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，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为改造的森林正在起火，危及世界上最大、生物多样性最多的热带雨林的未来，并可能成为进一步加剧区域和全球气候变化的反馈。在最近几年的干旱时期，巴西亚马逊地区的森林砍伐速度大大超过了火势。这些火灾导致大约一半的树木死亡，并使森林变得更容易受到后续火灾的影响。尽管亚马逊地区的野火日益盛行，但我们仍然非常有限的理解为什么这些低强度的林下火灾导致如此高的树木死亡率，哪些物种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，以及火灾发生后分类学和功能恢复的模式。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。这项工作将在巴西亚马逊东部Santarem的一个实地地点进行，我们在那里收集了几年来对一系列地块的详细植被生态和碳循环跟踪的测量结果。其中包括一些在2015/16年厄尔尼诺期间经历火灾的地块。我们将通过将最先进的森林燃烧实验与对一组独特的长期样地的持续监测相结合来实施这个项目，其中一些样地是我们通过2015-16年与强烈厄尔尼诺相关的野火事件进行跟踪的。考虑到我们已经建立的烧毁和未烧毁林地网络，我们与公园管理人员和联邦机构建立的牢固合作伙伴关系，以及我们可以用作基准信息的大量过去数据集，我们处于独特的地位来解决这些基本问题。火灾试验将涉及在有限的森林区域放火(在当地消防队的密切合作下)，跟踪火灾强度，并跟踪火灾现场个别树木的生理和死亡反应，包括根垫或树皮免受火灾损害的树木。我们还将试验不同的防火方法，以探索阻止此类火灾的最有效方法。通过密集的碳循环研究，我们将跟踪2015年火灾后长达七年的碳循环反应，使我们能够以新的视角了解更长期的碳循环反应以及火灾事件后生态系统的反应和恢复。除了促进关于人类世热带森林未来普遍存在且日益严重的威胁的科学知识，我们共同设计的影响路径确保我们还将提供信息并改进方法，以最大限度地减少因火灾导致亚马逊潮湿森林死亡的风险。我们将与当地消防管理人员密切合作，并与州和国家政策制定者接触，就如何管理森林保护区和森林-农业混合景观起草建议，以将火灾蔓延的风险降至最低。如果大规模应用，这些防火战略是一个重要的工具，可以帮助最大限度地减少亚马逊森林内因火灾而导致的大面积死亡的风险。

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.