a worksite, and paying professionals to hammer it into place.
        saalweachter 5y ago
        How do you feel about baking the timber in solar ovens first, before burying the charcoal, to go full terra preta?
      - elihu 5y ago
        It seems to me that the low-hanging fruit is to sequester the sawdust and scraps that result from sawing logs into boards. I assume that much of that ordinarily finds its way into other products (paper, particle board, etc...), but that it's economically less valuable than usable boards and thus burying it the ground has lower cost. There does seem to be increasing interest though in making large structures out of wood, so maybe that's a pretty good route for carbon storage.
BurningFrog 5y ago
> The matter is conserved: it becomes soil. So for that mechanism to work, the ground level in old growth forests would slowly rise over the centuries, and more and more soil with some carbon content accumulates. Is that what actually happens?
- ph0rque 5y ago
  Some soil accumulates. Other is washed out to lower areas of elevation. My guess is it's another thing that reaches steady state.

goodcanadian 5y ago

Yes, but bacteria action continues in that soil and continues releasing CO2 for a long time to come. Some of it will feed new plants (anything taken from the soil is not being taken from the air). The question is how much of that soil carbon truly becomes permanently sequestered? Some of it may be there for a long time, but the humus layer will not become infinitely thick. Once we are talking about an old growth forest, the forest will have reached a somewhat steady state. I am not saying it cannot continue to act as a carbon sink, just that I suspect it to become less effective over time, and that it will not work in all conditions. A number of research papers have pretty much shown this lately, not just this one.

jvanderbot 5y ago
Assuming rich soil accumulates over time in a long-running forest, what happens to the lower layers? Do they release carbon more quickly as they "die" or do they store it? If they store it, then that's sequestration, right?
- vkou 5y ago
  It is sequestration, but it can take thousands of years for an inch of rich soil to accumulate in a 'steady state' system. Most fossil fuel carbon was originally sequestered in a world where very few things could break down dead trees. That world is millions of years gone, current natural carbon sinks are 99% temporary.
  - saalweachter 5y ago
    There's a certain argument to be made for timber farming as a way to extend our temporary carbon sinks -- trees that fall over rot, releasing their carbon, trees that are cut down and turned into houses may be protected from decay for tens or hundreds of years. You could really go whole-hog into attempting to maximize the amount of timber you can stuff into a house -- start building double-stud walls with 12 inch on-center spacing just to triple the number of 2x6's used, fall in love with giant cross-laminated timber panels, etc etc.
    - vkou 5y ago
      That is incredibly labour and energy-inefficient. You're better off burying raw timber, as opposed to processing it, cutting it up, transporting it to a worksite, and paying professionals to hammer it into place.
      - saalweachter 5y ago
        How do you feel about baking the timber in solar ovens first, before burying the charcoal, to go full terra preta?
    - elihu 5y ago
      It seems to me that the low-hanging fruit is to sequester the sawdust and scraps that result from sawing logs into boards. I assume that much of that ordinarily finds its way into other products (paper, particle board, etc...), but that it's economically less valuable than usable boards and thus burying it the ground has lower cost. There does seem to be increasing interest though in making large structures out of wood, so maybe that's a pretty good route for carbon storage.

BurningFrog 5y ago

> The matter is conserved: it becomes soil. So for that mechanism to work, the ground level in old growth forests would slowly rise over the centuries, and more and more soil with some carbon content accumulates. Is that what actually happens?

ph0rque 5y ago
Some soil accumulates. Other is washed out to lower areas of elevation. My guess is it's another thing that reaches steady state.