The chapter presents the dual specificity of tree development and growth, marked by axis mortality and secondary growth. Terminal meristem death leads to the loss of leafy axes, and presents sampling challenges due to the disappearance of tree parts over time. Secondary growth, characterized by ring formation, is primarily associated with woody plants and represents the increase in stem diameter. In contrast to herbaceous plants, tree internodes exhibit ongoing radial growth as long as their axis remains alive, with annual rings indicating the tree's age. The chapter introduces the secondary growth module of the GreenLab approach, which refines traditional forest models by incorporating plant architecture and biomass. The GreenLab model simulates ring formation based on biomass distribution from leaves using fast algorithms, bypassing the need to simulate the propagation process. These advancements have been integrated into various software applications, including GreenScilab, Digiplante, QingYuan, and Gloups, aiming to improve the accuracy and efficiency of forest growth modeling.