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Sometimes the wood at the bottom of our woodpile decays to the point where it has only a small fraction of its previous dry mass. What has happened to it? Where did all the carbon go? From the point of view of greenhouse gas emissions, is it better for the wood to be burned in my fire or for it all to rot back into the earth?

鈥� Dead wood is first converted into living biomass, mainly through the actions of fungi, other microbes and woodlice. Eventually, it ends up as carbon dioxide, methane, water and nitrogen, plus minor quantities of mineral solids, most of which eventually wash away or remain in the soil as fertiliser.

However, in terms of greenhouse gas emissions, rotting offers advantages despite its release of methane. Fire abruptly converts almost all the carbon into CO₂, whereas detritus feeders and agents of decay leave some combustible materials, such as lignin and humic acids, that act as buffer stores for carbon.

Those stores last for years, accumulating in the soil as solids rather than in the air as CO₂. It would take the CO₂ from burning a long time to settle down innocuously like the trapped residues produced by the wood rotting.

There is no simple global limit to how much carbon such storage could accumulate. Its only rivals for sheer magnitude would be the deep-sea accumulation of dissolved CO₂, and carbonate minerals and soils in places such as chalk cliffs and downs.

Jon Richfield, Somerset West, South Africa

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This article appeared in print under the headline 鈥淲aning woodpile鈥�