This project asks whether the intercept and slope of vessel scaling in twigs changes with age class in Acer, Prunus, Quercus, and Pinaceae. Vessel diameters will be measured at intervals across the 10-12 cm from the apex of twigs in four age classes. To address the physiological question of whether the vessel scaling relationships seen broadly across terrestrial vascular plants are caused by height or cambial age, twigs of seedlings of different ages but similar heights will be compared. To address the ecological question of whether vessel scaling changes with ontogenetic stage to differently adapt to the changing environmental conditions of a tree as it moves from the understory to the subcanopy to the canopy and increases its water access with a larger root system, seedlings will be compared with juveniles and adults.