Intraspecific trait variability is pivotal for plants to overcome environmental filters, shaping the species distribution and abundance in heterogeneous landscapes such as ecotonal zones. In this study, we aimed to understand the role of intraspecific trait variation on species occupation in a sharp ecotone. For this, we used, as a model, a dominant tree species of forest-savanna transitions in Brazil's Southwest and focused on stem architecture and allometries and leaf functional traits. Our results showed that trait variability improves plant performance along the ecotonal gradient. In fact, trees in forest optimize the light-interception and -use by the production of tall and slender stems and more acquisitive, smaller, and thinner leaves. On the other hand, trees in savannas had the opposite morpho-functional pattern, enhancing their resistance to wind, drought, continuous light incidence, and nutrient-poor soils. Surprisingly, trees right at the forest-savanna transition resembled forest tress regarding shoot morphology and savanna trees regarding leaf functional traits. However, displaced crowns were a singularity of transition trees. Taken together, our study shows that intraspecific variability is crucial for a dominant plant to successfully occupy contrasting habitats along the forest-savanna transition. Our study thus highlights the importance to investigate the role of intraspecific trait variation to better understand species dominance and community assembly in ecotonal zones.