An integrated study of bud development and phenology enhances our understanding of coexistence and reproduction in two Mediterranean Quercus species

Vegetative growth is a two-phase process involving slow cell division followed by potentially rapid cell expansion. In seasonal climates, trees adjust these developmental sequences to exploit favourable growth periods optimally. However, elucidating the precise mechanistic links between environmental drivers and developmental processes in trees remains challenging. Detailed analyses of apical bud organogenesis, and phenology, are used to study the coexistence of the evergreen Quercus ilex L. subsp. ballota (Desf.) Samp. and the deciduous Q. faginea Lam. at a Mediterranean site where both co-occur. Phenological and organogenetic patterns proved similarly highly synchronised in both species, but bud burst was later in Q. ilex than in Q. faginea . Nevertheless, in both species, organogenesis commenced in early spring (bud swelling or bud burst) and had finished by mid-September, with bud development completed by November. Winter buds contained fully preformed embryonic shoots with well-developed male inflorescences and initiated female inflorescence meristems. The results suggest that organogenesis and shoot extension may compete for resources during summer, potentially explaining the alternating pattern of years of vigorous primary growth observed in Q. ilex but not in Q. faginea . Moreover, the unexpectedly early initiation of female inflorescence meristems in both species – relative to key phases of bud and fruit development – suggests that the advanced stages of fruit development described in mast years may overlap with the initiation of inflorescence meristems and the formation of new buds. This could explain the occurrence of smaller buds and reduced flowering in the year following mast events – a pattern not observed in years of normal fruiting.