Context-dependent effects of habitat type and grassland fragment size on bird diversity in European and African grassland-forestry mosaics

Abstract

Habitat loss and fragmentation are primary drivers of terrestrial biodiversity decline, but their effects may vary substantially across biogeographic regions and landscape contexts. We investigated how habitat type and grassland fragment size influence bird communities in two contrasting grassland ecosystems: the Pannonian sand forest steppe in Hungary and mist-belt grasslands in South Africa. Using parallel study designs, we surveyed birds in 18 natural grassland fragments spanning a range of sizes in each study region, each paired with an adjacent non-native plantation forestry site. In Hungary (43 species), we found no significant differences in species richness or abundance between natural grassland fragments and adjacent pine plantations, regardless of grassland fragment size, though community composition differed between habitat types and varied with grassland fragment size. In contrast, South African landscapes (109 species) suggest dramatic biodiversity loss in the extensive forestry plantations for both richness and abundance and showed a significant effect of habitat type on community composition. These contrasting patterns reflect fundamentally different relationships between biodiversity and landscape structure across biogeographic contexts. In Hungary, the small-scale plantation habitat mostly maintained bird diversity. Conversely, South Africa's extensive plantation habitat largely displaced bird communities, with biodiversity concentrated in remaining natural grassland fragments. Our results demonstrate that effective conservation in fragmented landscapes requires regionally tailored approaches that account for biogeographic context and the scale of anthropogenic modification.