Aboveground Biomass and Carbon Stocks Across Four Contrasting Vegetation Units in Sierra del Divisor National Park, Peru: Structural Attributes Outweigh Taxonomic Diversity

Amazonian forests store large amounts of carbon, but storage capacity varies widely with topography, hydrology and successional stage. We quantified aboveground biomass (AGB) and carbon stocks across four vegetation units in the Tacshitea sector, Sierra del Divisor National Park (Peru): semi-dense flooded forest (Z1), hill forest (Z2), hill forest associated with secondary growth (Z3), and Mauritia flexuosa palm forest (Z4). In each unit we established a contiguous 5 × 5 grid of 20 × 20 m plots (25 plots, 1 ha sampled per unit) and assessed all individuals with diameter at breast height (DBH) ≥ 10 cm, using allometric equations validated for Amazonian ecosystems. A total of 2363 individuals belonging to 156 species from 41 families were recorded. Aboveground biomass differed markedly among vegetation units, with the highest values in Z1 (401.15 Mg ha−1; 188.54 Mg C ha−1) and Z2 (328.92 Mg ha−1; 154.59 Mg C ha−1), whereas Z3 and Z4 recorded substantially lower values (142.25–144.53 Mg ha−1; 66.86–67.93 Mg C ha−1). The Fabaceae family dominated carbon storage at the landscape scale (34.7%). Comparing predictor blocks directly at the plot level, structural attributes explained 92.4% of the variance in carbon stock against 5.6% for taxonomic diversity (ΔAIC = 248), and variance partitioning attributed 87.3% exclusively to structure and 0.5% exclusively to diversity, indicating that basal area, wood density and stem size are far more robust predictors of storage capacity than taxonomic richness per se. Beta diversity analysis revealed that floristic differentiation among zones was dominated by species turnover, explaining 26.5% of the variation by vegetation unit (PERMANOVA, F = 11.54; p = 0.001), although within-unit dispersion was heterogeneous, so part of that signal reflects differences in internal variability rather than centroid position alone. Because each unit was sampled as a single contiguous block, unit effects are confounded with location, and the comparisons describe the four stands evaluated at Tacshitea rather than the vegetation types they represent. These results support the relevance of Sierra del Divisor National Park as a carbon reservoir in the western Peruvian Amazon and underscore the necessity of conservation strategies that integrate the structural heterogeneity of the forest mosaic.