Elements of a functional-structural plant model

Abstract Functional–structural plant (FSP) models explicitly couple aspects of plant function with three-dimensional plant structure, enabling the analysis of resource capture, growth, or competition (among others) that cannot be addressed with horizontally homogeneous vegetation models or tissue-level mechanistic models. In this paper we provide a platform-agnostic guide to designing and building FSP models, organized around four core elements: plant function, geometry, topology, and environment. We discuss how these elements can be represented at different biological and spatial scales, emphasizing the need to balance model realism with data requirements and computational cost, always using the goal of the research project as guidance. We outline common approaches for modelling carbon and nutrient acquisition and allocation, alternative structural representations (from detailed organ meshes to voxels and crown-envelope), and formalisms to represent dynamic development (L-systems and graph grammars). We discuss different time-integration methods for dynamic FSP models and argue how a single “model timestep” is rarely meaningful. Finally, we review strategies for parameter estimation and highlight emerging applications—such as digital twins and the interplay between FSP modelling and artificial intelligence. Together, all these considerations provide a basis for developing FSP models that are both scientifically informative and practically feasible.