在合理可靠的生物多样性科学中建立“基于自然的气候方案”

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摘要

Abstract

目前气候政策中对造林的片面关注存在风险，一是会降低长期碳储存和人类适应力，二是会威胁人类保护生物多样性所作的努力。重点关注生物多样化和完整的自然生态系统，而不是快速生长型造林，将有助于各国实现《巴黎协定》的目标并受益更多。

The current narrow focus on afforestation in climate policy runs the risk of compromising long-term carbon storage, human adaptation and efforts to preserve biodiversity. An emphasis on diverse, intact natural ecosystems - as opposed to fast-growing tree plantations - will help nations to deliver Paris Agreement goals and much more.

作者：Nathalie Seddon, Beth Turner, Pam Berry, Alexandre Chausson and Cécile A. J. Girardin

自然生态系统可以帮助我们对抗气候变化的驱动因素和影响，这一观点在过去几年里得到了越来越多的支持，包括在最近出版的IPCC特别报告中也强调了这一观点¹。尤其是关于气候变化的《巴黎协定》呼吁各方承认“确保所有生态系统（包括海洋）完整和保护地球母亲类似文化中所存在的生物多样性的重要性”，其中66%的协议签署国在其气候宣言中对“绿色”或“基于自然的解决方案”作出了承诺（框1）。

The idea that natural ecosystems can help us fight both the drivers and impacts of climate change has been gaining traction over the past few years, including recent emphasis in the IPCC Special Report¹. In particular, the Paris Agreement on climate change calls on all parties to acknowledge 'the importance of ensuring the integrity of all ecosystems, including oceans, and the protection of biodiversity, recognized by some cultures as Mother Earth', and 66% of signatories to the agreement commit to 'green' or 'nature-based solutions' in their climate pledges (see Nature-Based Solutions Policy Platform) (Box 1).

对自然价值的认识，特别是通过将森林作为碳汇的政策，是谈判人员和非国家参与者来之不易的成果，并具有至关重要的意义。然而，我们也关心政策制定者所收到的陈述所涉及的方面，并呼吁研究生物多样性和生态系统功能和服务的科学家充分参与并了解将高层承诺转化为实际行动的这一过程。

Such recognition ofnature's value - in particular through policies promoting forests as carbon sinks - was hard-won by negotiators and non-state actors and is vitally important. However, we are concerned by aspects of the narrative reaching policymakers, and call on scientists studying biodiversity and ecosystem functions and services to fully engage with and inform the process by which high-level pledges are translated into on-the-ground actions.

关注森林

A Focus on Forests

对自然的高级别多边承诺目前的重点是森林。波恩挑战 （The Bonn Challenge）由世界自然保护联盟 （IUCN）和德国于2011年发起，目前有56个国家参与，旨在通过全球的努力到2020年恢复1.5亿公顷被砍伐和退化的森林，2030年恢复3.5亿公顷²；2014年，37个国家政府、63个非政府组织、53家跨国公司和16个原住民团体签署了《纽约森林宣言》（New York Declaration on Forests），承诺到2020年将森林砍伐量减半，到2030年彻底停止森林砍伐；同时，一项新的25年计划，《万亿棵树伙伴关系》（Trillion Trees Partnership）希望到2050年恢复1万亿棵树，这一数字是扭转全球树木覆盖率下降所需的数量。这些倡议已促使大量私营公司自愿承诺从其供应链上，消除森林砍伐。此外，可持续发展目标 （Sustainable Development Goals, SDGs）的签署国承诺到2020年停止砍伐森林，联合国里约《生物多样性公约》（United Nations Rio Convention on Biological Diversity） 也在生物多样性和增加碳储量方面提出了毁林问题。

When it comes to high-level multilateral pledges for nature, the current focus is on forests. The Bonn Challenge - launched by the International Union for Conservation of Nature (IUCN) and Germany in 2011 and currently involving 56 nations - is a global effort to restore 150 million hectares of deforested and degraded land by 2020 and 350 million hectares by 2030²; the New York Declaration on Forests - signed in 2014 by 37 governments, 63 non-governmental organizations, 53 multinational companies and 16 indigenous community groups - pledges to halve deforestation by 2020 and end it by 2030; and the Trillion Trees Partnership is a new 25-year initiative to restore onetrillion trees by 2050, the number needed to reverse the global decline in treecover. Such initiatives have inspired a significant number of private companies to voluntarily commit to eradicating deforestation from their supply chain. Added to this, signatories to the Sustainable Development Goals have committed to stop deforestation by 2020, and the United Nations (UN) Rio Convention on Biological Diversity also addresses deforestation, both in terms of biodiversity and enhancement of carbon stocks.

从气候角度来看，这种对森林的关注至关重要。2007 - 2016年，全球土地利用变化（主要是毁林）产生的二氧化碳排放量约占全球排放量的12%，而同期陆地碳汇储存的二氧化碳约占全球排放量的28%（每年3.0 ± 0.8GtC）³。到2030年，3.5亿公顷恢复的森林（即波恩挑战）将每年多储存1.6亿吨二氧化碳，相当于全球碳排放量14%²。由于森林既是二氧化碳的来源源又是碳汇，长期以来，森林在国际气候变化政策中都发挥着关键作用（框2），并日益受到关注。

From a climate perspective, this focus on forests is vitally important. Global CO2emissions from land-use change (mainly deforestation) represented around 12% of global emissions for 2007–2016, while the terrestrial carbon sink stored around 28% of emissions (3.0± 0.8 GtC per year) over the same period³. The restoration of 350 million hectares of forest by 2030 (that is, the Bonn Challenge) would add to this, sequestering up to 1.6 GtC per year, equivalent to 14% of the global carbon emissions². Because of this powerful role as both a source and a sink for CO2, forests have long played a key role in international climate change policy (Box 2) and are increasingly in the limelight.

单一栽培的问题

The Problem with Monocultures

目前的问题是这些对森林的高层承诺如何转化为实际行动。现有的国际框架仅为评估森林碳储量提供了一个对森林的定义，结果造成承诺往往更关注森林的面积而非保护森林和造林的质量（见Nature-based Solutions Policy platform 和引文⁴ ）。这一做法存在问题，尤其因为完整的森林预计会比退化的森林储存更多的碳⁵。此外，这一方式鼓励建立由快速生长物种组成的单一栽培种植园，包括外来物种。尽管这些种植园可能可以在短期内储存碳，但由于气候变化导致的环境变化和干扰越来越迅速、越来越严重⁷，这些种植园长期储存碳的能力也会被削弱⁶。

The issue is how these high-level pledges for forests translate into action on the ground. Existing international frameworks provide a definition of forests created for the purpose of assessing forest carbon stocks alone and as a result pledges tend to focus more on the extent rather than the quality of forest to be protected, afforested or reforested (see Nature-Based Solutions Policy Platform and ref.⁴).This is problematic not least because intact forests have been estimated to hold more carbon than degraded forests⁵. Furthermore, the approach encourages the establishment of monoculture plantations of fast-growing species, including exotics. Although such plantations may store carbon in the short term, their capacity to do so over the long term is impaired by changing conditions and disturbances⁶  that are becoming more rapid and severe under climate change⁷.

森林要长期固碳，就必须能够抵御、恢复或适应这些变化⁷。越来越多的证据表明，这种功能性恢复力是由如生态系统的连通性、异质性和多个生态层次的多样性等因素强烈决定的⁸。例如最近实验研究表明，与单一栽培相比，热带森林的多样化人工林更能抵御干湿极端气候⁹，混交林更能抵御害虫和疾病¹⁰。 人们还普遍认为，在面对环境变化时，连通性对完整的森林及其生物群的适应能力和完整性至关重要¹¹。

For forests to sequester carbon long term, they must be able to resist, recover or adapt to these changes⁷, and there is growing evidence that such functional resilience is strongly determined by factors such as ecosystem connectivity, heterogeneity and diversity at multiple ecological levels⁸. For example, recent experimental studies demonstrate that compared to monocultures, diverse plantations of tropical forest are more resilient to wet and dry climate extremes⁹, and mixed-species forests are more resistant to pests and disease¹⁰. Connectivity, mean while, is widely viewed as being critical to the adaptive capacity and integrity of intact forests and their biota in the face of environmental change¹¹.

因此，为了实现长期的碳储存的减缓潜力，政策必须从鼓励单一物种种植转向支持可增强功能性恢复力的生态属性的做法。这些政策将更符合最近的证据，即面对气候变化，（物种和性状的）多样性是保护森林碳汇的关键¹²。

Therefore, to enable long-term carbon storage mitigation, policy must move away from encouraging single-species plantations and instead support practices that enhance the ecological attributes that underpin functional resilience. Such policies would be more in line with recent evidence that diversity (of species and traits) is key to preserving forest carbon sinks in the face of climate change¹².

其他生态系统呢？

What about the rest?

当前对森林的重视不能削弱其他生态系统是至关重要的，因为它们其中也有许多在碳储存方面非常重要。一个新的旨在提高应对气候变化的自然方案知名度的活动主张：恢复和保护森林可以“提供30%到2030年所需的气候解决方案”。虽然这一宣传活动着重强调了森林，但它基于的研究指出，更好的管理所有主要自然陆生生境，包括草原、湿地和农田，可以提供2030年所需二氧化碳减排量的37%，并有超过66%的机会将全球变暖幅度控制于2°C以内 （ref.¹³）。

It is vital that the current emphasis on forests does not detract from other ecosystems, many of which are also very important for storing carbon. A new campaign to raise the profile of natural solutions to climate change advocates that restoring and protecting forest can 'deliver 30% of the climate solution needed by 2030'. Although the campaign strongly emphasizes forests, it is based on a study showing that better stewardship or management in all major natural terrestrial habitats, including grasslands, wetlands and agricultural lands, could help to provide up to 37% of the CO₂ mitigation needed through to 2030 for a greater than 66% chance of keeping warming to less than 2 °C (ref. ¹³).

特别是红树林，是地球上最有效的碳库之一，其平均长期碳掩埋率（即有机碳在沉积物中积累的速率）是其他陆地生态系统（包括北方森林和热带森林）的45倍以上¹⁴。泥炭地也拥有巨大的碳储量（占世界碳储量的25%），但只覆盖了2-3%的陆地面积¹⁵。

Mangroves, in particular, are one of the planet’s most efficient carbon storehouses, with mean long-term carbon burial rates (that is, rates at which organic carbon accumulate in sediments) more than 45 times greater than any other terrestrial ecosystem, including boreal and tropical forests¹⁴. Peatlands also hold vast reservoirs of carbon (25% of world's carbon) but cover only 2–3% of terrestrial areas¹⁵.

同时，天然草地在土壤中也储存了大量的碳，并且比森林更能抵御干旱和野火，从长远来看是更可靠的碳汇¹⁶。然而，这些重要的碳储备在气候变化政策中几乎没有出现。

Meanwhile, natural grasslands harbor substantial carbon stores within their soil and can be more resilient than forests to drought and wildfires, making them a more reliable carbon sink in the long term¹⁶. However, these important carbon stores barely feature in climate change policy.

例如，虽然42%的《巴黎协定》签署国将造林和/或恢复陆地森林列入其国家自主贡献（Nationally Determined Contributions, NDCs） 计划的减缓部分，但只有19%有海岸线的签署国对沿海生境采取了同样的措施。此外，草原只在8%的NDCs中出现过，而山地栖息地更是只在4%的NDCs中出现（参考Nature-Based Solutions Policy Platform）同时，一些重要的、自然无树生境正受到造林的威胁。这尤其令人不安，因为原来的栖息地往往能提供更多、更有适应力的碳储存效益¹⁷。

For example, while 42% of signatories to the Paris Agreement include afforestation and/or restoration in terrestrial forest in the mitigation components of their nationally determined contributions (NDCs), only 19% of signatories with coastlines do the same for coastal habitats. Meanwhile, grasslands appear in only 8% of NDCs, and for montane habitats, in only 4% (see Nature-Based Solutions Policy). Moreover, some of these important, naturally treeless habitats are threatened by afforestation, which is particularly troubling given that the original habitat can often provide greater and more resilient carbon storage benefits¹⁷.

换句话说，我们不能以继续破坏或取代其他至关重要的生态系统为代价来优先化森林。为了实现这一平衡，在讨论基于自然的解决方案 (nature-based solutions, NbS) 对气候变化的重要性以及鼓励政策决策者考虑这些解决方案时，有必要更具包容性。

In other words, forests must not be prioritized at the cost of continuing to destroy or replace other vitally important ecosystems. To achieve this balance there is a need to be more inclusive when discussing the importance of nature-based solutions to climate change and when encouraging policymakers to take them into account.

多样性是人类适应的关键

Diversity is key for human adaptation

在利用自然生态系统减缓气候变暖的努力中，同样重要的是不能忽视它们在支持人类适应气候变化方面的重要作用。除了确保可靠的减缓服务外，优先化各种各样的生态系统并促进它们的功能性适应力，还可确保一系列对适应气候变化至关重要的生态系统服务¹⁸。

In the drive to harness natural ecosystems to slow warming, it is also important not to lose sight of their essential role in supporting human adaptation to climate change. Prioritizing a variety of ecosystems and promoting their functional resilience will also secure a suite of ecosystem services vital for adaptation¹⁸, in addition to ensuring reliable mitigation services.

流域内的自然生境可以保障和调节供水，并保护社区免受洪水和土壤侵蚀；红树林、暗礁和盐碱滩可以抵御风暴潮和海岸侵蚀；农林复合（即在作物之间植树或在森林内种植作物）可以在更干燥、变化更大的气候条件下保持和提高产量¹⁹。

Natural habitats in watersheds can secure and regulate water supplies and protect communities from flooding and soil erosion; mangroves, reefs and salt marshes offer protection from storm surges and coastal erosion; and agroforestry (planting trees among crops or crops within forest) can maintain and enhance yields in drier, more variable climates¹⁹.

此外，通过避免气候变化相关灾害的损失，这些基于自然的适应解决方案也具有许多经济效益。例如，美国东北部的沿海湿地每年预计可提供232亿美元的风暴保护服务²⁰，而在没有珊瑚礁的情况下，每年洪水造成的损失将增加一倍，全球频繁的风暴造成的损失将增加两倍²¹。

Moreover, there are many economic benefits of these nature-based adaptation solutions through avoided losses to climate change related disasters. For example, coastal wetlands in the northeast of the United States are estimated to provide US$23.2 billion per year in storm protection services²⁰, while in the absence of reefs, annual damages from flooding would double and costs from frequent storms would triple globally²¹.

换句话说，恢复和保护自然不仅仅是为了储存碳和减缓气候变暖，它还涉及到对生态系统符合成本效益的保护，以帮助我们抵御洪水、干旱、山体滑坡、风暴、热浪、火灾和其他在气候变化下日益常见的灾难。最终，这些解决方案主要是与自然的合作，使生态系统在面对变化时继续支持人类发展和人类福祉（框1）

In other words, restoring and protecting nature really isn't just about storing carbon and slowing warming, it's also about cost-effective protection of ecosystems to help shield us from floods, droughts, landslides, storms, heatwaves, fire and other disasters increasingly common under climate change. Ultimately, it is about working with nature in such a way that ecosystems continue supporting human development and well-being in the face of change (Box 1).

结合生物多样性和气候变化

Biodiversity and climate change integration

所有这些都强调了，生态系统科学家、研究人类适应力和恢复力的社会科学家，以及那些设计和实施气候变化政策的科学家之间，需要建立更加牢固的联系。虽然对各级生物多样性（包括生境多样性）在减缓和适应气候变化方面所能发挥的作用的了解正在迅速增长，但气候变化和生物多样性的政策制定和执行在很大程度上仍然是分开的。

All this highlights the need for much stronger links between ecosystem scientists, social scientists studying human adaptation and resilience, and those designing and implementing climate change policy. While the understanding of the role that biodiversity at all levels, including a diversity of habitats, can play in mitigating and adapting to climate change is growing rapidly, policy development and implementation for climate change and biodiversity remain largely separate.

其结果是，在要种植或恢复的森林区域外，气候承诺缺乏强有力的针对自然的目标。随着气候承诺的修订，将这方面的知识融入这一修订过程，并帮助提高对自然的雄心非常重要。这一综合解决方法的实施已初见成效。

The result is a lack of robust targets for nature in climate pledges, beyond areas of forest to be planted or restored. As climate pledges get revised, it is important that this knowledge is informing the process and helps raise ambition for nature. Examples of what can be achieved through this integrated approach are already emerging.

生物多样性是气候解决方案的核心

Biodiversity at the heart of climate solutions

2018年底，在由加州州长Jerry Brown发起的全球气候行动峰会 （Global Climate Action Summit） 和联合国里约大会上，基于自然的解决方案（NbS）分别都受到了关注。在全球气候行动峰会的背景下，NbS被确定为2019年9月联合国气候变化行动峰会的六项行动计划之一。同时，联合国《生物多样性公约》第十四届缔约方会议正式决定将气候变化问题纳入国家生物多样性战略，反之亦然²²。

Nature-based solutions were in the limelight towards the end of 2018 at the Global Climate Action Summit instigated by California governor Jerry Brown, as well as both UN Rio Convention Conferences. On the back of the Global Climate Action Summit, nature-based solutions were identified as one of six action portfolios for the UN Climate Change Summit in September 2019. Meanwhile, the UN Convention for Biological Diversity at its 14th Conference of the Parties formally decided to integrate climate change issues into national biodiversity strategies and vice versa²².

在全球变暖的背景下，人们对大自然重要性的认识正迅速增长，这一点值得庆祝。然而，在与自然有关的议程转化为行动时，多样化且完整的自然生态系统的重要性也决不能被忘记。在应对气候变化的斗争中，森林是绝佳的盟友。但是，除非我们以科学为指导，通过当地管理实施，恢复和保护多种多样、物种丰富、且有恢复力的生态系统，我们将不可能赢得这场战斗。

This rapidly growing recognition of nature’s importance in a warming world is to be celebrated. However, as agendas for nature get translated into actions, the importance of diverse, intact natural ecosystems must not be forgotten. In the fight against climate change, forests make excellent allies. However, unless a diversity of species-rich resilient ecosystems are restored and protected — guided by science and implemented through local stewardship — the battle cannot be won.

我们希望，在12月将于波兰举行的联合国《气候变化框架公约》（UNFCCC）会议的到来之际，倡导采取行动并提供资金的国家可以铭记这一点。

We hope that those advocating for action and funding in the wake of the UN Framework Convention on Climate Change (UNFCCC) meeting in Poland in December will bear this in mind.

参考文献

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原文链接：

https://www.researchgate.net/publication/330691577_Grounding_nature-based_climate_solutions_in_sound_biodiversity_science