Seed phenotypic variation and traits repeatability in Afzelia africana along a climatic gradient provide insights for seed sourcing in forest restoration

Seeds are key components of plant life histories, ensuring reproduction, dispersal, and adaptation to changing environments. Understanding intraspecific variation in seed phenotypic traits is critical for the management of genetic resources, conservation, and forest restoration. The African oak tree, Afzelia africana Sm. Ex Pers. is a multipurpose tree species widely distributed across sub-Saharan Africa. However, its populations are threatened by poor natural regeneration, illegal logging, and chronic pruning. This study assessed within- and among-tree variation and trait repeatability based on measurements of 9,330 seeds collected from 63 A. africana trees across five provenances and three climatic zones. Seeds were measured for seed length, width, thickness, and weight. Data were analyzed using linear mixed models, variance component analysis, and univariate and multivariate phenotypic plasticity indices. Repeatability, coefficients of variation, and hypervolume analyses were further performed to assess within-tree variability and multidimensional phenotypic diversity. Significant variation among climatic zones and provenances was observed for all seed traits except seed width. The largest, heaviest, and thickest seeds were recorded in the wettest zone, whereas the lowest values occurred in the driest zone. Most of the phenotypic variation occurred within trees (31–56%), whereas variation among trees accounted for 19–22% and variation among climatic zones was less than 25%. Phenotypic plasticity was generally low, especially for seed width and thickness (< 0.12). Although statistically significant, repeatability estimates were moderate, particularly for seed length and weight (0.33–0.37), suggesting potential for selection in forest restoration programs. Coefficients of variation and hypervolume analyses further revealed significant heterogeneity in seed traits within mother trees, with no significant effect of climatic zones, indicating that microclimatic and maternal factors may play a stronger role than broad climatic gradients in shaping seed morphological diversity. Nine mother trees were identified as promising candidates for seed collection for forest restoration programs.