An Integrated Assessment of Legume Species Diversity and Soil Characteristics in Upper Amazonian Protected Forests

Legumes (Fabaceae) are key functional components of tropical forests due to their role in nitrogen fixation and nutrient cycling. This study provides an integrated assessment of forest legume diversity and its relationship with soil physicochemical properties across three protected areas in the Peruvian upper Amazon: the Alto Mayo Protected Forest (BPAM), the Cordillera Escalera Regional Conservation Area (ACR-CE), and the Shunté and Mishollo Forests Regional Conservation Area (ACR-BOSHUMI). Floristic studies were conducted in nine sectors ranging from 618 to 1729 m a.s.l. Soil samples were analyzed, and vegetation cover was quantified using high-resolution drone imagery with four vegetation indices derived from RGB data. We recorded eleven legume species from eight genera within the sampling plots, identifying Inga as the most frequent genus. Species diversity was highest in the ACR-CE, whereas BPAM showed lower richness and abundance. Multivariate analyses revealed that legume diversity was positively associated with higher soil pH, cation concentrations, and cation exchange capacity, but negatively associated with elevated Al3+ and Fe3+ levels. Vegetation indices effectively distinguished between vegetated and degraded areas, indicating higher legume occurrence in sites with greater canopy cover. These findings emphasize that soil fertility and vegetation structure are key drivers of legume diversity, with significant implications for conservation in the upper Amazon.