Monitoring European beech leaf phenology along its southern extreme of range distribution in different years in relation to site characteristics and silvicultural treatments

<p>The leaf phenology is closely related to environmental factors, that makes this trait a robust indicator of the impacts of climate on forest ecosystems, and trees adaptive capacity to external stressors. For that, the leaf phenology monitoring can be considered a useful tool to understand how trees respond to disturbances, whether environmental or human. <em>Fagus sylvatica </em>L<em>. </em>is a species with a wide natural range in Europe, but few studies about leaf phenology were conducted, especially as monitoring effects post silvicultural treatments.</p><p>The aim of this work was to apply the leaf phenology to monitor the effects of the main climatic parameters and different silvicultural treatments to evaluate how to apply a sustainable forest management and to increase forest resilience and production.</p><p>The study was conducted in three different sites of the Life AForClimate Project, in Toscana (Giogo-Casaglia complex - FI), Molise (Roccamandolfi forest - IS) and Sicilia (Monte Soro – ME). Each site has been divided into 4 sectors based on the aspect (north/south) and the altitude range (high/low, 1st and 4th quartile of local altitudinal range respectively), to cover the extremes of local beech distribution range. Each sector has been divided into 15 plots, which were subjected to different silvicultural treatments: low intensity thinning (D1), high intensity thinning (D2), and Control (C), where the leaf phenology was observed.</p><p>This study concerns the results of the pre-intervention and post intervention phenological monitoring. Leaf flushing and leaf senescence were monitored weekly from end of March to June, and from September to November, respectively.  Phenological monitoring was performed on 60 healthy, dominant, or co-dominant beech trees with a diameter at breast height of at least 25 cm in each site.</p><p>The phenophases of leaf flushing and leaf senescence were recorded <em>in situ</em> using a modified scale of BBCH. All data were computed in Day Of the Year (DOY). The score 3 (leaf unfolding), when young leaves starting to emerge from the upper part of the bud was considered the bud break and the start of the growing season, while the score 7 (leaf colouring), when the leaf colour yellowing, was computed as the end of the growing season The length of the growing season was computed as the difference between scores 7 and 3.</p><p>The <em>in situ </em>monitoring was used to calibrate a remote sensing approach to estimate leaf phenophases from Copernicus Sentinel 1 radar satellite. This method was used to estimate phenophases in all plats for the entire period of observation before and after the silvicultural treatments.</p><p>The phenological data was compared in relation to altitude, aspect, main climatic factors (air temperature and precipitation in the four sectors) and silvicultural treatments.</p><p>Significant differences were resulted from the effect of different factors particularly comparing the growth season length.</p>