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Alternative stable states between subtropical forest and grassland: A palaeoecological case study in southern Brazil

亚热带森林和草原之间的替代稳定状态：巴西南部的古生态案例研究

基本信息

批准号：
299080296
负责人：
Professor Dr. Thomas Giesecke
金额：
--
依托单位：
Senckenberg Biodiversität und Klima Forschungszentrum (BiK-F)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/299080296?language=en
关键词：
Alternative stable states between subtropical

项目摘要

Forest and grassland are vastly contrasting terrestrial ecosystems that provide different ecosystem services. While frequent fires maintain grasslands, fires are suppressed by forests. Thus both systems are self-stabilizing and may occur under the same climate conditions. Large regions of the tropics and sub-tropics are climatically suitable for both ecosystems, and shifts between states may have consequences for regional and possibly global climate. Understanding the determinants of this bi-stability has recently received much attention, but has been mainly based on modern observations and model simulations. Palaeoecological techniques provide the opportunity to study the dynamics of state changes over longer time periods and thus contribute to the ongoing discussion. The natural vegetation in southern Brazil represents a mosaic of humid forests and grasslands, with forests expanding into the grasslands over the last 4000 years. This situation provides an ideal setting for a case study uncovering tipping points, determining factors of system resilience, as well as the dynamics of such a state shift. A number of pollen diagrams exist that describe this change, but are from small peat bogs with low sedimentation rate during the early and mid-Holocene, precluding detailed analysis of the process. The proposal aims to carry out a high resolution multi-proxy investigation on fire and vegetation dynamics from a 10 m Holocene sediment core of a small lake as a base for comparison with simulations from dynamic vegetation models. The timing of the forest expansion at different localities within the region provides additional information to understand the drivers and triggers of this vegetation shift, and the project aims to improve the dating of this change for already investigated sites and to provide additional local investigations. Grassland and forest species differ in pollen production and dispersal, and to reduce this bias and help in interpretation, an investigation will address the pollen-vegetation relationship. This will allow quantified estimates of the extent of grassland and its replacement by forest. The combined information will be used to test three competing hypotheses: a) Holocene precipitation increased gradually with a strengthened South American Monsoon, while forest expansion was limited by frequent fires and only occurred once a threshold was passed; b) a stepwise change in the precipitation regime triggered the rapid forest expansion; humans assisted in the spread of the Araucaria forest as the seeds have high nutritious value. A mechanistic vegetation model will be used for hypotheses testing, by forcing it with different climate scenarios and comparing the simulations against the quantitative vegetation reconstructions. Further data model experiments will be designed to test the current theory on alternative stable states between grasslands and forests.

森林和草地是截然不同的陆地生态系统，提供不同的生态系统服务。虽然频繁的火灾维持了草原，但森林抑制了火灾。因此，这两个系统都是自我稳定的，并且可以在相同的气候条件下发生。热带和亚热带的大片地区在气候上适合这两种生态系统，国家之间的转变可能会对区域乃至全球气候产生影响。理解这种双稳定性的决定因素最近受到了很大的关注，但主要是基于现代观测和模型模拟。古生态学技术提供了研究较长时期内状态变化动态的机会，从而有助于正在进行的讨论。巴西南部的自然植被代表了潮湿森林和草原的马赛克，在过去的4000年里，森林扩展到草原。这种情况为案例研究提供了理想的背景，揭示了临界点、系统复原力的决定因素以及这种状态转变的动态。一些花粉图存在，描述了这种变化，但从小泥炭沼泽与低沉积速率在全新世早期和中期，排除了详细的分析过程。该提案的目的是对一个小湖10米全新世沉积物芯的火灾和植被动态进行高分辨率多代理调查，作为与动态植被模型模拟进行比较的基础。该地区不同地点森林扩张的时间提供了更多信息，以了解这种植被变化的驱动因素和触发因素，该项目旨在改进已调查地点的这种变化的日期，并提供更多的当地调查。草地和森林物种在花粉产生和传播方面存在差异，为了减少这种偏差并有助于解释，调查将解决花粉-植被关系。这将使人们能够对草原的范围及其被森林取代的情况作出量化估计。结合的信息将被用来测试三个相互竞争的假设：a）全新世降水逐渐增加，加强南美季风，而森林扩张是有限的，频繁的火灾，只有发生在一个阈值被通过; B）逐步变化的降水制度引发了森林的快速扩张;人类协助南洋杉森林的蔓延，因为种子有很高的营养价值。将使用一个机械植被模型进行假设检验，方法是用不同的气候情景对该模型进行模拟，并将模拟结果与定量植被重建结果进行比较。将设计进一步的数据模型实验，以测试目前关于草原和森林之间的替代稳定状态的理论。