Coexistence of understory tree species via architecture differentiation in the Atlantic Forest of southern Brazil

Resource allocation, plant architecture, and ontogenetic differences are important axes of niche differentiation that promote plant species coexistence in tropical forests, contributing to the high diversity observed in these ecosystems. To test the predictions of species coexistence, differences in tree architecture were compared in a seasonal, semi-deciduous forest throughout the developmental stages. Four 3000 m ² stands with canopy cover higher than 90% were established in a protected area in southern Brazil. All individuals from three understory species were identified, and their diameter, height, and crown were measured, and comparisons in the architecture of species were made with height-class specific allometric relationships. Inga marginata invested primarily in vertical growth, with pronounced development of crown area and plasticity in crown morphology only in the last height class, while Sorocea bonplandii invested more in lateral growth to ensure mechanical stability, reducing the likelihood of trunk breakage. The same was observed in juveniles of Actinostemon concolor , which maximized investment in crown development after reaching a certain height. Although only three understorey species were studied, understanding how these species coexist is important for providing valuable insights into the mechanism of species coexistence in tropical ecosystems. Despite their location in the understorey stratum, these species play critical roles in structuring and maintaining species diversity in the forest. Focused studies on a smaller number of species can help to understand the underlying mechanisms that regulate coexistence and provide important information for the management and conservation of biodiversity in tropical ecosystems.