The End of the Amazon Carbon Sink? (AMSINK)

森林如何应对气候变化和大气中二氧化碳浓度的增加影响着气候变化本身的进程。因此，这些生态系统的反应决定了人类需要在多大程度上减少温室气体排放，才能将全球变暖控制在商定的限度内。由于亚马逊对地球气候的巨大重要性，了解这些对亚马逊尤为关键。尽管迫切需要了解情况，但挑战是巨大的。卫星、飞机、实验和模型都有帮助，但在许多地点进行长期的逐树测量对于了解森林是如何加速或减缓气候变化速度至关重要的。到目前为止，保存完好的亚马逊森林提供了一个巨大的碳汇，减缓了气候变化。但十年前，已经有迹象表明，随着树木死亡率的上升，这种情况已经减弱，部分原因是严重的干旱。预测表明，水槽现在可能已经完工。如果是这样的话，我们在稳定地球气候方面失去了一个关键盟友。但自2011年以来，由于没有实地分析，知识和预测之间出现了巨大的鸿沟。这一预测是基于旧的测量数据，具有很大的不确定性，而且关键是没有考虑到森林的巨大自然变异性。AMSINK将解决这一问题。它使用雄心勃勃的新测量、分析和整合来发现南美森林如何以及为什么发生变化，它们在哪里以及为什么能够抵御气候变化，以及未来是什么。简而言之，理解这一关键系统的动态和命运。我们的中心思想是，生物质碳汇取决于森林的基本性质--气候、养分、土壤水分、物种和多样性以及周转率--因此在许多地方，碳的净吸收可能远远超过基于气候变化的简单预测。例如，虽然我们知道稀缺的养分限制了森林的生长，干旱会杀死树木，但(1)亚马逊地区三分之一的土壤相对肥沃，养分可能会长期生长，(2)多达一半的地区容易发生内涝，因此一些干燥可以通过使土壤通风而使树木受益，而(3)树木的抗旱性可能因物种而有很大不同。要了解S美国森林发生了什么，因此需要进行大规模、综合和雄心勃勃的测量工作。我们必须在很长一段时间内广泛观察许多森林。我们需要整体科学。要做到这一点，AMSINK需要三个关键步骤。首先，我们将联合15个森林小区网络，每个网络都研究热带S美洲地区不同的地点和变化方面，以创建一个跨越800万平方公里森林的相互连接的“团队”。其次，我们将通过在整个网络中进行可比较的营养、水分和物种干旱敏感度测量来丰富这些数据。第三，对于亚马逊最有价值的长期地块，我们将仔细、一致地逐个监测到2020年代中期。总体而言，AMSINK将把1000块地块整合到一个全球标准化的框架中，并在长达62年的时间里跟踪超过50万棵树。它将对这些进行分析，以发现到2026年生物质碳汇的分布、动态和趋势，确定其驱动因素，并检验我们关于森林抵御气候变化的假设。我们的新发现将被应用于预测该地区未来的增长、死亡和碳趋势，为国家政策制定者、全球协议和其他科学家提供关键的见解。总而言之，AMSINK首次在大陆范围内对自然如何控制热带森林的长期气候变化敏感性及其碳平衡进行了综合测量和分析。它用到2026年的新措施、对哪些汇过程正在改变的地方的新洞察、对原因的批判性理解以及对其未来如何展开的新限制来取代预测。它为英国纳税人的支持提供了非凡的科学价值，为政策制定者提供了重要的、及时的发现。

How forests respond to climate change and the increasing concentration of carbon dioxide in the atmosphere affects the course of climate change itself. The response of these ecosystems thus determine how much humanity needs to reduce greenhouse gas emissions to keep global heating within agreed limits. Understanding these is especially critical for the Amazon due to its huge importance for Earth's climate. While the need to know is urgent, the challenge is enormous. Satellites, planes, experiments and models all help, but long-term, tree-by-tree measurements in many sites are essential to understand how forests are accelerating or slowing the rate of climate change.So far intact Amazon forests have provided a huge 'sink' for carbon, slowing climate change. But a decade ago there were already signs this had weakened with tree death rates increasing, partly as a result of severe droughts. Projections suggest the sink may now be finished. If so we have lost a key ally in stabilising Earth's climate. But with no ground analysis since 2011 a big gap between knowledge and projection has opened up. The forecast is based on old measurements, has large uncertainty, and crucially fails to account for the huge natural variability of forests. AMSINK will resolve this. It uses ambitious new measurements, analysis and integration to discover how and why South American forests are changing, where and why they are able to resist climate change, and what the future holds. In short to understand the dynamics and destiny of this critical system.Our central idea is that the biomass carbon sink depends on the fundamental nature of forests - their climate, nutrients, soil water, species and diversity, and turnover rate - so that in many places net uptake of carbon may persist well beyond simple predictions based on climate-change. For example, while we know that scarce nutrients limit forest growth and droughts kill trees, (1) one third of the Amazon has relatively-rich soils where nutrients may allow long-term growth increases and (2) up to half is prone to waterlogging so some drying could benefit trees by aerating the soil, while (3) tree resistance to drought is likely to vary greatly with species.To know what is happening to S American forests, where and why therefore requires a huge, integrated and ambitious measurement effort. We must look widely at many forests for a long time. We need holistic science.To make this possible AMSINK takes three key steps. First we will unite 15 forest plot networks, each examining different locations and aspects of change across tropical S America, to create a connected 'team-of-teams' spanning 8 million km2 of forest. Second we will enrich these, with comparable nutrient, moisture and species drought-sensitivity measurements across the networks. Third, for the most valuable long-term Amazon plots we will take careful consistent tree-by-tree monitoring into the mid-2020s. In total AMSINK will integrate 1000 plots into a globally standardized framework and track more than half-a-million trees for up to 62 years. It will analyse these to discover the distribution, dynamics and trend of the biomass carbon sink to 2026, determine its drivers, and test our hypotheses of forest resistance to climate change. Our new findings will be applied to forecast future growth, mortality and carbon trends across the region, providing critical insights for national policy-makers, global agreements & fellow scientists.In all AMSINK makes the first continent-scale integrated measurement and analysis of how nature controls the long-term climate-change sensitivity of tropical forests and their carbon balance. It replaces projection with new measures to 2026, novel insight into which sink processes are changing where, critical understanding of why, and new constraints on how their future will unfold. It delivers exceptional scientific value for UK taxpayer support and vital, timely discoveries for policy-makers.