Caracterización anatómica y peso específico de la madera de las dos especies leñosas nativas más frecuentes en el área protegida “Esteros y Blanqueales del Río Uruguay” Neltuma nigra (Griseb.) C.E. Hughes & G.P. Lewis, comb. nov. y Schinus longifolia (Lindl.) Speg.

Introduction: This study examined the quantitative and qualitative anatomical characteristics of the wood in two native species, Neltuma nigra (Algarrobo) and Schinus longifolia (Molle). The research had place in the conservation area "Esteros y Blanqueales del río Uruguay" at the Mafalda establishment of United Paper Mills – UPM – Forestal Oriental, in Quebracho, Paysandú, Uruguay.

Methodology: Dendrometric measurements were recorded from individuals present in selected plots within the conservation area. Cores were extracted using a Pressler borer and processed in the laboratory according to Wheeler et al. (1989). Vessel diameter and length, fiber length and width, vessels per mm², dimensions and frequency of parenchymatic rays were measured. Crystals and fiber-tracheids were also identified, and the basic apparent specific gravity was calculated using Archimedes’ principle. For S. longifolia, as it was the first recorded study, the data were compared with those of other species of the genus Schinus, showing similarities with S. molle: vessels of 232.0 µm in height, 34.6 µm in width, 162.7 vessels/mm² and average density of 0.82. Rays measured 262.9 µm in length and 26.2 µm in width; fibers, 683.5 µm in length by 17.0 µm in width. N. nigra presented vessels of 149.8 µm in length and 117.0 µm in diameter, with 15 vessels/mm²; fibers of 911.2 µm in length by 14.4 µm in width. Rays measured 370.1 µm in length and 67.5 µm in width, with a frequency of 5.3 rays/mm. Rhombohedral crystals were observed in parenchymatic cells and an average basic density of 0.83 g/cm³ was obtained, classified as heavy wood.Final del formulario

Results: The study reveals that both species have high density, suggesting their potential as high-quality structural wood. Further research will generate a better understanding of their properties and applications. Additionally, density analysis is crucial for making more accurate biomass estimates, which could have significant implications for ecological studies and forest management. The comparison of anatomical characteristics between species from different regions of South America, in the case of N. nigra, allowed for a deeper understanding of the relationship between these properties and geographic locations, enriching knowledge about biodiversity and species adaptation within the same habitat. This study represents the first anatomical characterization of S. longifolia, while findings regarding N. nigra indicate that its properties are comparable to those of other populations in the Argentine Chaco. Together, these results contribute to the understanding of anatomical variability within the regional ecological context and open new avenues for future research.