Study on the health of heterotopic beech (Fagus sylvatica L.) forests in central Italy related to the presence of the pathogen Biscogniauxia nummularia

The aim of this study was to explore the health status of adult beech (Fagus sylvatica L.) trees in heterotopic stands along a latitudinal gradient in central Italy (Tuscany and Lazio). The research is part of a multidisciplinary project addressing the complex issue of defining conservation strategies for these forests, which are rich in adaptive biodiversity, but threatened by climate change and the emergence of secondary pathogens. Canopy health was surveyed according to the ICP Forests international protocol, and the presence of Biscogniauxia nummularia, the opportunistic fungal pathogen causing emerging charcoal canker disease on beech, was assessed and quantified by real-time PCR in symptomless tissue. At abyssal beech populations in central Tuscany these data were combined with the measure of photosynthetic efficiency on samples taken, in tree climbing, from the upper tree crown, and the assessment of canopy functionality by unmanned aerial vehicle (UAV) remote sensing. In the beech twigs sampled in the abyssal populations, the presence (frequency and quantity) of B. nummularia DNA was limited, and fluorescence parameters of the host indicated normal photosynthetic activity consistently with vegetation indices. In the other beech populations B. nummularia was more frequent and abundant in the canopies of the southernmost heterotopic stands. The high amount of B. nummularia DNA in marginal populations suggests that it is from these, due to a combination of biotic and abiotic drivers, that the contraction of continuous range of beech may begin in the near future. The issue would deserve further investigation from an evolutionary ecology perspective.