Impact of recurrent extreme drought events and shrub invasion on Mediterranean cork-oak ecosystem functioning and resilience

干旱等经常性极端气候事件预计将在全球许多地区增加，并可能强烈影响生态系统功能。与此同时，植物入侵也在增加，成为生物多样性的第二大威胁。然而，关于这两个因素如何相互作用并影响生态系统功能和恢复力的知识缺乏。我们将使用具有高社会经济和保护价值的地中海软木橡树生态系统作为模型系统，该系统目前由于干旱和缺乏管理而受到山楂灌木入侵的威胁。与此同时，预计欧洲西南部的极端干旱将增加，但在持续时间和严重程度方面具有很强的空间异质性。入侵的耗水灌木对水的竞争加剧，可能会放大对栓皮栎的干旱影响，最终导致关键树种的临界耐旱阈值被超越，这证实了在入侵生态系统中观察到的更高的树木死亡率。然而，缺乏实验证据。迫切需要更好地理解和预测气候变化下生态系统功能的阈值，这需要：1)对物种和生态系统功能的临界阈值进行实验评估；Ii)高分辨率的气候信息，为未来几十年的极端干旱提供现实的预测；iii)基于生态生理适应、物种相互作用和生态系统恢复力知识的建模工具，以量化入侵生态系统功能的变化。本提案的总体目标是全面了解极端干旱事件和灌木入侵对模型生态系统功能和恢复力的耦合机制，并预测气候变化中的脆弱性区域。我们建议采用跨学科的方法，包括：a)植物生态生理学和实验生态系统研究，实施多因素雨水排除和灌木清除实验，以确定生态系统功能的临界阈值；B)多模式气候预估的区域化，以提供具有代表性和高度空间分辨的干旱情景；C)陆地表面方案的机械生态系统建模，包括土壤-植被、植物-植物和气候-植被相互作用等关键过程的现实表现。将这些方法结合起来，并将生态系统模型与未来情景相结合，将使作为模型系统的栓皮栎林地的可持续性风险评估更加现实。这将与生物多样性、生态系统服务和软木橡树林地保护状况的空间信息联系起来。此外，它将允许更好地评估全球变化的两个主要驱动因素——植物入侵和干旱——之间的相互作用，这与许多半干旱系统高度相关。

Recurrent extreme climate events such as droughts are projected to increase in many regions worldwide and can strongly affect ecosystem functioning. Concurrently, plant invasion is augmenting, causing the second largest threat to biodiversity. However, there is a lack of knowledge on how these two factors interact and impact ecosystem functioning and resilience. We will use a Mediterranean cork-oak ecosystems of high socio-economic and conservation value as a model system which is currently endangered by the invasion of Cistus ladanifer shrubs due to drought and lack of management. Simultaneously, extreme droughts are predicted to increase over Southwest-Europe, but with strong spatial heterogeneity in terms of duration and severity. Enhanced competition for water with invasive water-spending shrubs may amplify drought effects on cork-oaks and ultimately cause critical drought tolerance thresholds of the key-stone tree species to be surpassed, corroborating observed higher tree mortality in the invaded ecosystems. However, experimental evidence is lacking. There is an urgent need to better understand and predict thresholds of ecosystem functioning in a changing climate, which require: i) experimental assessment of critical thresholds for species and ecosystem functioning; ii) highly resolved climate information to provide realistic projections of extreme droughts in future decades, and iii) a modelling tool that feeds on the knowledge of ecophysiological adaptation, species interaction, and ecosystem resilience, to quantify changes in the functioning of the invaded ecosystems. The overall aim of this proposal is to gain comprehensive understanding of the mechanisms of coupled extreme drought events and shrub invasion on the functioning and resilience of the model ecosystem and to project areas of vulnerability in a changing climate. We suggest an interdisciplinary approach consisting of a) plant ecophysiology and experimental ecosystem research implementing a multifactorial rain exclusion and shrub removal experiment to identify critical thresholds of ecosystem functioning; b) regionalisation of multi-model climate projections for the provision of representative and highly spatially resolved drought scenarios; c) mechanistic ecosystem modelling of a land surface scheme with realistic representations of the key processes including soil-vegetation, plant-plant and climate-vegetation interactions. Combing these approaches and applying the ecosystem model with future scenarios will enable a more realistic risk assessment of the sustainability of cork-oak woodland as a model system. This will be linked to spatial information on biodiversity, ecosystem services and conservation status of cork-oak woodlands. Moreover, it will permit a better assessment of the interactions between the two main drivers of global change - plant invasion and drought - which are highly relevant for many semi-arid systems.