In trees, bud development is driven by endogenous and exogenous factors such as species and climate, respectively. Alla et al. study bud enlargement and secondary growth at seasonal (3 years) and inter-annual (15 years) scales in two oak species, Quercus ilex (evergreen) and Q. faginea (deciduous), coexisting in north-east Spain. They find that the maximum enlargement rate of buds is reached in summer and responds positively to minimum air temperatures, the latter being a parameter that has been increasing in recent decades. The findings thus have implications for understanding how climate warming may affect bud size and consequently alter crown architecture differentially in sympatric tree species.