Relationship Between Forest Structure and Soil Characteristics with Flooded and Non-Flooded Rainforests of Northern Amazonia (Brazil)

Environmental variability modifies forest structure through interactions among soil properties, topography, and climate. These factors influence the occurrence of contrasting forest types in northern Amazonia (Brazil), such as forests in highlands (Terra Firme) and forests under regular flooding (Várzea). Flooding regimes influence soil formation and modify soil geochemistry, nutrient distribution, and organic matter accumulation, shaping forest structure and composition. The objective was to determine the relationships between structure and soil characteristics in non-flooded and flooded tropical forests. We compared forest structure and soil characteristics at both conditions (n = 2 treatments × 20 replicas = 40 plots) using univariate and multivariate analyses. We found significant differences in most of the studied variables between forest types, both chemical and physical properties. Our results showed that flooding defines forest structure and composition (e.g., tree density, height, and volume) and influences soil nutrient characteristics. Floodplain forests exhibited higher soil nutrient concentration and organic carbon content, likely due to periodic litter accumulation, sediments, and reduced decomposition rates. In contrast, non-flooded forests were characterized by lower nutrient levels, higher sand content, and greater forest structure values (e.g., height, basal area, and volume). These insights contribute to understanding the functioning of both forest ecosystems.