The present study was carried out with the objective of knowing the dynamics of summer survival of perennial C3 grasses in subtropical environments under a microclimate modified by the tree component. Three species grown in conditions of full sun and silvopastoral systems (SPS) (Dactylis glomerata, Festuca arundinacea and Holcus lanatus) were evaluated, with the hypothesis that the persistence of C3 summer grasses in SPS depends on the ability of the genotype to adapt to the understory microclimate. Forage species were evaluated under tree treatments: two forests with 20 m wide alleys, oriented North-South (NS), East-West (EW) and full sun. The population density of tillers (tillers.m-2) at the beginning of the summer for Dactylis, Fescue and Holcus respectively was 1.933, 2.867 and 2.156 in NS; 2.289, 3.044, 2.567 in EW and 3.017, 4.500, 4.667 under full sun. The values for the same variable at the end of the study (March) were 2.633, 1.644 and 22 (NS); 2.056, 944 and 0 (EW); 1.750, 3.317 and 533 under full sun (P <0.05). The results showed that the mortality of Fescue tillers accelerated when the amount of light was reduced. Holcus showed higher mortality throughout the summer, with an increase below the forest. Dactylis was more persistent below forests, especially in the N-S, showing it could be a promising species for SPS.