The rapid growth of urban areas underscores the need for developing semantically rich 3D city models representing a variety of urban objects and integrating the results from the analysis and simulation of urban processes and environment. Adhering to standards such as CityGML, these 3D city models offer immense value in urban planning, development, and management. By encoding the spatial, functional, and thematic information in a standardized way, they provide a comprehensive digital representation of cities. This enables city authorities to evaluate the impact of proposed developments and thereby make informed decisions. CityGML-based city models facilitate the progression towards smarter, more efficient, and more sustainable cities by supporting interoperability across different systems and platforms. This fosters collaboration and data exchange among diverse stakeholders.</p> <p>This paper contributes to the development of semantically rich and interoperable 3D city models by proposing a conceptual model for Application Domain Extension (ADE) of the CityGML 3.0 Vegetation module. The ADE enhances the <em>SolitaryVegetationObject</em> and <em>PlantCover</em> feature types with additional properties by leveraging the new “hook” mechanism available in CityGML 3.0. Furthermore, it considers the dynamics of vegetation in terms of growth and management through modelling of dynamic data based on the <em>Dynamizer</em> module. Additionally, new data types, code lists and enumerations appropriate to the ADE domain are defined, providing a unified description of the vegetation’s specific characteristics that are comprehensive across different platforms and disciplines. The Vegetation ADE’ conceptual model opens several avenues for future research, including development of more accurate vegetation simulations and analyses, investigation of urban heat island effect or environmental impact assessments.