The Río de la Plata grasslands (RPG) in South America are one of the largest temperate grasslands regions of the world. This region plays a key role in international crop production and land use change rates in some areas are among the highest detected nowadays. Our objective was to characterize the spatial heterogeneity of land use change dynamics in the RPG and to relate it with biophysical and political boundaries. Based on Landsat imagery we characterized land use changes at two time periods (1986–1990, 2002–2005) and we performed a comparison of markovian models and their properties (stable proportion vector and sensitivity analysis) for each phytogeographic district and country of the region. Temporal transitions between natural and implanted forests (Fo), crops (Cr), and grasslands (Gr) were calculated in order to build matrix probabilistic models. We found that 1.2 × 106 ha of grassland surface has been transformed into implanted forests and croplands (6% reduction of grasslands, 60% increase of afforestations, 3% increase of croplands). Transition probability Cr → Cr displayed the largest spatial variation, followed by the other three transitions linking croplands and grasslands (Cr → Gr, Gr → Gr, Gr → Cr). The less variable transition rate among districts was Cr → Fo.