Assessing the impacts of coppice-with-standards in thermophilous deciduous oak forests by monitoring microclimate, plant community diversity and tree health

Global warming impairs forest functionality through thermophilization processes. Based on recent evidence, forest microclimatic effects are especially pronounced in regions with warm macroclimates, such as the Mediterranean. However, forests can mitigate thermophilization processes by buffering the microclimate, depending on forest structure and density, which in turn are often determined by the silvicultural management. Coppice-with-standard is one of the oldest and most widespread silvicultural practices in Italy. Thanks to the provision of firewood, this is in line with the EU Forest Strategy that supports the use of renewable energy to counteract climate change. On the other hand, coppicing has a strong impact on the forest structure with possible alteration of microclimate which, in combination with frequent heat and drought events, can lead to two possible effects, the first related with the understorey: changes in community diversity with impoverishment of herb species associated to the forest (forest specialists) with alteration of their functionality, the second with the tree component: impairment of the performance of trees left from the cut as standards, caused by their sudden exposure to sunlight and possible heat waves. Considering the lack of data on these issues in Mediterranean areas, in 2020, we established an air and soil temperature and vegetation monitoring network in high forests and coppice-with-standards sites in three mixed deciduous forests in Tuscany dominated by Quercus cerris and Q. petraea. Moreover, in the first two forests (Bosco ai Frati - Northern Tuscany and Aratrice - Southern Tuscany) we analyzed the long-term responses of the understorey to coppicing in terms of taxonomic, functional and phylogenetic diversity and alteration of functional traits of forest specialist and generalist herb species. In the third forest (Berignone-Tatti, Central Tuscany), that will be coppiced in winter 2024, we are currently monitoring understorey vegetation together with the tree component in order to assess the early response of the understorey in terms of the above variables and tree standards in terms of crown transparency, chlorophyll content and fluorescence. First available evidence on the long-term responses show that coppicing significantly reduces the forest's temperature buffering capacity, and increases understorey species richness by favouring generalist taxa, but significantly decreases the proportion of forest specialists. The understorey community in coppiced forests appears to be made of more warm-adapted species. Moreover, coppicing also alters phylogenetic evenness, diversity and community-weighted mean leaf dry matter content, pointing to ongoing acclimation processes to warmer microclimates.