Interactions between fire, vegetation and climate

该项目旨在提高对火、植被和气候之间相互作用的理解。特别是，我将讨论火、植被和气候之间的相互作用何时以及在哪里导致植被的多种稳定状态。多重稳定性对生态系统的弹性有影响，包括突然变化的可能性。基于理论分析、卫星数据、野外研究和模拟模型，预计火灾-植被相互作用将导致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，草支持火灾频繁发生，这阻碍了树木的建立。另一方面，由粗燃料和潮湿的小气候形成的森林可以排除火灾。火和植被之间的这种反馈稳定了树木覆盖率高或低的植被状态。直到最近，火和植被之间的反馈只被区域或概念性模型捕捉到。在JSBACH陆面模式中实施了一个复杂的火灾模式，首次提供了由于火-植被反馈而导致的植被多种稳定状态的全球图像。JSBACH具有作为全球模式的优势，并且可以与MPI-ESM地球系统模式耦合。然而，区域植被模型和离线(与大气无耦合)模型受益于更好的观测评估和详细的过程描述。在这里，我提出了不同复杂性的模型(JSBACH，LPJ-Guess，aDGVM，aDGVM2)之间的比较，以评估模型对气候敏感的稳健性，并解决不同的过程表示如何影响火和植被之间的反馈。地表通过反照率、蒸腾作用和地表粗糙度的变化对气候产生强烈影响。因此，改变陆地表面状态的局部火-植被过程可能会引发气候的大规模转变。为了研究这种尺度的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。除了研究所建模的火-植被-气候相互作用外，我的目标是用数据来检验这些模型。新的高分辨率卫星数据产品能够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火灾发生对植被变化的模型敏感性提供基础。拟议研究的结果将综合起来，以解决火灾、植被和气候之间何时何地相互作用是重要的问题，以及关于火灾、植被和气候之间相互作用的剩余知识差距。

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.