African Mahogany Rewrites Its Own Life Story Across Three Contrasting Savannas

In the savannas of Côte d’Ivoire, one of West Africa’s most iconic trees is quietly telling scientists that there is no single blueprint for what a mature tree should look like. Savanna mahogany, known scientifically as Khaya senegalensis, has long been prized for its termite-resistant timber and its role in traditional medicine, where bark extracts are used against malaria and fevers. Yet the species is under such intense pressure from logging and charcoal production that it now appears on Appendix II of CITES, the international treaty regulating trade in endangered species. A new study, published in Discover Plants, has taken an unusually detailed look at how these trees change shape as they grow, and the findings challenge a long-standing assumption about how trees adapt to their environments.

A team of researchers led by Bi Irie Ghislain Tré of Nangui Abrogoua University, working with colleagues in Côte d’Ivoire and France, measured 550 mahogany trees across three natural stands spanning the country’s major agro-ecological zones. The sites could hardly be more different in character. Pouniakele, in the northern Sudanian savanna, receives about 1,200 millimetres of rain a year and is the driest and most disturbed of the three, with pastures and agricultural exploitation pressing in on the trees. Kouassi-N’Dawa, in the east, is a sacred forest on a hill where human activity is deliberately limited by cultural tradition. Koumokro, in the centre-east, is a community forest sitting in the climatic transition zone between subtropical and humid tropical conditions, receiving roughly 1,300 millimetres of annual rainfall. Measurements were collected between January 2022 and June 2024, all on standing trees in their natural habitat, using non-destructive techniques.

The methodological design is what gives the study its power. Rather than treating all trees as a single population, the researchers sorted them into three diameter-based cohorts that serve as proxies for developmental stages: young trees between 5 and 25 centimetres in diameter, non-exploitable adults from 25 to 40 centimetres, and exploitable adults of 40 centimetres or more, the size class targeted by selective cutting for charcoal. On every tree, eleven traits were recorded, ranging from the classic dendrometric measures of trunk diameter, total height, bole height and crown spread to a suite of foliar characters including leaf length and width, petiole length, the number of leaflets per leaf, and the length and width of individual leaflets. This dual focus on architecture and foliage allowed the team to track how different parts of the tree’s form respond to different pressures across the lifespan.

The statistical treatment was equally rigorous. After standardisation, the data were subjected to analysis of variance to detect differences among sites within each cohort, then to hierarchical cluster analysis to group trees with similar morphology, and finally to discriminant function analysis to identify which traits did the best job of separating those groups. Bartlett’s test of sphericity and the Kaiser-Meyer-Olkin measure confirmed the datasets were suitable for multivariate work. The results were strikingly consistent: at every developmental stage, and again when all 550 trees were pooled, the analyses resolved three distinct morphological groups, and leaf length and leaflet length emerged as the most discriminating traits across all stages of life.

Some of the site-level patterns were unexpected. Pouniakele, despite being the driest and most degraded site, produced trees with the largest mean diameters in every cohort. Kouassi-N’Dawa and Koumokro, by contrast, yielded trees with significantly larger leaves. In the young cohort, ten of the eleven measured variables differed highly significantly among sites, with juveniles at Kouassi-N’Dawa reaching the greatest total heights, an apparent response to light competition in the shaded sacred forest. Among non-exploitable adults, Koumokro dominated seven variables, posting the tallest mean height at 13.54 metres and the widest crown spread at 8.5 metres, while Pouniakele trees paradoxically combined the thickest trunks, averaging 33.12 centimetres, with the lowest values for six other traits.

Perhaps the most intriguing result is a reversal in the ontogenetic trajectory of diameter. Among juveniles, the gradient ran from thickest at Koumokro to thinnest at Pouniakele. By maturity, that order had flipped, with Pouniakele trees topping the rankings. The researchers interpret this inversion as evidence that the survivors at the harsh northern site prioritise radial growth to enhance mechanical stability and resource storage after episodes of water stress and pruning. Supporting this reading, the coefficient of variation for crown spread surged from 25.6 percent in young trees to 51.9 percent in exploitable adults, a signature of individual trees each following their own adaptive path through a mosaic of microhabitats and human disturbances.

The pooled analysis of all trees crystallised the picture into three site-scale morphotypes. Group 1 contained the giants of the sample, with a mean diameter of 42.9 centimetres, a total height of 14.37 metres and a crown spread of 9.53 metres, but the shortest leaves at 28.3 centimetres. Group 3 sat at the opposite pole: small trees averaging just 10 centimetres in diameter and 6.6 metres in height, yet bearing the largest leaves, up to 37.7 centimetres long. The geographic distribution of these morphotypes was anything but random. At drought-prone Pouniakele, 60.5 percent of trees belonged to the big-trunk, small-leaf Group 1, a combination that favours water conservation and mechanical resilience. At Kouassi-N’Dawa and Koumokro, where regeneration is denser and competition for light fiercer, the small-stature, large-leaf Group 3 dominated, reflecting an investment in foliar area to fuel rapid height growth in crowded stands. At Pouniakele, that morphotype was almost entirely absent, accounting for just 1.2 percent of trees.

The study’s two founding hypotheses fared differently. The first, that morphological heterogeneity would be greatest at the juvenile stage, was confirmed: coefficients of variation showed young trees to be the most variable, consistent with high initial phenotypic plasticity. The second, that natural selection would progressively filter this diversity into a converged adult form, was refuted. Even the exploitable adults remained strongly differentiated, with seven of eleven parameters differing significantly among sites. This persistence of structure into old age suggests that savanna mahogany maintains multiple viable adaptive strategies simultaneously rather than marching toward a single optimal body plan. The authors frame this as an evolutionary bet-hedging strategy, a reservoir of resilience against environmental fluctuation, though they caution that the coexistence of several phenotypic groups could also represent a transitional phase before a stable adaptive optimum emerges under recurrent disturbances such as bushfires and pruning.

The practical implications reach well beyond evolutionary theory. Because leaf length and leaflet length proved reliably discriminant at every stage, foresters now have simple, measurable phenotypic criteria for selecting superior mother trees for seed collection, a critical step for plantation development that could relieve pressure on natural stands. The identification of vulnerable growth stages also helps target protection efforts. At the same time, the authors are candid about the limits of their work. The study relies exclusively on morphology, so it cannot yet say whether the observed morphotypes reflect genetic differentiation between populations or purely environmental plasticity, and the cohort design compares different individuals rather than following the same trees over time. Combining the morphometric approach with neutral genetic markers, and mounting long-term monitoring of marked cohorts, are the obvious next steps. What is already clear, however, is that conserving this species means conserving its diversity of forms, not just its count of individuals, and that a sacred forest, a community woodland and a battered northern savanna each preserve a different chapter of the mahogany’s adaptive story.

Subject of Research: Ontogenetic variation in morphological traits of Khaya senegalensis across three savanna sites in Côte d'Ivoire

Article Title: Ontogenic dynamics of phenotypic diversity in savanna mahogany (Khaya senegalensis) across three sites in Côte d’Ivoire

Article References: Tré, B. I. G., Koffi, K. G., Kouonon, L.-C., Yao, Y. E. P., Pereda-Loth, V., & Sié, R. S. (2026). Ontogenic dynamics of phenotypic diversity in savanna mahogany (Khaya senegalensis) across three sites in Côte d’Ivoire. Discover Plants, 3(1), Article 408. https://doi.org/10.1007/s44372-026-00883-8

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00883-8

Keywords: Khaya senegalensis, savanna mahogany, phenotypic plasticity, ontogeny, Côte d'Ivoire, morphological variability, tree conservation, CITES, mother tree selection, drought adaptation, leaf morphology, sustainable forestry