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.

森林和草原是提供不同生态系统服务的陆地生态系统。虽然频繁的大火维持草原，但火灾被森林抑制。因此，这两个系统都是自动稳定的，并且可能在相同的气候条件下发生。热带地区和亚热带的大区域在气候上适合两个生态系统，国家之间的转变可能会对地区和可能的全球气候产生影响。了解这种双重稳定性的决定因素最近受到了很多关注，但主要基于现代观察和模型模拟。古生态技术为研究状态变化的时间变化提供了机会，从而有助于持续的讨论。巴西南部的自然植被代表着潮湿的森林和草原的马赛克，在过去的4000年中，森林膨胀到草原上。这种情况为案例研究提供了理想的设置，可以揭示临界点，确定系统弹性的因素以及这种状态转移的动态。存在许多描述这一变化的花粉图，但来自早期和中新世期间沉积速率低的小泥炭沼泽，排除了该过程的详细分析。该提案旨在对小湖的10 m全新世沉积物核心进行高分辨率多核研究，以与动态植被模型的模拟进行比较。该地区不同地区森林扩张的时机提供了更多信息，以了解这种植被转移的驱动因素和触发因素，该项目旨在改善已经调查的地点的变化的约会，并提供其他当地调查。草原和森林物种在花粉产生和分散方面有所不同，为了减少这种偏见并有助于解释，研究将解决花粉植物关系。这将允许对草原程度及其森林替代的程度进行量化估计。合并的信息将用于检验三个竞争假设：a）随着南美季风的加强，全新世降水逐渐增加，而森林膨胀受到频繁火灾的限制，只有一旦通过阈值就发生； b）降水状态的逐步变化触发了森林快速的扩张；由于种子具有很高的营养价值，人类协助了芳香岛森林的扩散。机械植被模型将通过强迫不同的气候场景并将模拟与定量植被重建进行比较，将其用于假设测试。将设计进一步的数据模型实验，以测试有关草原和森林之间替代稳定状态的当前理论。