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Carbon cycle

Post in 'The Green Room' started by Ehouse, Mar 14, 2013.

  1. Ehouse

    Ehouse Minister of Fire

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    I've been reviewing plant processes (photosynthesis, transpiration, respiration), to try to get an idea of the relative value of various types of vegetation cover in fixing carbon and releasing O2 etc. Two examples are ; Reforestation of abandoned farmland in New England, and slash and burn agriculture in the Amazon basin. Can anyone make a comparison, in such situations, between the conditions of mature forest, emerging new growth, and semi-permanent brush/scrub conditions?

    Ehouse

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  2. woodgeek

    woodgeek Minister of Fire

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    A very difficult problem. A big issue is soil carbon, which may (or may not) depending on the climate dwarf the amount of carbon above ground. And a lot of that is not settled among the scholars studying the issue. Indeed, such 'land use' contributions are a large part of the current uncertainty in the carbon footprint of our species, ethanol or food production, etc.

    If you want to fix carbon, plant a fast growing species and build the soil.
  3. Circus

    Circus Member

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    In the long run there's no difference co2 sequenching wise. I think you should plant a power plant, solar that is.
    What scares me is the permafrosted swamps up north and methane hydrate. Raising temperatures will rot the swamps and boil the hydrate. All that super greenhouse methane will boil the earth and then there will be nothing we can do about it.
  4. Ehouse

    Ehouse Minister of Fire

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    In the long run, yes, but what if we were to plant fast growing crop plants, as woodgeek says, to maximize carbon fixation, and use those crops for non food, non fuel uses, such as lumber and other building supplies which lock it up and delay it's release? I remember an insulating construction panel made from grass years ago, Agri-board or something like that. In stead of paying farmers not to produce, why not encourage them to raise such crops? Perhaps mixed timber plantations which practice selective clearcutting would fall under this category?
  5. dougstove

    dougstove Member

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    As woodgeek said, this is a complicated problem.
    i) The rate of accumulation of biomass.
    ii) That depends upon both the rate of photosynthesis, which is influenced by the species, and the local conditions, but also,
    iii) The countervailing respiration that releases CO2, both directly from the plant, and also from the dead plant material.
    iv) Respiratory breakdown of the dead material depends upon both the chemical composition of the material (lettuce leaves decompose faster than oak logs), but also the local conditions (leafs in North Carolina break down much faster than leaves in Labrador).
    v) The breakdown of the dead material determines the accumulation of carbon in the soil, which as woodgeek wrote, can be substantial.

    In terms of management, there is also the issue of the non-carbon inputs into biomass.
    One of the attractions of Switchgrass/Miscanthus as a possible biofuel or cellulose course is that the harvested mature grass contains little other than fixed carbon, so it does not drawn down the local soil nutrient stocks much.
    Brazilian sugarcane with nitrogen fixing symbionts is also good in that regard, in comparison to a heavy feeder like USA corn.

    In my area some of the soils are so poor that after 3-4 rounds of top-grading and then clear cutting, there may not be enough nutrient left in the soil to regenerate a full forest canopy. The nutrients were carried off in the wood.

    On top of all this, is the risk of releasing methane.
    Carbon for carbon, methane has about 24X the warming potential of CO2. So if 5% of the plant material is converted to methane that is released, that cancels the uptake of CO2 into the rest of the biomass.

    But in general, growing something, particularly perennials, is better than growing nothing.
  6. sesmith

    sesmith Member

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    Not sure exactly what you"re after cause it varies with forest age, stocking density and type, but here are some values for a couple of different ages and forest types:

    http://sustainability.tufts.edu/carbon-sequestration/

    You can look up the values for grass land. I don't remember if it's higher or lower than the forest values.
  7. sesmith

    sesmith Member

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  8. Ehouse

    Ehouse Minister of Fire

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    I had no agenda with the post, I knew woodgeek would zip out from under the dock and grab it, and with just a few replies I've increased my knowledge (hopefully others are going to school on it) a great deal!
  9. Ehouse

    Ehouse Minister of Fire

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    Looking at sesmith's chart, and seeing the huge relative amt. of sequestered carbon in swampland (as well as the methane), we have more to worry about than rising sea levels.
  10. Ehouse

    Ehouse Minister of Fire

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    Are there any non-fuel uses for Switchgrass or Miscanthus? Would simply plowing it under to store carbon in the soil be a good use on fallow (pay to grow nothing) farmland?
  11. dougstove

    dougstove Member

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    There are active research programs in this area. The cellulose content could be processed into paper or building products.
    As for plowing it under, it would probably be better to let the perennial grass or trees grow to accumulate soil carbon, in most habitats.

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