The Importance of the Araguaia Basin in Maintaining Forest Structure, Physiognomic Patterns, and Edaphic Heterogeneity

Riparian vegetation in the Araguaia basin remains poorly studied, with few forest inventories addressing its structure and composition. This study sought to integrate attributes of tree communities along the upper, middle, and lower reaches of the basin, evaluating their physiognomic organization and their relationships with edaphic characteristics, aiming to verify the differences between these three regions of the Araguaia River basin. We hypothesize (1) that the structuring and composition of the riparian vegetation community of the different regions of the Araguaia are influenced by different vegetation domains (biomes) and, consequently, the longitudinal gradient of the basin. As a secondary hypothesis (2), we also point out that forest attributes are influenced by edaphic attributes, with the patterns presented by the vegetation being affected by soil characteristics such as fertility and soil physics. We conducted inventories in 27 sites, measuring forest structure, composition, and soil properties. To compare vegetation parameters across locations and with soil characteristics, various analyses were performed, including CCA, PCA, the ANOSIM test, and GLM followed by Tukey’s test. A total of 405 individuals were recorded, belonging to 48 families and 152 species. Fabaceae was the most abundant family, followed by Rubiaceae, Simaroubaceae, and Anacardiaceae. Genera such as Aspidosperma, Andira, and Casearia were particularly diverse. Soil pH and potassium were the main edaphic factors that differentiate vegetation, being evident between gallery forests and cerradão formations. Cerradão areas generally exhibited lower diversity and more acidic soils, while gallery forests showed higher fertility and species richness. Regarding forest composition, the variables that showed significance in the CCA were Ca, Al, and clay. The species were associated with three main edaphic groups. We can highlight species from forest formations associated with soil clay content (Copaifera langsdorffii, Ixora gardneriana, Aspidosperma discolor, Siparuna guianensis, Virola sebifera); a second group consists of riparian forest species associated with aluminum levels (such as Myrsine guianensis, Mabea sp., Alchornea castaneifolia, Vochysia pyramidalis). The third group did not correspond to a specific vegetation formation but comprised species associated with calcium levels, species known not to be associated with water (Matayba guianensis, Handroanthus heptaphyllus, Luehea sp., Anadenanthera colubrina, Piptadenia gonoacantha, Guarea guidonia, Senegalia polyphylla, Curatella americana, Guazuma ulmifolia, Astronium urundeuva, and Rhamnidium elaeocarpum). The ecological heterogeneity of riparian vegetation in the Araguaia basin emphasizes the importance of soil attributes in shaping forest communities, providing baseline information for conservation strategies, reinforcing the need to consider both ecological and edaphic factors in management plans for riparian ecosystems in the Cerrado and Amazon transition zones.