Key message Oak species displayed high interspecific functional trait variation. The resource use strategy among oaks both at the above and belowground organs was guided by the fast-slow continuum. Plant functional ecology has focused on the study of functional strategies and general patterns of trait covariation. Mostly, studies intend to elucidate how plants cope with resource capture both at the above and belowground organs and to understand how the capacity for resource gain relates with the species distribution. American oaks are an interesting and important tree clade, they radiated into diverse environments outside temperate regions implying the development of adaptations to persist under different environmental regimes. Therefore, we explored patterns of differentiation in functional traits related with the capacity for resource use in 3-month seedlings of ten Mexican oak species representative from semiarid, temperate and subtropical montane regions. We examined the fast–slow trade-off and its importance in species differentiation on both above and belowground organs. Additionally, we investigated how resource acquisition strategy of the species was related with the environmental conditions experienced in their habitats. We found a significant differentiation in both above and belowground traits, and in both cases oak species segregated along the fast–slow continuum. We found only a few significant trait-by-trait relationships, implying a weak coordination among aerial and subterranean organs. Additionally, species from sites with higher precipitation seasonality had a higher root growth, and species from humid sites had larger leaves. These findings highlight important functional variation among oak seedlings which was related with the climatic conditions encompassed along their native geographic range.