PREDICTING STRENGTH FROM DENSITY IN SELECTED AFRICAN TIMBERS: ACCURACY AND SENSITIVITY OF SIMPLE MODELS

Methods: Thirteen reference means from Tropix (CIRAD, 2023-2026), spanning 380-1060 kg/m3, were analysed. Proportional, affine and power models were compared with a mean-only baseline using internal leave-one-out and leave-one-genus-out cross-validation. Twelve genera were represented, with only one repeated genus. Deterministic deletion scenarios and influence diagnostics assessed sensitivity. Results: The proportional model achieved internal genus-out RMSE values of 8.96 MPa in bending and 2.97 MPa in compression, equivalent to 9.47% and 5.27% of the respective mean responses. These are errors against held-out documentary means, not laboratory measurement uncertainties or specimen-level prediction errors. Relative to the mean-only baseline, RMSE decreased by 73.2% and 84.4%. Density remained informative across the examined deletion scenarios, although model-form rankings could reverse.