The influence of the type of management applied for centuries on vegetation understory has still been underexplored in semi-arid forests. We have studied how the vegetation composition, diversity and heterogeneity were influenced by two forest systems in mature semi-arid oak forests of western Iran: abandoned coppices with standards (CS) which were traditionally intensively used and old stands naturally regenerated from seeds or 'standard system' (SS). Woody and herbaceous species abundance and cover were measured in sixty plots distributed in the two forest systems. Vegetation data were used to produce Shannon's diversity, richness and Pielou's evenness indices as well as species abundance distribution (SAD) models. We found that richness and Shannon diversity values were higher in (SS) than in (CS) for both herbaceous species (43% and 27%, respectively) and woody species (27% and 52% respectively). The two main woody species of the study and several herbaceous species were present only in SS. These results emphasized the positive role played by the long-term stable conditions of SS on plant diversity. In contrast, legacy of past disturbances in CS still negatively influenced vegetation diversity although the recovery rate after the cessation of disturbances differed between the two growth forms (herbaceous and woody). This also explained a higher vegetation heterogeneity in CS than in SS for the herbaceous species, while there was no difference for the woody species. We also showed that the best SAD model for herbaceous species included the dominance decay model in CS indicating the decreased influence of the dominant oak species in CS compared to SS. In conclusion, we showed that even after more than half a century of abandonment, CS stands still differed from SS stands in terms of vegetation composition and sheltered a lower plant diversity and richness for both herbaceous and woody species. This finding highlights the need to use complementary management measures in CS to accelerate the recovery process in particular for woody species.