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

这项研究将探索8个热带森林中的树木对厄尔尼诺现象的反应。2015-16年的厄尔尼诺现象是自1950年以来最强的三次之一。强烈的厄尔尼诺现象给全球带来了气候异常，包括气温上升，云量减少，降雨量减少，热带大部分地区干旱。这项研究中的八个森林分布在从潮湿的加勒比海到巴拿马干燥的太平洋海岸的陡峭的降雨梯度上。该项目利用了以前绘制的每一片森林中的苗木和树木种群。尽管2015-16年的厄尔尼诺现象最初使树木受益，因为它减少了云层覆盖，增加了2015年雨季的光照能力，但旱季比正常情况下开始得更早，这可能意味着未来将出现严重的干旱。该项目将测试几个假设，即通常潮湿和干燥的森林中的树种如何对降雨量减少做出不同的反应。干旱和光照增加对苗木和成年树木健康的净影响将决定哪些物种再生，潜在地改变森林的长期构成。这个项目之所以重要，是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对厄尔尼诺事件的反应将有助于洞察森林将如何应对长期气候变化。在2016年厄尔尼诺事件期间，研究人员将调查巴拿马中部8个森林中现有的树木苗木小区网络，这些森林跨越明显的降雨梯度。人口普查将测量两个大小类别的苗木招募、生长和存活，并(1)确定哪些森林地点和树种受极端厄尔尼诺事件影响最大，(2)检查土壤水分供应减少和光照增加对苗木表现的相对作用，(3)评估苗木对厄尔尼诺现象反应的功能性状的预测价值，(4)测量与厄尔尼诺有关的苗木死亡率的大小分布，以及(5)通过评估最小土壤和叶水势及其在森林和物种之间的变化，为模拟极端厄尔尼诺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事件对热带森林更新影响的最全面的研究之一，将深入了解物种、苗木大小类别和森林内部和之间的反应差异。这项研究将改进对全球气候变化对这些森林影响的预测，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将是重要的。该项目还将通过提供研究基础设施和巴拿马相对较新的一组地块的数据，并通过收集各种物种的比较性能数据，促进巴拿马和其他热带地区未来的研究工作。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.