A study was conducted on the diameter structure and species diversity in a low terrace forest, in cutting plot 04 (PC 04) of the General Forest Management Plan (PGMF) for the forest concession 16-LOR-MAR/CON-MAD-2019-013, located in the district of Yavarí, Loreto. In plot 1, 38 species from 19 families and 34 genera were identified, with 518 individuals. The highest density was concentrated in the diameter classes of 10 cm (122 trees, 23,5%) and 50 cm (279 trees, 53,9%). In plot 2, 31 species from 18 families and 29 genera were recorded, with 389 individuals, with the highest density in the 50 cm class (211 trees, 54,2%). The Shannon-Wiener index (H′) was 3,09 in plot 1, indicating moderate to high diversity, dominated by Otoba glycycarpa (13,5%) and Eschweilera albiflora (12,5%). In plot 2, H′ was 2,88, reflecting moderate diversity, dominated by Otoba glycycarpa (16,7%) and Eschwe...