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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Understanding the effect of disturbance from selective felling on the carbon dynamics of amanaged woodland by combining observations with model predictions
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Understanding the effect of disturbance from selective felling on the carbon dynamics of amanaged woodland by combining observations with model predictions

机译：了解与模型预测的观测相结合的观察，了解干扰对氨化林地碳动力学的影响

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摘要

The response of forests and terrestrial ecosystems to disturbance is an important process in the global carbon cycle in the context of a changing climate. This study focuses on the effect of selective felling (thinning) at a managed forest site. Previous statistical analyses of eddy covariance data at the study site had found that disturbance from thinning resulted in no significant change to net ecosystem carbon uptake. In order to better understand the effect of thinning on carbon fluxes, we use the mathematical technique of four-dimensional variational data assimilation. Data assimilation provides a compelling alternative to more common statistical analyses of flux data as it allows for the combination of many different sources of data, with the physical constraints of a dynamical model, to find an improved estimate of the state of a system. We develop new observation operators to assimilate daytime and nighttime net ecosystem exchange observations with a daily time step model, increasing observations available by a factor of 4.25. Our results support previous analyses, with a predicted net ecosystem carbon uptake for the year 2015 of 426 ± 116 gCm~(-2) for the unthinned forest and 420 ± 78 gCm~(-2) for the thinned forest despite a model-predicted reduction in gross primary productivity of 337 gCm~(-2). We show that this is likely due to reduced ecosystem respiration postdisturbance compensating for a reduction in gross primary productivity. This supports the theory of an upper limit of forest net carbon uptake due to the magnitude of ecosystem respiration scaling with gross primary productivity. Plain Language Summary Forests play an important role in the global carbon cycle, removing large amounts of CO_2 from the atmosphere and thus helping to mitigate the effect of human-induced climate change. The response of forest ecosystem carbon dynamics to disturbance events (e.g., fire, felling, and insect outbreak) is not well understood. Many observations are currently made that give us insight into the processes occurring in forests; however, there are many processes that we cannot observe. Therefore, we must use mathematical models of forest carbon balance to better understand underlying behaviors; however, these models are often subject to large errors. In this study we use advanced mathematical techniques to combine information from both observations and model predictions of forest carbon balance, to improve current estimates and better understand the effect of disturbance from selective felling at a managed woodland. We find no significant change to the total forest carbon uptake after approximately 46% of trees are removed from the woodland. Our best modeled estimates suggest that this is due to photosynthesis being the main driver for ecosystem respiration, so that reducing the number of trees has reduced carbon uptake from photosynthesis but concurrently reduced respiration, meaning total carbon uptake is not significantly affected.
机译：森林和陆地生态系统的扰动的响应是在气候变化的上下文全球碳循环的重要过程。本研究的重点择伐（间伐）在管理森林立地的效果。在研究现场涡动相关数据的一次统计分析，已经发现，从细化扰动导致净生态系统碳吸收无显著变化。为了更好地了解间伐对碳通量的影响，我们利用四维变分同化的数学技术。数据同化提供了一个引人注目的替代通量数据的更常见的统计分析，因为它允许的数据的许多不同的来源的组合，具有动力学模型的物理约束，找到了系统的状态的改进估计。我们开发新的观测运营商吸收白天和每日时间步模型夜间净生态系统交换意见，4.25的系数增加可用的意见。我们的结果支持以前的分析，与预测的生态系统净碳吸收为426±116 GCM〜（-2）的未稀释的森林和420±78 GCM〜（-2），用于减薄的森林2015年尽管预测模型的降低337〜GCM的总初级生产力（-2）。我们表明，这很可能是由于减少了生态系统呼吸postdisturbance补偿毛初级生产力下降。此载体的森林的净碳吸收的上限理论由于生态系统呼吸缩放与总初级生产力的大小。平原语言总结森林在全球碳循环中起着重要的作用，从大气中大量CO_2的，从而帮助减轻人类引起的气候变化的影响。森林生态系统碳动力学扰动事件（例如，火，砍伐和昆虫爆发）的响应还不是很清楚。许多意见提出目前，让我们见识到森林中发生的过程;但是，也有很多过程，我们无法观察。因此，我们必须利用森林碳平衡的数学模型，以更好地了解潜在的行为;然而，这些模型往往会受到较大的误差。在这项研究中，我们采用先进的数学技术，信息来自观察和森林碳平衡的模型预测相结合，以改善目前的估计，并更好地理解扰动从择伐在管理林地的效果。我们发现在森林总碳吸收无显著变化后的树木约46％是从林地中删除。我们最好的模型的估计表明，这是由于光合作用是对生态系统呼吸的主要驱动力，因此，减少树木的数量已经减少碳吸收来自光合作用，但同时降低了呼吸，这意味着总碳吸收不显著影响。

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