Energy requirement for foliage formation is not constant along canopy light gradients in temperate deciduous trees

canopy carbon carbone carbono chemical composition composition chimique corylus avellana couvert crecimiento croissance cubierta de copas drought stress energia energie energy energy requirements fagus sylvatica feuille fraxinus excelsior glucosa glucose growth hojas leaves light ligninas lignine lignins luz ombre populus tremula shade sombra tilia cordata water stress