Periodic Reporting for period 1 - COCOS (effects of Climatic extremes On eCOsystem Stability)
Reporting period: 2022-10-10 to 2024-10-09
The intensity and frequency of extreme climatic events, such as floods, heatwaves and extreme droughts, are increasing, along with their impact on society. Extreme climatic events (ECE) are responsible for significant economic losses worldwide. In Europe alone, ECE caused economic losses estimated at EUR 738 billion during 1980-2023. To face the effects of ECE, the European Commission adopted the European Strategy on Adaptation to Climate Change in 2021. The strategy aims to promote a faster, swifter and more systemic action to address the impacts of climate change.
Extreme climatic events can disrupt the temporal stability of ecosystem functions (e.g. plant biomass production), in turn also affecting ecosystems' ability to deliver services that support human well-being (e.g. food production). Biodiversity is thought to enhance ecosystems' response to extreme events. High biodiversity is expected to increase ecosystems' resistance (i.e. their capacity of buffering ECE) and recovery (i.e. their ability to return to pre-disturbance functioning after ECE). Different hypotheses have been proposed to explain how biodiversity supports ecosystems under ECE. However, only a few studies have empirically tested these hypotheses, and most have reported contrasting results. Possible explanations for the lack of consensus include: differences in spatial extent and, consequently, the type of data used to measure ecosystem functions and their stability (e.g. local studies using field-collected data vs. continental studies using remote sensing data); the use of unstandardized measures of intensity of ECE, which has likely hindered comparisons among studies; and a predominant focus on taxonomic diversity to explain biodiversity-mediated mechanisms of ecosystem stability. Concerning the last issue, neglecting the multifaceted nature of biodiversity may have limited our understanding of its role in mediating ecosystems' response to ECE. For example, incorporating functional traits in the picture could provide a more mechanistic understanding of how ecosystems respond to ECE.
In this context, COCOS aimed to address gaps and limitations in previous studies and provide a first assessment of the relationship between biodiversity and ecosystem stability under ECE at a broad spatiotemporal scale (Work Package 2). To this end, within COCOS, I used global, long-term time-series of field-collected vegetation data from the LOTVS dataset to measure ecosystem's resistance and recovery. I then combined these data with temperature and precipitation time-series to compute standardized indices of ECE intensity, thereby enabling comparison with future research. Importantly, I incorporated functional traits into the analyses to explain the biodiversity-stability relationship under ECE in light of species' ecological strategies. In addition to testing the association between biodiversity and ecosystem stability, COCOS aimed to investigate whether and how ECE can favor critical transitions, i.e. whether they can push ecosystems away from their reference state (and potentially toward a new reference state) (Work Package 3).
Extreme climatic events can disrupt the temporal stability of ecosystem functions (e.g. plant biomass production), in turn also affecting ecosystems' ability to deliver services that support human well-being (e.g. food production). Biodiversity is thought to enhance ecosystems' response to extreme events. High biodiversity is expected to increase ecosystems' resistance (i.e. their capacity of buffering ECE) and recovery (i.e. their ability to return to pre-disturbance functioning after ECE). Different hypotheses have been proposed to explain how biodiversity supports ecosystems under ECE. However, only a few studies have empirically tested these hypotheses, and most have reported contrasting results. Possible explanations for the lack of consensus include: differences in spatial extent and, consequently, the type of data used to measure ecosystem functions and their stability (e.g. local studies using field-collected data vs. continental studies using remote sensing data); the use of unstandardized measures of intensity of ECE, which has likely hindered comparisons among studies; and a predominant focus on taxonomic diversity to explain biodiversity-mediated mechanisms of ecosystem stability. Concerning the last issue, neglecting the multifaceted nature of biodiversity may have limited our understanding of its role in mediating ecosystems' response to ECE. For example, incorporating functional traits in the picture could provide a more mechanistic understanding of how ecosystems respond to ECE.
In this context, COCOS aimed to address gaps and limitations in previous studies and provide a first assessment of the relationship between biodiversity and ecosystem stability under ECE at a broad spatiotemporal scale (Work Package 2). To this end, within COCOS, I used global, long-term time-series of field-collected vegetation data from the LOTVS dataset to measure ecosystem's resistance and recovery. I then combined these data with temperature and precipitation time-series to compute standardized indices of ECE intensity, thereby enabling comparison with future research. Importantly, I incorporated functional traits into the analyses to explain the biodiversity-stability relationship under ECE in light of species' ecological strategies. In addition to testing the association between biodiversity and ecosystem stability, COCOS aimed to investigate whether and how ECE can favor critical transitions, i.e. whether they can push ecosystems away from their reference state (and potentially toward a new reference state) (Work Package 3).
At the start of the project, I gathered and processed different types of data (Work Package 1) for use in Work Packages 2 and 3. Using LOTVS vegetation time-series, I computed indices of resistance and recovery of ecosystem functions based on plant biomass and cover, as well as biodiversity metrics at the community level, such as species richness. Additionally, I processed data on the anthropogenic treatments to which vegetation communities had been subjected (e.g. fertilization or grazing). I then used functional traits data to compute indices of functional diversity and to summarize the dominant ecological strategy of vegetation communities (i.e. conservative vs. acquisitive strategy). Finally, using approximatively 70-year long temperature and precipitation time-series, I computed indices of compound dry-hot extreme events, i.e. extreme drought and heat occurring simultaneously. After completing this initial phase of data preparation, I used statistical models to analyze how biodiversity related to ecosystem resistance and recovery under varying intensities of compound dry-hot extremes. I also explored how this relationship differed across communities subjected to different land-use treatments. I presented the results of these analyses at three international scientific conferences (2 oral presentations and 1 poster), as well as at events attended by a wide audience, such as the 2024 EuroScience Open Forum in Katowice in Poland. While processing data for Work Package 1, I also completed and published a first manuscript related to COCOS. This manuscript focused on a smaller spatial extent than planned for COCOS, as the study area consisted in three grassland regions in Germany. Moreover, it used a different dataset than the one prepared in Work Package 1. Nonetheless, the study’s objective, data, and analytical approach fully aligned with those planned for Work Packages 1 and 2. Indeed, I tested the role of both taxonomic and functional diversity in mediating the response of plant biomass to extreme drought in Central European grasslands.
The key findings from COCOS highlight that biodiversity is associated with the resistance and recovery of vegetation-related ecosystem functions, such as plant biomass and cover, under extreme climatic events. Among the different facets of biodiversity, taxonomic diversity, measured as the number of plant species in a community, showed the stronger association with resistance. Specifically, species-rich communities were better able to withstand extreme events. In contrast, taxonomic diversity did not seem to enhance recovery after extreme events, particularly in communities subjected to fertilization. Concerning functional traits, the results showed that more functionally diverse communities were generally more resistant. Whereas, communities dominated by species with an acquisitive strategy, typically less functionally diverse, tended to recover better after ECE. Notably, the relationship between functional traits and ecosystem stability came out clearly when analyses focused on a regional spatial extent. At a broader spatial extent, however, results were less clear and did not align with what predicted by the theory. Overall, the findings from COCOS emphasize the importance of maintaining sufficient biodiversity to help buffer ecosystem functions against the impacts of ECE.