Past, present, and future distribution of Paspalum notatum Flüggé reveals South American grassland dynamics

Abstract

South American grasslands harbour remarkable biodiversity shaped by complex evolutionary and climatic histories, yet their dynamics and responses to ongoing climate change remain poorly understood. We used the widespread C4 Paspalum notatum as a model to investigate the spatio-temporal dynamics of these grasslands. We aimed to (i) determine its cur¬rent potential distribution and key environmental drivers, (ii) reconstruct shifts since the Last Glacial Maximum (LGM) to identify stable refugia, and (iii) project potential future range displacements. We combined species occurrence records with bioclimatic and edaphic variables applying the MaxEnt algorithm to model distributions for past, present, and future conditions using two global climate models and three Shared Socioeconomic Pathways (SSPs). P. notatum ranges from Mexico to Argentina and the Caribbean, with notable absences in the Amazon Basin and southern South America. Its dis¬tribution is influenced by annual mean temperature, precipitation of the driest month, isothermality, soil pH, clay content, and cation exchange capacity. Historical reconstructions showed maximum expansion into Amazonian regions during the LGM, followed by a Holocene contraction due to forest expansion, resulting in current stable refugia in southern Brazil, eastern Paraguay, northeastern Argentina, and Uruguay. Future projections consistently indicate a southward and westward range shift. Our findings reveal the remarkable ecological plasticity of P. notatum and underscore the role of Pleistocene climatic oscillations in shaping grassland composition. They highlight the conservation value of southern refugia and sug¬gest that future range shifts of this C4 species could alter the botanical composition of temperate grasslands.