[HN Gopher] Old-growth forest carbon sinks overestimated
___________________________________________________________________
Old-growth forest carbon sinks overestimated
Author : tokai
Score : 76 points
Date : 2021-04-21 11:32 UTC (11 hours ago)
(HTM) web link (www.nature.com)
(TXT) w3m dump (www.nature.com)
| aaron695 wrote:
| Always good to remember environmentalist don't care about old
| growth forests or eco-systems or humans.
|
| It's just about CO2 in the air. Not even the measurable amount,
| most can't tell you any numbers.
|
| They have found a way to control the population that will work
| for decades.
|
| Who cares what old growth forests do, why are we even worrying
| about CO2 if it's not about getting old growth forests back? I
| guess because CO2 has become god.
| richiebful1 wrote:
| Here's a non-paywalled summary:
| https://phys.org/news/2021-03-old-growth-forest-carbon-overe...
| henearkr wrote:
| There is already a rebuttal:
|
| https://www.nature.com/articles/s41586-021-03267-y
|
| The rebuttal too is behind a paywall and doesn't have an
| abstract...
| sp332 wrote:
| I think the link is to the rebuttal, right? The original paper
| is from 2008.
| sampo wrote:
| 2008: Original article [1]
|
| 2021: Rebuttal of the 2008 article [2]
|
| 2021: same issue of Nature, next 2 pages: Rebuttal of the
| rebuttal by 6 (out of 8) of the authors of the 2008 article
| [3]
|
| [1] https://www.nature.com/articles/nature07276
|
| [2] https://www.nature.com/articles/s41586-021-03266-z
|
| [3] https://www.nature.com/articles/s41586-021-03267-y
| fshbbdssbbgdd wrote:
| I'm curious if these competing rebuttals get to read each
| other during the editing process. Otherwise will there be
| two more rebuttals in the next issue?
| goodcanadian wrote:
| Some basic conservation of matter arguments apply. As long as a
| plant is growing, it will sink carbon. When it dies and rots, it
| will release that carbon again. So, a growing forest will sink
| carbon, but a steady state one will not. This is why I have
| always been sceptical of tree planting as a carbon offest . . .
| it is short term, at best. Of course, there are a myriad of other
| reasons why tree planting might be desirable.
|
| The caveat to the above is the extent to which dead plant matter
| gets permanently buried (turned into peat or whatever) rather
| than rotting. Under some conditions, forests really will work as
| a carbon sink, but it has never been as simple as tree planting
| == good, and I am glad to see research acknowledging that. As
| with everything, it is complicated.
| njarboe wrote:
| In the California Sierra Nevada mountains almost all of the
| land was harvested for timber in the last 150 years. These
| forests contained mostly trees that were many hundreds to
| thousands of years old. So if we plant the right trees and let
| these harvested forests keep growing, instead of harvesting
| them again, we will get a thousand years of increasing carbon
| capture. I'm not sure about other forest ecosystems, but "short
| term" could be hundreds to thousands of years. A quite useful
| timescale for a large carbon sink as we try to get to a more
| normal atmospheric carbon dioxide level in the future.
| tastyfreeze wrote:
| We can go a long way in removing carbon from the atmosphere by
| regenerating our degraded soils by bringing them back to life.
| Some estimates of atmospheric carbon sources list released soil
| carbon around 40%. Fertile soil is filled with carbon in the
| form of life and decomposing material (food for life). While
| this video doesn't address carbon directly it does show how
| much soil around the world is degraded to the point where all
| life and carbon in the soil is gone.
|
| https://www.youtube.com/watch?v=c4p-kQ6D8aA
|
| Edit: Soil as carbon sink
| https://news.climate.columbia.edu/2018/02/21/can-soil-help-c...
| bamboozled wrote:
| But you can imagine how much a large tree weighs, particularly
| a hardwood, a large portion of tree being made of carbon sucked
| from the atmosphere. Then the foliage becomes soil and buried.
| Plant a trillion trees, you're going to see some changes to the
| composition of the atmosphere over time.
|
| If the forests of said trees are self -regenerating, it's going
| to be a decent sink.
| ravi-delia wrote:
| Naive tree planting definitely isn't as simple a carbon capture
| method as 1 ton trees -> -1 ton carbon, but in current
| circumstances it's still a good idea. For one, thanks to
| deforestation most tree planting (so long as they're planted in
| a sustainable way) is growth, increasing total biomass. For
| another, if I could snap my fingers and offset some current day
| carbon emissions by a few decades, I definitely would. We are
| right against the wall at the moment, buying a bit of time
| could do a lot for us.
| wing-_-nuts wrote:
| IMHO we need to do everything we can to buy us enough time to
| innovate our way out of the problem, so yeah, tree planting ==
| good so long as the trees live long enough to do the job.
| jonas21 wrote:
| > _it is short term, at best._
|
| Short-term, where short-term is around 70 to 100 years [1],
| seems just fine to me. It'll buy us time to develop better
| technology for carbon sequestration and clean energy.
|
| In fact, the problem with planting trees might be the opposite
| -- trees don't reach their maximum rate of carbon sequestration
| for a couple of decades, and by then it might be too late.
|
| [1]
| https://www.fpl.fs.fed.us/documnts/pdf2011/fpl_2011_lippke00...
| samatman wrote:
| Properly managed agroforestry is an excellent carbon sink,
| where _properly managed_ is doing all of the heavy lifting
| here.
|
| The napkin strategy is to grow fast woods, kiln them into
| charcoal, spread some of it on the forest as a soil amendment,
| spread the rest on agricultural land, repeat.
|
| Elemental carbon weatherizes into CO2 very slowly, on the order
| of centuries, the half-life is more than a thousand years. So-
| called "biochar" (it's just charcoal) is an excellent soil
| amendment, mitigates topsoil depletion, supports good
| microbiomes, adsorbs fertilizers and releases them slowly, it's
| a big win. If we manage to do this on the necessary scale, we
| _might_ eventually hit the point where adding more char to soil
| isn 't worth it from an ecosystem health perspective, and then
| we can just put it into the various large holes we've dug into
| the earth to extract minerals. There is something very tidy
| about filling an old coal mine with synthetic coal!
| jonnycomputer wrote:
| Yes, back when I was doing archeology, we'd find pieces of
| charcoal 700-800 years old. And that was in the forests of
| Belize.
| xjlin0 wrote:
| Not sure about your definition of "short term" here. Where does
| the carbon in coal come from? The last time I read it's from
| the plants.
| jandrese wrote:
| The carbon in coal was previously sequestered underground and
| not part of the current carbon cycle. By burning all of that
| coal, oil, and natural gas we un-sequestered all of that
| carbon. So even if we replanted all of the forests there are
| still many gigatons of extra carbon in the atmosphere.
|
| It's "short term" because the plants will release the carbon
| back into the atmosphere in a few decades.
|
| So to combat climate change we need ways to sequester the
| carbon that will keep it out of the atmosphere permanently.
| There are no good solutions for this currently. Maybe at some
| point someone will figure out a way to economically create
| massive pure diamonds using CO2 from the atmosphere with
| renewable energy so we could use them as building materials
| or something. Thanks to the laws of thermodynamics we'll have
| to invest something like all of the energy we produced using
| fossil fuels to fix this problem. We can cheat a bit by going
| to a stable form instead of making it straight up crude oil
| again, but it's still an almost unfathomable amount of energy
| we're going to need. And our politicians still arguing if it
| is a good idea to stop digging the hole, and fighting tooth
| and nail against it. There are no jobs on a dead planet.
| njarboe wrote:
| Many species of trees live for hundreds of years, not
| decades.
| dragontamer wrote:
| > When it dies and rots, it will release that carbon again.
|
| What happens when a tree dies and turns into a house?
|
| > it is short term, at best.
|
| If the house stands for 100 years, then you've successfully
| sequestered said carbon for over 100 years (because only after
| then will the rotting process start). Even then, a lot of
| carbon turns into humus (which btw: we're also running out of
| Topsoil for our farms). So creating more carbon-rich humus as a
| topsoil replacement for our farms is ALSO a priority.
|
| Since humus is the final product of the rotting process, I'd
| argue that the carbon-content of humus represents the
| "permanently sequestered" bits of the carbon. Which IIRC, is
| still a substantial portion of the weight of the tree.
|
| There's also all the leaves that fell off the tree and turned
| into humus. Probably not as much by weight, but its quite
| possible that the leaves themselves allow the tree to sequester
| MORE than its weight in carbon.
| mannykannot wrote:
| True enough, but the situation currently is not one of
| expansion or even of a steady-state: old-growth forests are
| declining rapidly, and a good deal of the carbon they are
| squestering is being released over the short term. The issue
| with forests is their being reservoirs that are being emptied.
| theflyinghorse wrote:
| > tree planting == good
|
| In which cases is it not? Other than short term carbon sink we
| get more trees, wild life gets more trees allowing it to
| flourish, we get wood for building material, dead trees become
| soil.
| goodcanadian wrote:
| You are missing the context; I think suggesting tree planting
| as a serious method to combat climate change is absolutely
| harebrained. That does not mean I am against tree planting in
| principle. I agree with you and I am strongly in favour of
| rewilding for other reasons. Of course, that still means
| planting the right trees in the right places. Random planting
| of random trees is not likely to help much and may be a net
| negative if it gives people the feeling that they are doing
| something good when they aren't really.
| henearkr wrote:
| Maybe it just asks for being combined with a reasonably
| accurate accounting of the forest's carbon store at
| different points of time.
|
| This way, startups proposing forestry as a solution for
| carbon capture would be able to present accurate results
| and figures.
| henearkr wrote:
| Don't you leave out the thickening of trunks, and most
| importantly, carbon storage from fallen leaves of deciduous
| trees? Imho, the humus is also a compartment of the forest that
| stores carbon (even if it will be slowly transformed).
|
| Also, the decay of fallen trees is very slow, and is not 100%
| into carbon dioxide (the carbon will remain a very long time in
| the body of numerous plant and animal species), whereas the
| combustion for human use is complete and on a much smaller
| scale of time.
| jandrese wrote:
| The problem is that fallen leaves tend to decay in fairly
| short order. The total carbon capture is basically the
| current leaves plus one or two years of fallen leaves and
| that's it. The rest have returned most of their carbon to the
| atmosphere.
|
| And when you think about it, this makes sense. Trees aren't
| constantly burying themselves in their own leaves. The roots
| of trees stay about the same depth year after year, and
| they're not growing new root systems higher up the trunk.
| njarboe wrote:
| While I would guess that you are right for most trees, the
| Giant Sequoia redwood trees in California actually do bury
| themselves in their own pine needles. They can also grow
| roots out at a higher level, if needed. Of course they can
| live for thousands of years.
| henearkr wrote:
| It doesn't have to stay in the form of leaves. Only a
| fraction (maybe not tiny) really goes back to CO2, but a
| lot turns into other organisms, raw fiber, etc.
|
| So you argument would be: why then do trees not bury
| themselves in humus?
|
| I think that a fair part goes away with rain and water
| systems, and a small portion circulates in the form of
| mobile organisms.
| dbingham wrote:
| 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.
| BurningFrog wrote:
| > _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 wrote:
| Some soil accumulates. Other is washed out to lower areas
| of elevation. My guess is it's another thing that reaches
| steady state.
| goodcanadian wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| How do you feel about baking the timber in solar ovens
| first, before burying the charcoal, to go full _terra
| preta_?
| henearkr wrote:
| Just to precise, "tree-roting" is incredibly slow, and
| the tree mainly turns into other living forms (thus, also
| sequestered carbon) rather than in carbon dioxide (one
| part does, but far from 100%).
|
| It's like when you eat, you do not turn your food in pure
| gas, do you? And then the excreted/remaining mass will be
| buried etc (and will partly be turned into earthworms,
| nematodes, bacteria, moss, fungi, etc).
| saalweachter wrote:
| Hmmm, that's an interesting question.
|
| A person breaths out about 2.3 lbs of CO2 each day, which
| amounts to 0.6 lbs of carbon, all of which must have come
| from your food.
|
| Meanwhile, a person defecates about 1 lb per day, about
| 75% of which is water. Of the residue, about 25-50% of it
| is bacteria, and the remainder the undigested portion of
| your food. Bacteria is typically accounted 53% carbon;
| the undigested fats, carbohydrates and proteins will vary
| a lot in percentage, but is 40% carbon for carbohydrates,
| 50% for proteins, and "more" for fats.
|
| Which leaves a lot of variance, but something like 0.15
| lbs of carbon exiting at as a solid seems like a
| reasonable estimate.
|
| So the answer would be: you turn about 80% of the carbon
| in your food into CO2 gas.
| [deleted]
| henearkr wrote:
| That seems a lot, 80%.
|
| But after reading several times your calculation, it
| seems legit. Thanks.
|
| Then, as a conclusion, when you eat you delay 20% of your
| carbon footprint, and a fraction of these 20% may well be
| stored for a long duration (in sediments, or back into
| the food chain, etc).
|
| Then again, similarly, the fallen leaves of trees may
| store a fraction of their carbon for a long duration.
| elihu wrote:
| 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.
| User23 wrote:
| > It is sequestration, but it can take thousands of years
| for an inch of rich soil to accumulate in a 'steady
| state' system.
|
| And as anyone that's been to western England knows, it
| takes a single generation for it to all blow away and
| leave you with nothing but a barren heath that's good
| only for grazing sheep.
| goodcanadian wrote:
| Some will be sequestered in this way, but how much and
| under what conditions? Tropical rain forests, for
| example, are known to have very poor soils despite the
| massive amount of biomass growing in them. Almost
| everything is recycled back into the forest very quickly.
| Clearly, no significant accumulation of sequestered
| carbon is occurring there. On the other hand, peat bogs
| occur because dead plant matter falls into a low oxygen
| environment and doesn't really decay, so there can be a
| build up of sequestered carbon there, but that is rather
| specific conditions.
| craigbaker wrote:
| Some of the biomass is also washed away and becomes
| marine sediments, which can store a significant amount of
| carbon. https://cbmjournal.biomedcentral.com/articles/10.
| 1186/s13021...
| mturmon wrote:
| There are some debates in the comments involving process-based
| comparisons, e.g., when carbon release from decay outweighs
| carbon sinking from plant metabolism.
|
| It may be helpful to give this top-level summary from the
| National Climate Assessment [1]:
|
| "Net storage of atmospheric carbon by forests (742 teragrams, or
| Tg, of CO2 per year from 1990 to 2015) has offset approximately
| 11% of U.S. CO2 emissions. Assuming no policy intervention - and
| accounting for land-use change, management, disturbance, and
| forest aging - U.S. forests are projected to continue to store
| carbon but at declining rates (35% less than 2013 levels by 2037)
| as a result of both land use and lower CO2 uptake as forests grow
| older."
|
| [1] https://nca2018.globalchange.gov/chapter/6/ -> "Forest Carbon
| Dynamics"
|
| The NCA is your best one-stop-shop for the best current synthesis
| on such questions, unless you're literally publishing in this
| specific area (in this case, carbon cycle science at decadal
| timescales).
| omegant wrote:
| Genuine question, if old-growth forest do not work as carbon
| sinks, how all the petroleum we are extracting comes from? Is all
| from ancient marine environments?
| JamesBarney wrote:
| The article doesn't say old growth forests don't work as carbon
| sinks, just that don't work as well as they initially thought.
| black_puppydog wrote:
| Am I missing sth? I don't even see an abstract there, yet they
| want $8.99 for it?
| [deleted]
| sampo wrote:
| It's in the Matters Arising section of volume 591. These are
| short 1-3 page long contributions, shorter than research
| articles. And being so short, they don't have an abstract.
|
| Table of contents:
| https://www.nature.com/nature/volumes/591/issues/7851
|
| As of writing this comment, these short papers (this, and the
| counterargument, right after in the table of contents) don't
| seem to be in sci-hub. Until someone uploads them to sci-hub,
| they probably aren't available in the free web.
| black_puppydog wrote:
| Thanks for explaining. Didn't know that format. :)
| Kim_Bruning wrote:
| I remember reading about this decades ago. I guess it's still
| being discussed?
|
| Short summary of the theory:
|
| Trees are largely made of thin air ;-) : Carbon Dioxide provides
| the required (C)arbon, water that rains out of the air provides
| (H)ydrogen and (O)xygen, and (N)itrogen fixated from the air
| provides the basis for amino acids. This covers about 99% of the
| chemicals in the woody parts.
|
| Young trees want to grow a lot, so they make a lot of lignin and
| cellulose. These consist of C, H, and O. Once trees have grown
| tall enough, they tend to slow down, so you'd expect them to not
| grab as much carbon anymore.
| sp332 wrote:
| It says the original paper was published in 2008, and a reply
| was published last month.
| mykowebhn wrote:
| One correction, plants, including trees, don't get their
| nitrogen from the air, but from the soil.
| Kim_Bruning wrote:
| Technically correct, the best kind of correct!
|
| Of course, the way the nitrogen gets into the soil (as
| ammonia) is due to nitrogen fixing bacteria that do in fact
| get their nitrogen from the air. So the tree gets nitrogen
| from the air in a roundabout way.
|
| (Earth's atmosphere is 78% nitrogen, so as a bacterium you'd
| be a bit silly to ignore such a rich source)
|
| Same is true of Hydrogen and Oxygen of course, which fall as
| rain and enter the soil first, before being taken up by the
| roots.
| Qwertious wrote:
| True in basically all relevant cases but they recently found
| one type of mountain plant that pulls nitrogen from the air,
| which holds some promise for GM crops.
| Kim_Bruning wrote:
| There are actually a bunch of plants that can pull N2
| directly from air, by entering into a more direct symbiosis
| with nitrogen fixing bacteria in root nodules. (not
| typically trees though)
|
| Depending on where you live, you might even plausibly have
| some in your garden.
|
| https://en.wikipedia.org/wiki/Root_nodule
| bcbrown wrote:
| > Once trees have grown tall enough, they tend to slow down, so
| you'd expect them to not grab as much carbon anymore.
|
| I don't think that's accurate (or at least not very precise).
| Studies have shown that when evaluating the metric of annual
| addition of tree mass per acre in the rainforests of the
| Pacific Northwest, old-growth forests add as much or more when
| compared to "young" forests.
|
| I don't have any specific sources, but if you want to know more
| the research by Robert Van Pelt should be a good starting
| point.
| hcurtiss wrote:
| This is definitionally untrue. Forests have a maximum biomass
| carrying capacity, and they rarely reach that capacity,
| instead losing carbon to stochastic events like fire. Old
| growth forests "store" a lot of carbon, but their capacity to
| sequester is finite.
|
| https://www.fs.fed.us/psw/topics/fire_science/ecosystems/car.
| ..
| bcbrown wrote:
| You're not listening to what I'm saying. I'm not talking
| about carbon sequestration, I'm refuting the argument that
| "once trees have grown tall enough, they tend to slow
| down". Here, I pulled a source for you: https://citeseerx.i
| st.psu.edu/viewdoc/download?doi=10.1.1.45...
|
| > Wood production of the entire main trunk and whole crown
| both increased with size and age up to and including the
| largest and oldest trees we measured.
|
| This is even supported by your own link:
|
| > In the past, some researchers have suggested that
| converting old forests to young, fast-growing plantations,
| whose harvested wood products could store carbon for
| several decades, would create a net increase in long-term
| carbon stocks. This approach was based on the idea that old
| forests are slow growing and thus carbon sequestration
| slows down as forests age. _More recent research generally
| does not support this idea_ , as a global survey of old
| forests found that many continue to sequester carbon and
| have stocks that far exceed young, managed forests.
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