Tree Allometry and Structural Inequality in Two Neotropical Forest Stands with Contrasting Hydroclimatic Settings

Tropical forests occupy hydroclimatic settings ranging from nearly continuous rainfall to pronounced seasonal water limitation, yet the ways in which these contrasting settings coincide with tree allometry, structural inequality, and carbon storage remain incompletely understood. We compared a tropical wet forest in Santa Ana, Colombia (SA), with a tropical semi-deciduous forest in Tomatlán, Mexico (TO), using 1991–2020 climatological normals and inventories of 611 and 392 stems, respectively. Floristic diversity, stand structure, height–diameter allometry, Gini-based inequality, large-tree contribution, biomass, and carbon stocks were evaluated. Aboveground biomass was estimated using DBH, total height, and species- or genus-level wood density, while palms were treated separately using a growth-form-specific equation. SA received 8233.4 mm yr−1 and had no dry months, whereas TO received 726.4 mm yr−1 and had seven dry months. SA supported greater species diversity and taller trees across the shared DBH range, while TO had greater stem density, mean DBH, basal area, biomass, and carbon stocks. AGB was 31.54 Mg ha−1 in SA and 84.79 Mg ha−1 in TO. The largest 10% of stems accounted for 39.26% of AGB in SA and 54.77% in TO. Basal area was the structural attribute most strongly associated with AGB in both forests. These findings show that the two stands differed in structural organization and biomass concentration rather than following a simple increase in carbon storage with rainfall. Because each hydroclimatic setting was represented by a single forest, the results describe a paired stand comparison and should not be interpreted as a causal test of climatic effects.