The continuous formation of earlywood vessels is crucial for the growth of ring-porous hardwoods. Kudo et al. study Quercus serrate seedlings and find that a combination of localized heating and disbudding of dormant stems results in earlier cambial reactivation and differentiation of first vessel elements than in non-heated seedlings. A few narrow vessel elements are formed during heating after disbudding, while many large earlywood vessel elements are formed in heated seedlings with buds. The results suggest that elevated temperature is a direct trigger for differentiation of first vessel elements, and that whilst bud growth is not essential for differentiation of first vessel elements, it might be important for the continuous formation of wide vessel elements.