Evaluating fire-induced dieback of Amazonian rainforest

在亚马逊潮湿森林的许多地方，野火已经成为新的常态，这是一个没有与这种压力源共同进化的生态系统。大片以前未受干扰和人类改造的森林正在着火，危及世界上最大和最具生物多样性的热带雨林的未来，并可能作为一种反馈，进一步加剧区域和全球气候变化。在最近的干旱年份，巴西亚马逊地区的火灾范围大大超过了森林砍伐的速度。这些火灾导致大约一半的树木死亡，并打开了森林，使它们更容易受到后续火灾的影响。尽管亚马逊森林火灾越来越普遍，但我们对这些低强度的林下火灾为什么会导致如此高的树木死亡率，哪些物种的功能特征预测了这些火灾的脆弱性或存活率，野火对森林碳平衡的影响以及火灾事件后分类和功能恢复的模式仍然知之甚少。我们提出了一项研究计划，以在我们对这种野火影响的理解方面取得重大进展，包括导致短期和长期树木死亡的潜在机制。这项工作将在巴西东部亚马逊地区的Santarem的一个野外站点进行，我们在那里收集了几年来详细的植被生态和碳循环跟踪的测量结果。其中包括2015/16年厄尔尼诺Niño期间经历火灾的一些地块。我们将通过结合最先进的森林燃烧实验和对一组独特的长期采样地块的持续监测来实施该项目，其中一些我们已经跟踪了2015-16年与强厄尔尼诺Niño相关的野火事件。我们在解决这些基本问题方面处于独特的地位，因为我们已经建立了烧毁和未烧毁森林的网络，我们与公园管理人员和联邦机构建立了牢固的伙伴关系，我们可以使用大量过去的数据集作为基线信息。火灾实验将包括（在当地消防队的密切合作下）在有限的森林区域放火，跟踪火灾强度并跟踪火灾地块中个别树木的生理和死亡反应，包括树根或树皮不受火灾损害的树木。我们还将试验不同的防火隔断方法，以探索最有效的方法来阻止此类火灾。通过深入的碳循环研究，我们将追踪2015年火灾后长达7年的碳循环响应，为我们提供对火灾事件后长期碳循环响应和生态系统响应和恢复的新见解。除了推进关于人类世对热带森林未来的普遍和日益严重的威胁的科学知识外，我们共同设计的影响途径确保我们还将告知和改进方法，以尽量减少潮湿的亚马逊森林因火灾引起的枯死风险。我们将与当地消防管理者密切合作，并与州和国家政策制定者合作，起草关于如何管理森林保护区和林农混合景观的建议，以最大限度地降低火灾蔓延的风险。如果大规模应用，这些防火战略是一个至关重要的工具，可以帮助最大限度地减少亚马逊森林因火灾而大面积枯死的风险。

Wildfires have become the new norm in many parts of the Amazonian humid forest, an ecosystem that did not co-evolve with this stressor. Large areas of previously undisturbed and human-modified forests are catching fire, jeopardising the future of the largest and most biodiverse tropical rainforest in the world, and potentially acting as a feedback that would further increase regional and global climate change. In recent dry years the extent of fire has greatly exceeded the rate of deforestation in the Brazilian Amazon. These fires result in in about half of the trees dying, and open up the forests to make them more vulnerable to subsequent fires.Despite the growing prevalence of Amazonian wildfires, we still have a very limited understanding of why these low intensity understorey fires cause such high rates of tree mortality, which species functional traits predict vulnerability or survival to these fires, what are the impacts of wildfires on the forest carbon balance and what are the patterns of taxonomic and functional recovery following a fire event. We propose a research plan to achieve major advances in our understanding of such wildfire impacts, including of the underlying mechanisms that cause both short-term and longer-term tree mortality. This work will be based at a field site in Santarem in Eastern Brazilian Amazonia, where we have collected several years of measurements of detailed vegetation ecology and carbon cycle tracking over a range of plots. These include a number of plots which experienced fire during the 2015/16 El Niño.We will implement this project by combining a state-of-the-art forest burn experiment with continued monitoring of a unique set of long-term sampling plots, some of which we have tracked through the 2015-16 wildfire event associated with a strong El Niño. We are uniquely placed to address these fundamental questions given our network of burned and unburned forest plots that is already in place, the strong partnerships we have forged with park managers and federal agencies, and the numerous past datasets that we can use as baseline information. The fire experiment will involve setting fire to limited patch of forest (with the close cooperation of local fire brigades), tracking fire intensity and tracking the physiology and mortality responses of individual trees in the fire plots, including trees that have their root mats or their bark insulated from fire damage. We will also experiment with different fire break methodologies to explore the most effective way to stop such fires. With the intensive carbon cycle studies we will track the carbon cycle responses for up to seven years after the 2015 fires, giving us novel insight into the longer term carbon cycle responses and the ecosystem responses and recovery after a fire event.As well as advancing scientific knowledge about a pervasive and increasing threat to the future of tropical forests in the Anthropocene, our co-designed pathways to impact ensures we will also inform and improve approaches to minimise risk of fire-induced dieback of humid Amazonian forests. We will work closely with local fire managers, and engage with state and national policymakers, to draft recommendations on how to manage forest reserves and forest-agriculture mixed landscapes to minimise the risk of fire spread. If applied at a large scale, these fire prevention strategies are a crucial tool that can help minimise the risk of extensive fire-induced dieback within Amazonian forests.