Abstract
<title>Abstract</title> <p> Architectural analysis provides a powerful analytical framework for understanding the ontogenetic trajectories of tree species and their adaptive responses to environmental constraints. Despite their ecological, economic, and cultural importance in West African agroforestry systems, the architectural development of <italic>Khaya senegalensis</italic> (Desr.) A. Juss. (Meliaceae) and <italic>Pterocarpus erinaceus</italic> Poir. (Fabaceae), two overexploited taxa classified as Vulnerable on the IUCN Red List, had never been formally described. This study presents the first complete characterization of their architectural development, from the seedling stage to senescence, based on architectural and retrospective analyses conducted on 360 individuals per species across seven localities along a south-north bioclimatic gradient in Côte d'Ivoire, covering contrasting vegetation zones ranging from dense humid forest to dry Sudanian savanna. Both species display well-defined ontogenetic trajectories comprising four phases: juvenile establishment, architectural construction, reproductive transition, and crown restructuring associated with ageing. Distinct architectural models were identified: <italic>K. senegalensis</italic> conforms to Rauh's model, characterized by a monopodial orthotropic trunk with indefinite growth and rhythmic acrotonic branching; <italic>P. erinaceus</italic> follows Troll's model, in which the orthotropic trunk progressively gives rise to a sympodial plagiotropic system with mixed terminal and lateral flowering. Architectural units, defined as the minimal structural organization enabling a species to reach reproductive maturity, were established at the adult stage: that of <italic>K. senegalensis</italic> comprises four axis categories and five branching orders, while that of <italic>P. erinaceus</italic> comprises three axis categories and up to six branching orders in old trees. Significant variation in growth-unit morphology among habitats and localities ( <italic>P<0.05</italic> ) revealed the architectural plasticity of both species in response to ecological gradients. The calculated Favourable Development indices ( <italic>FDi</italic> ) identified Bouaké and Katiola as optimal zones for <italic>K. senegalensis</italic> , and Bouaké and Toumodi for <italic>P. erinaceus</italic> , providing objective spatial criteria for reforestation planning. These findings demonstrate that architectural traits are robust indicators of development, adaptive strategies, and crown functioning. By linking structural organization to productivity, resilience, and regeneration potential, this study provides a scientific basis for integrating architectural analysis into reforestation programmes, sustainable forest management, and the design of agroforestry systems for threatened African tree species facing growing climatic and anthropogenic pressures. Complementary regression analyses further showed that phytomer number, rather than internode elongation, primarily governs growth-unit length in both species, and that growth unit diameter scales positively with growth unit length; a multivariate analysis of variance (MANOVA) confirmed that ontogenetic stage and locality, but not habitat alone, robustly structure growth-unit morphology. </p>