CSIRO Agriculture and CSIRO Land and Water, GPO Box 1700, ACT 2601, Australia.
CSIRO Agriculture and CSIRO Land and Water, Private Bag 10, Clayton South, VIC 3169, Australia.
Sci Total Environ. 2018 Feb 15;615:348-359. doi: 10.1016/j.scitotenv.2017.09.263. Epub 2017 Oct 2.
Reforestation of agricultural land with mixed-species environmental plantings of native trees and shrubs contributes to abatement of greenhouse gas emissions through sequestration of carbon, and to landscape remediation and biodiversity enhancement. Although accumulation of carbon in biomass is relatively well understood, less is known about associated changes in soil organic carbon (SOC) following different types of reforestation. Direct measurement of SOC may not be cost effective where rates of SOC sequestration are relatively small and/or highly spatially-variable, thereby requiring intensive sampling. Hence, our objective was to develop a verified modelling approach for determining changes in SOC to facilitate the inclusion of SOC in the carbon accounts of reforestation projects. We measured carbon stocks of biomass, litter and SOC (0-30cm) in 125 environmental plantings (often paired to adjacent agricultural sites), representing sites of varying productivity across the Australian continent. After constraining a carbon accounting model to observed measures of growth, allocation of biomass, and rates of litterfall and litter decomposition, the model was calibrated to maximise the efficiency of prediction of SOC and its fractions. Uncertainties in both measured and modelled results meant that efficiencies of prediction of SOC across the 125 contrasting plantings were only moderate, at 39-68%. Data-informed modelling nonetheless improved confidence in outputs from scenario analyses, confirming that: (i) reforestation on agricultural land highly depleted in SOC (i.e. previously under cropping) had the highest capacity to sequester SOC, particularly where rainfall was relatively high (>600mmyear), and; (ii) decreased planting width and increased stand density and the proportion of eucalypts enhanced rates of SOC sequestration. These results improve confidence in predictions of SOC following environmental reforestation under varying conditions. The calibrated model will be a useful tool for informing land managers and policy makers seeking to understand the dynamics of SOC following such reforestation.
将多种乡土树木和灌木混合作环境种植进行农业土地复垦有助于通过碳封存来减少温室气体排放，并有助于景观修复和生物多样性的增强。虽然生物量中碳的积累相对较为了解，但对于不同类型的造林后土壤有机碳（SOC）的相关变化却知之甚少。如果 SOC 封存率相对较小和/或高度空间变化，则直接测量 SOC 可能不具有成本效益，因此需要进行密集采样。因此，我们的目标是开发一种经过验证的建模方法来确定 SOC 的变化，以促进将 SOC 纳入造林项目的碳核算中。我们测量了 125 个环境种植区（通常与相邻农业区配对）的生物质、凋落物和 SOC（0-30cm）的碳储量，这些种植区代表了澳大利亚大陆不同生产力的地点。在将碳核算模型约束到观察到的生长、生物质分配、凋落物和凋落物分解的速率后，对模型进行了校准，以最大限度地提高 SOC 及其各部分的预测效率。由于测量和建模结果的不确定性，在 125 个对比种植区中，SOC 的预测效率仅为中等，为 39-68%。尽管如此，基于数据的建模仍提高了对情景分析输出的信心，证实了：（i）在 SOC 高度耗尽（即以前种植过作物）的农业土地上进行造林具有最高的 SOC 封存能力，特别是在降雨量相对较高（>600mmyear）的情况下；（ii）减少种植宽度、增加林分密度和桉树的比例可提高 SOC 封存率。这些结果提高了对不同条件下环境造林后 SOC 预测的信心。经过校准的模型将成为为希望了解此类造林后 SOC 动态的土地管理者和政策制定者提供有用的工具。
