Land clearing generates coarse woody debris (CWD), much of which ultimately becomes atmospheric CO2. Schemes for greenhouse gas accounting must consider the contribution from land clearing, but the timing of the contribution will have large uncertainty, due to a paucity of knowledge about the rate of CWD disappearance. To better understand above-ground CWD disappearance following a land clearing event—through the actions of microorganisms, invertebrates, wildfire, or deliberate burning—we combined statistical modelling with an archive of semi-quantitative observations (units of CWD %), made within Queensland, Australia. Using a generalised additive mixed-effects model (median absolute error = 14.7%), we found that CWD disappearance was strongly influenced by the: (i) number of years elapsed since clearing; (ii) clearing method; (iii) bioregion (effectively a climate-by-tree species interaction); and (iv) the number of times burned. Years-since-clearing had a strongly non-linear effect on the rate of CWD disappearance. The data suggested that disappearance was reverse-sigmoidal, with little change in CWD apparent for the first three years after clearing. In typical conditions for Queensland, the model predicted that it will take 38 years for 95% of CWD to disappear, following a land clearing event; however, accounting for uncertainty in the data and model, this value could be as few as 5 years, or > 100 years. In contrast, due to an assumption about the propensity of land managers to burn CWD, the official method used to assess Australia’s greenhouse gas emissions predicted that 95% of CWD will disappear in < 1 year. In Queensland, the CWD generated by land clearing typically takes 38 years to disappear. This ultimately implies that a key assumption of Australia’s official greenhouse gas reporting—i.e. that 98% of CWD is burned soon after a clearing event—does not adequately account for delayed CO2 emissions.

中文翻译：

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模拟土地清理事件后粗木屑的消失

土地清理会产生粗木屑 (CWD)，其中大部分最终会变成大气中的二氧化碳。温室气体核算方案必须考虑土地清理的贡献，但由于缺乏对 CWD 消失率的了解，贡献的时间将具有很大的不确定性。为了更好地了解土地清理事件后地面 CWD 的消失——通过微生物、无脊椎动物、野火或故意燃烧的行为——我们将统计模型与昆士兰境内的半定量观察档案（单位为 CWD %）相结合， 澳大利亚。使用广义加性混合效应模型（中值绝对误差 = 14.7%），我们发现 CWD 消失受到以下因素的强烈影响：（i）自清除以来经过的年数；(ii) 清算方法；(iii) 生物区（实际上是气候与树种的相互作用）；(iv) 燃烧的次数。清除后的年数对 CWD 消失率具有很强的非线性影响。数据表明，消失呈反向 S 形，在清除后的前三年内 CWD 几乎没有明显变化。在昆士兰的典型条件下，该模型预测，在一次土地清理事件之后，95% 的 CWD 需要 38 年才能消失；然而，考虑到数据和模型中的不确定性，这个值可能只有 5 年，或 > 100 年。相比之下，由于对土地管理者燃烧 CWD 倾向的假设，用于评估澳大利亚温室气体排放的官方方法预测，95% 的 CWD 将在 < 1 年内消失。在昆士兰，土地清理产生的 CWD 通常需要 38 年才能消失。这最终意味着澳大利亚官方温室气体报告的一个关键假设——即 98% 的 CWD 在清除事件后很快被燃烧——并没有充分考虑延迟的 CO2 排放。