Facing West Africa's rosewood crisis: what determines the success of preserving and propagating the endangered barwood (Pterocarpus erinaceus)? A multi-model test of site and maternal-origin effects

Pterocarpus erinaceus Poir. (Fabaceae), the barwood or vene, is at the heart of one of the most severe conservation crises currently affecting tropical timber species. It has become the most heavily traded timber species in the world by volume, at the centre of an illegal rosewood trade to Asia that has driven the species to near-total disappearance in several countries despite its listing on CITES Appendix II since 2016. Faced with this urgency, ex situ conservation and restoration programmes often rest on the untested assumption that selecting seed trees by size improves the quality of the offspring produced in the nursery. This study rigorously tests this hypothesis against the competing one of a determinism dominated by the planting site, using six complementary analytical approaches (continuous regression, linear mixed models with a site x seed-tree interaction, seed-mass mediation analysis, non-linear growth modelling of height and diameter, between-site phenotypic plasticity, and multi-predictor allometric equations), across two contrasting bioclimatic sites in COte d'Ivoire (Korhogo: dry zone; Daloa: humid zone) and six seed-tree categories. Site exerts a decisive influence on growth at all ages (ANOVA, p<0.001 for height, diameter and biomass), whereas germination does not differ significantly between sites (70.3% at Daloa versus 61.6% at Korhogo; X2=1.95; p=0.162). Seed-tree DBH does not affect growth in any of the tests (continuous regression, p>0.30; mixed model, p>0.07), and the seed-mass mediation analysis remains inconclusive, seed mass varying only slightly among seed trees in this species (0.07-0.08 g). The exponential growth model provides the best fit for height and diameter at both sites, and two-predictor allometric equations explain 96.2% of biomass variance compared with 89.9% for the single-predictor model. These results indicate that ex situ conservation and compensatory reforestation programmes for this endangered species would benefit from prioritising the choice of planting site over the dendrometric selection of seed trees. A recommendation directly applicable to conservation nurseries established in response to the rosewood crisis.