Holm oak decline in human-shaped savannahsphysiological and ecological basis

Zusammenfassung

Holm oak decline in Iberian dehesas, characterized by defoliation, is caused by the interaction of multiple stressors such as climate change-related events, invasive pathogens, and changes in dehesa use and management. Understanding the biochemical and physiological mechanisms preceding and following defoliation remains a challenge. This dissertation conducted a regional study across nine dehesa sites, examining physiological, morphological, and ecological responses underlying holm oak decline. Findings highlighted the oak's ability to acclimate through adjustments in photoprotective compounds. Defoliation occurred when stress exceeded certain physiological threshold. This was accompanied by a shift in energy allocation towards soil resource acquisition through fine root phenotypic plasticity. The loss of tree health was related to upregulated biogeochemical steps and the subsequent downregulation of soil nutrients, forming a tree-soil feedback loop. This research deepens our understanding of holm oak decline, including factors defining tree health, underlying mechanisms, and tree-soil interactions, offering insights to predict, prevent, and mitigate this decline in Iberian dehesa.