Are the conditions of the Italian forests worsening due to extreme climatic events? Evidence from the national monitoring networks ICP Forests - CON. ECO.FOR

Tree defoliation and mortality are triggered in Europe by extreme climatic events that are recurring since the beginning of XXI century. Data from the ICP Forests monitoring networks reveal a general worsening of tree conditions in the last ten years, as consequence of the drought and heat waves that affected the Southern (2017) and Central Europe (2018-2019). In Italy a significant increase of defoliation and tree mortality, assessed on the extensive (Level I) monitoring network, was observed after the 2017 dry summer, which impacted mainly the broadleaved forests (beech and oak forests) in the peninsular regions. Coniferous forests of the alpine belt were severely impacted in 2021, probably because of the co-occurrence of multiple causes, involving windstorm and bark beetle attacks. Chestnut forests suffer from pest (insect and pathogen) attacks. The intensive (Level II) monitoring network provides cases of study and allows to carry out specific cause-effect studies concerning the physiological effects on the environmental impacts, as well to observe the ecological processes following the disturbing events. Defoliation caused by drought or pest attacks induces the loss of physiological defenses (namely nonstructural carbohydrates), that need several years to be restored. Then, the occurrence of more frequent and repeated heat and drought waves can produce irreversible effects. In this view, the long-term forest health monitoring is key to detect the extent and direction of changes in forest structure and composition, and represents an important tool for forest conservation and management.