preprint · bioRxiv (Cold Spring Harbor Laboratory)
Restoration strategies for the vulnerable West African savanna mahogany, Khaya senegalensis, often assume that collecting seeds from larger trees yields higher-quality offspring. A multi-model investigation across contrasting bioclimatic sites in Cote d'Ivoire evaluated whether seed-tree dimensions or the planting location determine germination and early growth over six to twenty-four months. The findings reveal that planting site strongly dictates seedling success, yielding higher germination and superior growth trajectories in savanna conditions compared to humid forest environments. In contrast, seed-tree height and diameter show no meaningful effect on offspring performance or seed mass. Additionally, multi-predictor allometric models using both diameter and height accurately predict juvenile biomass. Consequently, effective conservation and agroforestry efforts for this overexploited species depend primarily on selecting suitable planting environments rather than prioritising the physical size of seed-bearing trees.
The African savanna mahogany faces severe pressure from overexploitation, habitat loss, and climate change. By showing that site conditions matter far more than parent tree size, these findings challenge conventional forestry assumptions. Reforestation programmes can significantly improve restoration success and resource efficiency by targeting ecologically optimal planting locations rather than expending effort searching for exceptionally large mother trees.
This research provides applied guidance for operators of forestry nurseries, agroforestry initiatives, and environmental restoration programmes in West Africa. By replacing seed-tree size criteria with strict site-selection protocols, practitioners can improve seedling survival rates and optimise nursery sourcing. The allometric equations also offer practical tools for monitoring biomass accumulation. The insights represent applied and field-tested operational knowledge ready for integration into ongoing land-management and tree-planting frameworks.
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Abstract Khaya senegalensis (Desr.) A. Juss., the West African savanna mahogany, is listed as Vulnerable on the IUCN Red List due to prolonged commercial and medicinal overexploitation, compounded by failing natural regeneration amid growing deforestation and climate change. Restoration strategies generally rest on the implicit assumption that rigorous selection of seed trees based on their size improves offspring quality. Yet this assumption has never been confronted with the competing hypothesis of a determinism dominated by the planting site, using statistical approaches of adequate power. 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 , using six complementary analytical approaches: continuous regression, linear mixed models with site × seed-tree interaction, seed-mass mediation analysis, non-linear growth-trajectory modelling, between-site phenotypic plasticity indices, and multi-predictor allometric equations, across two contrasting bioclimatic sites in Côte d’Ivoire (Korhogo: Sudanian savanna, and Daloa: humid forest) and six seed-tree categories. Converging across all these approaches, the results show that the planting site exerts a decisive influence on germination (71.1% at Korhogo versus 63.9% at Daloa; χ ² = 6.09; p = 0.014) and on the entire growth trajectory ( p < 0.001), whereas no seed-tree characteristic affects offspring performance, whether 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 fits better than linear or power-law models (Δ AIC = 13.6-14.7 depending on site), and multi-predictor allometric equations (diameter and height) explain 97.4% of the variance in total biomass, versus 94.8% for the single-predictor model. 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. A conclusion calling for a reorientation of priorities in reforestation and agroforestry programmes across West Africa.
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DOI: 10.64898/2026.08.12.744298
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