Interactions between fire, vegetation and climate

该项目旨在提高人们对火灾、植被和气候之间相互作用的认识。特别是，我将讨论火灾，植被和气候之间的相互作用在何时何地导致植被的多种稳定状态。多重稳定性对生态系统的恢复力有影响，包括突变的可能性。基于理论分析、卫星数据、野外研究和模拟模型，预测了火-植被相互作用下植被的多种稳定状态。由于不同的燃料特性和不同的小气候，草支持频繁的火灾，这阻碍了树木的建立。另一方面，森林的形成与粗糙的燃料和潮湿的小气候可以排除火灾。这种火灾和植被之间的反馈稳定了植被的高或低树木覆盖状态。直到最近，火灾和植被之间的反馈只被区域或概念模型所捕捉。在JSBACH陆地表面模型中实现复杂的火灾模型，首次提供了由于火灾-植被反馈而导致的植被多种稳定状态的全球图像。JSBACH具有全球模式和与MPI-ESM地球系统模式耦合的可能性。然而，区域植被模式和离线模式（不与大气耦合）受益于更好的观测评估和详细的过程表示。在这里，我提出了不同复杂性模型（JSBACH, LPJ-GUESS, aDGVM, aDGVM2）之间的比较，以评估模型对气候敏感性的鲁棒性，并解决不同过程表示如何影响火与植被之间的反馈。地表通过反照率、蒸腾和地表粗糙度的变化对气候有很强的影响。因此，改变地表状态的局部火-植被过程可以引发大规模的气候变化。为了研究这种尺度相互作用并评估对气候的潜在影响，我建议使用MPI地球系统模型。除了研究模拟的火-植被-气候相互作用外，我的目标是用数据测试模型。新的高分辨率卫星数据产品可以评估火灾发生对植被覆盖变化的反应。对这些卫星数据集的分析将为评估模拟的火灾发生对植被变化的敏感性提供基础。拟议研究的结果将被综合，以解决火灾、植被和气候之间的相互作用在何时何地是重要的问题，以及关于火灾、植被和气候之间相互作用的知识的剩余空白是什么。

This project aims to improve the understanding on the interactions between fire, vegetation and climate. In particular, I will address when and where interactions between fire, vegetation and climate cause multiple stable states of vegetation.Multi-stability has implications for an ecosystem's resilience including the possibility for abrupt changes. Multiple stable states of vegetation due to fire-vegetation interactions are expected based on theoretical analyses, satellite data, field studies and simulation models. Due to different fuel characteristics and a different microclimate grasses support frequent fires, which hinders the establishment of trees. On the other hand the formation of a forest with coarse fuels and moister microclimate can exclude fires. This feedback between fire and vegetation stabilizes vegetation states with high or low tree cover. Until recently the feedback between fire and vegetation was only captured by regional or conceptual models. The implementation of a complex fire model in the JSBACH land surface model provided the first global picture of multiple stable states of vegetation due to a fire-vegetation feedback.JSBACH has the advantage of being a global model and the possibility of being coupled to the MPI-ESM Earth system model. However, regional vegetation models and offline (no coupling to atmosphere) models benefit from better evaluation with observations and a detailed process representation. Here I propose a comparison between models with different complexity (JSBACH, LPJ-GUESS, aDGVM, aDGVM2) to assess the robustness of the models sensitivity to climate and address how a different process representation influences the feedback between fire and vegetation. The land surface has a strong influence on climate through changes in albedo, transpiration and surface roughness. Thus, local fire-vegetation processes which alter the land surface state can trigger large scale transitions in climate. To investigate this scale interaction and assess potential effects on climate, I propose to use the MPI Earth System Model.In addition to investigating the modelled fire-vegetation-climate interactions, I aim to test the models with data. New high resolution satellite data products allow assessment of the response of fire occurrence to changes in vegetation cover. An analysis of these satellite datasets will provide a basis to evaluate the modelled sensitivity of fire occurrence to vegetation changes.The results of the proposed studies will be synthesized to address the questions when and where interactions between fire, vegetation and climate are important and what are the remaining gaps of knowledge on interactions between fire, vegetation and climate.