RAPID: The effect of an extreme El Nino event on tropical forest seedling regeneration

这项研究将探索八个热带森林中的树木如何应对厄尔Niño事件。2015-16年厄尔尼诺Niño是自1950年以来最强的三次之一。强厄尔尼诺Niño事件导致全球气候异常，包括温度升高、云层减少、降雨量减少以及热带大部分地区的干旱。本研究中的8个森林分布在从潮湿的加勒比海到干燥的巴拿马太平洋沿岸的陡峭降雨梯度上。该项目利用了这些森林中以前绘制的幼苗和树木种群。尽管2015-16年厄尔尼诺现象Niño最初通过减少云量和增加2015年雨季的光照量而使树木受益，但旱季比正常情况下更早开始，这可能意味着未来将发生严重干旱。该项目将测试几种假设，即正常潮湿和干燥森林中的树种对降雨减少的反应不同。干旱和光照增加对幼苗和成年树健康的净影响将决定哪些树种能够再生，从而可能改变森林的长期构成。这个项目很重要，因为热带森林在全球碳和水循环中发挥着至关重要的作用，是地球上生物多样性最丰富的生态系统。此外，更深入地了解植物物种如何对El Niño事件做出反应，将有助于深入了解森林如何应对长期气候变化。在2016年El Niño事件期间，研究人员将调查巴拿马中部8个森林中现有的树苗地块网络，这些森林跨越了明显的降雨梯度。普查将测量两种大小类别的幼苗招募、生长和存活，并(1)确定哪些森林地点和树种受极端El Niño事件的影响最大，(2)检查土壤水分有效性降低和光照增加对幼苗性能的相对作用，(3)评估幼苗对El Niño响应的功能性状的预测价值，(4)测量El Niño-related幼苗死亡率的大小分布。(5)通过评估最小土壤和叶片水势及其在森林和物种间的变化，为模拟极端El Niño事件对热带森林的影响提供基线。该项目是迄今为止关于厄尔尼诺Niño事件对热带森林再生影响的最全面研究之一，并将深入了解物种内部和物种之间、幼苗大小类别和森林之间的反应变化。这项研究将改进对全球气候变化对这些森林的影响的预测，以及对植被-气候反馈的预测，这对当前和未来气候条件下的森林管理非常重要。该项目还将促进巴拿马和其他热带地区今后的研究工作，提供研究基础设施和来自巴拿马一组相对较新的地块的数据，并收集各种物种的比较表现数据。数据将在网上公开。

This research will explore how trees in eight tropical forests respond to an El Niño event. The 2015-16 El Niño is among the three strongest since 1950. Strong El Niño events bring climate anomalies worldwide, including increased temperatures, reduced cloud cover, decreased rainfall, and drought over a large portion of the Tropics. The eight forests in this study occur along a steep rainfall gradient from the wet Caribbean to the dry Pacific coast of Panama. The project capitalizes on previously mapped populations of seedlings and trees in each of these forests. Although the 2015-16 El Niño initially benefitted trees by reducing cloud cover and increasing light availability during the 2015 rainy season, the dry season began earlier than normal, which likely means a severe drought lies ahead. The project will test several hypotheses about how tree species in normally wet and dry forests respond differently to reduced rainfall. The net effect of drought and increased light on the health of seedlings and adult trees will determine which species regenerate, potentially altering long-term composition of the forests. This project is important because tropical forests play a vital role in global carbon and water cycles and are the most biologically diverse ecosystem on the planet. Also, a deeper understanding of how plant species respond to El Niño events will provide insight into how forests will respond to long-term climate change.During the 2016 El Niño event, researchers will survey an existing network of tree seedling plots within eight forests that span a pronounced rainfall gradient in central in Panama. Censuses will measure seedling recruitment, growth and survival across two size classes and (1) determine which forest sites and tree species are most affected by an extreme El Niño event, (2) examine the relative roles of reduced soil water availability and increased light on seedling performance, (3) evaluate the predictive value of functional traits for seedling responses to El Niño, (4) measure the size distribution of El Niño-related seedling mortality, and (5) provide a baseline for modeling the effects of extreme El Niño events on tropical forests through assessing minimum soil and leaf water potentials and their variation across forests and species. The project is among the most comprehensive studies of the effects of an El Niño event on tropical forest regeneration to date and will provide insight into variation of responses within and among species, seedling size classes, and forests. The research will improve projections for consequences of global climate change for these forests, as well as for vegetation-climate feedbacks, which will be important for forest management under current and future climate conditions. The project will also facilitate future research efforts both in Panama and in other tropical regions by providing research infrastructure and data from a relatively new set of plots in Panama and by gathering comparative performance data for a wide range of species. Data will be made publically available online.