Tropical forests responses to a changing climate: a quest at the interface between trait-based ecology, forest dynamics and remote sensing

当今生态学和生态系统科学中最紧迫的问题集中在生物群落如何应对全球环境变化。气候变化如何影响生物多样性？生物多样性如何影响生态系统对气候变化的适应能力？就地球系统科学而言，我们需要了解和模拟陆地生物圈将如何对大气变化做出反应（并且已经在做出反应），以及是否存在危险的阈值或“引爆点”，超过这些阈值或“引爆点”，主要生物群落可能无法恢复。在物种丰富的热带森林和木质稀树草原生物群落中，这一挑战最为紧迫和艰巨，它们共同拥有全球50%以上的多样性和60%以上的陆地生产力2。已经有越来越多的证据表明，大气变化正在对热带森林的生产力和树木组成产生影响。这种响应可能包括生产力的提高（可能是由于二氧化碳的增加）和/或退化或枯死，这可能是由于季节性增加和极端干旱事件的频率增加造成的，例如2005年和2010年亚马逊经历的两次“百年一遇”干旱，以及2015年影响全球许多热带地区的El Niño-associated强烈干旱。然而，目前的生态系统模型方法无法充分理解或模拟这种响应，因为它们无法捕捉到物种丰富的热带地区植物生态系统功能的高多样性和准连续性质。忽视功能性生物多样性会大大简化和过度敏感生态系统对环境干扰的模拟响应。我们面临的一些关键挑战围绕着如何跟踪热带生态系统的物种组成和功能的变化，因为它们对全球变化做出了反应。通过将热带生物多样性简化为功能变异的几个关键轴，利用植物功能性状提供了一条潜在的前进道路。该项目将首次对完整热带森林和木本稀树草原的长期功能变化进行分析。首先，通过将热带地区长期森林清查数据形式与新收集和整理的热带树木功能性状数据相结合，探索树木群落及其功能特征在气候变化下如何随时间变化。它还将研究不同生物气候区域（包括不同海拔、纬度和气候条件）的特征变化模式如何变化，以更深入地了解土壤和过去的气候变化如何影响当前对气候变化的敏感性。接下来，它将研究生态系统物种组成的相关变化是否足够快，以跟上观测到的气候变化速度。最后，它将通过使用来自欧洲航天局哨兵-2哥白尼任务的最新一代卫星多光谱数据，探索大规模监测特征模式的潜力。该项目将在以下方面带来一个阶段性的变化：1)我们对气候变化如何驱动性状分布的理解；2)我们通过遥感预测功能性状组成的能力；3)将影响我们跟踪国际政策进展的方式，并为这些政策提供信息，如爱知生物多样性目标（目标a和C）、可持续发展目标（应对气候变化及其影响）、生物多样性和生态系统服务政府间科学政策平台（IPBES）和iv)将促进从描述性特征生态学向更具预测性特征生态学的过渡。

The most pressing questions in ecology and ecosystems science today focus on how communities of organisms respond to global environmental changes. How is biodiversity affected by climate change? And, how does biodiversity influence ecosystem resilience to climate change? In terms of Earth system science, we need to understand and model how the terrestrial biosphere will respond (and already is responding) to atmospheric change, and whether there are dangerous thresholds or "tipping points" beyond which major biomes may not be able to recover.Nowhere is the challenge more urgent or more daunting than in the species-rich tropical forest and woody savanna biomes, which together are home to more than 50% of global diversity and over 60% of terrestrial productivity2. There is already mounting evidence that atmospheric change is having an effect on tropical forest productivity and tree composition3. This response may include a stimulation of productivity (caused perhaps through rising CO2), and/ or a degradation or dieback, caused perhaps by increased seasonality and increased frequency of extreme drought events, such as the two "once-a-century" droughts experienced by Amazonia in 2005 and 2010, and the intense El Niño-associated drought of 2015 that affected many tropical regions worldwide. However, we cannot adequately understand or simulate such responses with current ecosystem model approaches that cannot capture the high diversity and the quasi-continuum nature of plant ecosystem function in the species-rich tropics. Neglect of functional biodiversity can greatly oversimplify and over-sensitise the simulated response of an ecosystem to an environmental disturbance. Some of the key challenges we face revolve around how can we track changes in the species composition and function of tropical ecosystems as they respond to global change. The use of plant functional traits provides a potential way forward by simplifying tropical biodiversity into a few key axes of functional variation. This project will conduct the first analysis of long term functional change in intact tropical forests and woody savannas. Firstly, it will explore how tree communities and their functional characteristics have shifted over time under a changing climate, by combining long-term forest inventory data form across the tropics with newly collected and collated data on tropical tree functional traits. It will also examine how the patterns of traits shifts vary across bioclimatic regions, which encompass different elevation, latitude and climatic conditions, to gain greater insight into how soils and past climate variation influence current sensitivity to climate change. Next it will examine whether the associated shifts in ecosystem species composition are sufficiently rapid to keep pace with the observed rates of climate change. Finally, it will explore the potential of monitor trait patterns at scale through the use of the newest generation of satellite multispectral data from the European Space Agency Sentinel-2 Copernicus mission.This project will bring a step-change in i) our understanding of how climatic changes drive traits distributions, ii) our ability to predict functional trait composition by remote sensing, iii) will impact the way how we track the progress towards, an inform sections of, international policy such as the Aichi Biodiversity Targets (Goal A and C), Sustainable Development Goals (combating climate change and its impacts), the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) and iv) will foster a transition from a descriptive to a more predictive trait ecology.