Xylogenesis Responses to a Mediterranean Climate in Holm Oak (Quercus ilex L.)

Quercus ilex L., an evergreen oak species typical of the western and central Mediterranean basin, is facing decline and dieback episodes due to the increase in the severity and frequency of heat waves and drought events. Studying xylogenesis (the wood formation process) is crucial for understanding how trees respond with their secondary growth to environmental conditions and stress events. This study aimed to characterize the wood formation dynamics of Quercus ilex and their relationship with the meteorological conditions in an area experiencing prolonged drought periods. Cambial activity and xylem cell production were monitored during the 2019 and 2020 growing seasons in a Q. ilex forest located at the Vesuvius National Park (southern Italy). The results highlighted the significant roles of temperature and solar radiation in stimulating xylogenesis. Indeed, the correlation tests revealed that temperature and solar radiation positively influenced growth and cell development, while precipitation had an inhibitory effect on secondary wall formation. The earlier cell maturation in 2020 compared to 2019 underscored the impact of global warming trends. Overall, the trees studied demonstrated good health, growth and adaptability to local environmental fluctuations. This research provides novel insights into the intra-annual growth dynamics of this key Mediterranean species and its adaptation strategies to climatic variability, which will be crucial for forest management in the context of climate change.