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E3 - Extreme Event Ecology

Final Report Summary - E3 (E3 - Extreme Event Ecology)

With global warming, extreme events are very likely to change in intensity and/or frequency and location. The successfully answered leading question of E3 (Extreme Event Ecology) was how (physical) extreme events translate into (biological) extreme impacts. The assessed biological systems ranged from global agricultural yield and price data to European forest productivity, tree-ring, phenological and pollen (proxy-)data to different plant species and provenances in manipulative experiments. The studied extremes mostly relate to air temperature, precipitation, drought summarized by different indices, as well as late spring frosts, but also forest fires, wind throw and air pollution were partly considered.
E3 applied some novel statistical methods, such as quantile regression, to comprehensively analyze changes over the whole distribution of a climate parameter. Impacts of multi-factorial extreme events were consistently described in additive linear models by - for the first time - explicitly modelling nonlinear interaction effects of different variables as well as intensification effects of multiple occurrences of extreme events. Forest succession after wind-throw as well as recovery from a later spring frost event could be monitored spatially explicit, species- and individual-specific with digital repeat photography.
Analyses of extreme event impacts in long-term vegetation data, such as drought responses of tree growth in Europe, revealed an enormous variation of responses which were species- and site-specific, varied with elevation, climate and bioclimatic zone, inter-annual climate fluctuations, drivers on tree-level (traits) as well as provenances leading to localized refinements of vulnerability. For example, in the Mediterranean region the importance of carry-over effects by previous summer drought has increased. The inherent variation in phenological responses to extreme events seems to be a sort of reinsurance against e.g. full losses by late spring frost or danger of ecological mismatch. A declining global warming effect on spring phenology is most likely related to nonlinear responses in extreme warm years / winters.
Several large forward looking manipulative experiments allowed studying fitness, growth and survival/mortality of Scots pine seedlings of 12 provenances under nearly simultaneous occurrence of seasonal heat and drought as well as after consecutive extreme events. Provenance responses to treatments differed considerably and were partly associated with origin, with smaller-sized Mediterranean provenances being better adapted to drought. Seedlings were able to acclimate due to previous drought episodes, reducing the risk of mortality and partly compensating growth reduction. Provenance-specific drought resistance and acclimation potential might facilitate seedling establishment, the persistence of Scots pine forests and offer promising tracks of adaptation to future drought risks. Infrared thermography was used to investigate the stomatal response allowing for the first time to pre-screen and phenotype tree seedlings’ drought sensitivity.
Using Tree DEMON, a novel four chamber system for plant gas exchange of isoprenoid, CO2 and water vapor, E3 was able to study drought impacts on three Scots pine provenances, showing different adaptation of isoprenoid emission during drought stress and after recovery. In contrast, BVOC emissions of Sweet chestnut trees during a heavy drought were only slightly reduced. A 13C labelling study on Scots pine improved our understanding of drought responses on different types and sources (de novo and pools) of isoprenoids and revealed a high heterogeneity for single compounds.
Not all extremes, i.e. rare climatological events, translate into extreme impacts due to resilience or adaptive measures: Inherent variability in responses to extreme events was shown to spread risks, during the last decades lagged or carry-over effects seem to prevail, and previous exposure to extreme events significantly alters the susceptibility of individual plants.