Inter-tree variability of autumn leaf phenology of European beech (Fagus sylvatica) on a site in Ljubljana, Slovenia

Temporal variability of leaf senescence (autumn phenology) was observed in 2020 in 11 European beech (Fagus sylvatica) trees in Tivoli, Rožnik and Šišenski hrib Landscape Park in Ljubljana, Slovenia, and also observed for spring phenology in the same year. General leaf colouring, BBCH94, occurred between 19 and 24 October 2020, with lower inter-individual variability than that of leaf unfolding, BBCH11. The trees had active leaves (time between leaf unfolding and leaf colouring) between 177 and 199 days. In only three trees total leaf fall, BBCH97, occurred before 19 November 2020. Leaf colouring of the tree included in the long-term monitoring program of the Slovenian Environment Agency ARSO occurred on 24 October 2020. This is 7 days later than the 65-year average of the same tree/location and is ascribed to weather conditions. Investigation of tree tissues showed that the width of the last formed tree-ring in the wood varied between 0.39 and 9.61 mm and in the phloem between 0.09 and 0.26 mm, and that the tissues reflect the health condition of the trees.