Semi-natural grasslands provide many ecosystem services with biomass production for livestock being of major importance. Both plant species diversity (i.e. taxonomic diversity at the species level) and functional diversity can affect grassland productivity and ecosystem services. However, previous research has revealed positive, negative or unimodal diversity–productivity relationships in grasslands. This research focused on three different Irish semi-natural grassland habitats: dry calcareous and neutral grassland (GS1), dry-humid acid grassland (GS3) and wet grassland (GS4). Comparison of functional diversity revealed that GS1 and GS4 grasslands had higher functional richness than GS3. Classification of strategies from leaf traits according to the competitor, stress tolerator, ruderal (CSR) system showed that GS4 had the highest values for competitiveness (C) and GS3 the lowest. GS3 had higher values for stress tolerance (S) than the other two habitats, but ruderality (R) did not differ among the habitats. Based on differences found between the habitats, we tested the hypothesis that diversity-productivity relationships depend on grassland habitat type. For all habitats combined, functional diversity was positively correlated with species richness, Simpson diversity and Simpson evenness, but not for the generally species-rich GS1 grasslands. Relationships between productivity (NDVI derived from UAV surveys) and diversity were overall negative, with the most strongly negative diversity-productivity relationship found in the GS3 grassland habitat. Community-weighted means of leaf dry matter content (CWM–LDMC) and community S strategy were also negatively correlated with productivity in GS3 grasslands, but no relationship between CWM-LA or C strategy was found in any of the grassland habitats. Differences in diversity-productivity relationships in different habitats suggest that management or soil type influence the nature of these relationships, especially in stressful acid grasslands.