Dr Manuel Encinas graduated with a thesis entitled “Holm oak decline in human-shaped savannahs: Physiological and ecological basis” today at the Faculty of Science and Technology (UPV/EHU). Dr Encinas has participated in the H2020 project Holisoil, as well as the IBERYCA project funded by AEI. He also has been granted with the FPI (PRE2018-083275) Scholarship by AIE to carry out his research. Dr Encinas’s thesis has been supervised by Professor Jorge Curiel Juste (BC3) and Raquel Esteban Terradillos (UPV/EHU).

Abstract: 

Holm oak decline in Iberian dehesas, characterized by the loss of tree vigour and 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 may allow us to identify and predict potential hotspots of tree decline and mortality and implement future action that counteracts this phenomenon. This dissertation conducted a regional study across nine dehesa sites, examining physiological, morphological, and ecological responses underlying holm oak decline. Findings highlighted the tree’s ability to acclimate through adjustments of photoprotective compounds. However, defoliation occurred when stress exceeded a certain physiological threshold and photoprotection mechanisms no longer prevented photooxidative damage. At this point, declining holm oaks triggered a second mechanism to mitigate the stress. An increase in fine root phenotypic plasticity was observed at expense of available carbohydrates and the maintenance of foliage. This presumably increased soil resources uptake. Additionally, the loss of tree health was related to upregulated of certain biogeochemical steps and the subsequent downregulation of key soil nutrients for tree health. Hence a tree-soil feedback loop that boosted tree decline was stablished. Overall, this research deepens our understanding of holm oak decline, by characterizing holm oak health, describing mechanism underlying the loss of tree vigour and exploring its relationship with soil chemistry and microbial communities offering insights to predict, prevent, and mitigate this decline in Iberian dehesa.

Thesis Committee: 

Jose Ignacio García Plazaola

Lur Epelde Sierra

Cecillia Brunetti

Ana Rincón Herraz

Guillermo Gea Izquierdo