Methods & Validation
Scientific approach and validation framework for the Research-Based Monte Carlo model.
Chapman-Richards Growth Model
Asymptotic growth trajectory
Asymptote values sampled from priors with species-specific distributions
Growth rate constants (k, c) vary by species and site conditions
Asymptote uncertainty is applied via clipped z-scores to create parallel growth trajectories. This captures both parameter uncertainty (asymptote values) and structural uncertainty (growth rate constants).
Self-Thinning Density Dynamics
Size-density feedback
Calibrated to anchor mixed stands to sampled dy40 target
Default 1.6 controls self-thinning strength
Quadratic mean diameter drives density limits
α is calibrated so mixed stands anchor to the sampled dy40 target while respecting species-specific density limits. The beta parameter (default 1.6) controls the strength of self-thinning.
Allometry Weighting
Structural equation uncertainty
Primary equations: West African allometry (Zanvo et al. 2023, Benin) calibrated to Niger Delta conditions. Weighted sampling captures structural uncertainty across regional equation sets, yielding approximately 50% lower (more conservative) biomass estimates than global IPCC equations.
Dependence Structure
Shared latent site quality factor
A shared latent factor induces realistic correlation across growth, SOC, and density. This ensures biological coherence: high-quality sites have both better growth and higher soil carbon accumulation.
Model Validation
Conservative vs field measurements
Model vs Literature
Growth model projections at 30 years are 1–9% lower than weighted-average values from literature, validating realistic size trajectories.
Model vs Nigerian Field Data
Model projections are 29–68% more conservative than actual measured growth from 3 Nigerian pilot sites (1.5–2 year monitoring). This conservatism is appropriate for ex-ante projections submitted for certification.
Validation approach: Model conservatism is validated against both regional literature benchmarks and direct field measurements from pilot restoration sites in the Niger Delta. The conservative bias ensures credible ex-ante carbon estimates suitable for carbon credit certification.