What determines the success of restoring the threatened African savanna mahogany (Khaya senegalensis) beyond seed-tree size? A multi-model test of site and maternal-origin effects

Khaya senegalensis (Desr.) A. Juss., the West African savanna mahogany, is Vulnerable on the IUCN Red List due to overexploitation and failing natural regeneration. Restoration programmes commonly assume that selecting seed trees by size improves offspring quality, yet this assumption has rarely been tested against the competing hypothesis that planting site, not seed-tree size, determines regeneration success. This study tests the relative contribution of seed-tree dendrometric characteristics (diameter, height) and planting site to germination and juvenile growth (6-24 months) of K. senegalensis , across two contrasting bioclimatic sites in Côte d'Ivoire (Korhogo: Sudanian savanna; Daloa: humid forest) and six seed-tree size categories, using six complementary statistical approaches (continuous regression, linear mixed models, mediation analysis, non-linear growth modelling, phenotypic plasticity indices, and multi-predictor allometry). Converging across all six approaches, the results show that planting site exerts a decisive influence on germination (71.1% at Korhogo versus 63.9% at Daloa; χ² = 6.09; p = 0.014) and on the entire growth trajectory ( p < 0.001), whereas no seed-tree characteristic affects offspring performance in continuous regression ( p >0.37), mixed models with interaction ( p >0.29), or through a seed-mass mediation pathway (Sobel test, p = 0.46). An exponential growth model outperforms linear or power-law alternatives ( ΔAIC = 13.6-14.7), and multi-predictor allometric equations (diameter and height) explain 97.4% of the variance in total biomass, versus 94.8% for diameter alone; a practical, non-destructive tool for nursery and restoration monitoring. These convergent results indicate that, contrary to the widespread practice of selecting seed trees on size criteria, it is the choice of planting site that truly determines the success of restoring this vulnerable species under the two contrasting bioclimatic conditions tested here. A conclusion calling for a reorientation of priorities in reforestation and agroforestry programmes involving K. senegalensis , pending confirmation across a wider range of sites.