Patterns of Composition, Richness and Endemicity of Cyperaceae Across Open and Closed Habitats in Madagascar's Central Highlands

Abstract

The Cyperaceae family, with over 5,600 species, is a major component of open ecosystems worldwide. In Madagascar, where open grassy ecosystems dominate, the family remains understudied. We assessed Cyperaceae species composition, richness and endemicity across closed (forest), dry open (dry grasslands, rocky outcrops, bare dry soils), and wet open (marshes, swamps, wet grasslands, riparian areas) habitats in Isalo National Park and the Itremo Massif Protected Area, both in Madagascar's Central Highlands. Fieldwork spanned 40 days during which Cyperaceae specimens were collected along survey routes. Soil samples were collected from 20 habitats (5 closed, 6 wet open, and 9 dry open) and analysed for pH, nitrogen, soil organic carbon, potassium and phosphorus to evaluate their influence on species composition via co-inertia analysis. We recorded 108 species across 12 genera, 28 of which are endemic to the island. The highest richness and number of endemics were found in the dry open habitat (72 species, 20 endemics), followed by the wet open (60 species, 7 endemics). Closed habitat had the lowest number (14 species) but a higher endemism rate, with 7 endemic species. Species composition was most similar between wet open and dry open habitats (β_SOR = 0.5), and least similar between closed and dry open habitats (β_SOR = 0.91). Soil characteristics did not differ significantly among habitats, except for potassium, and they did not affect species composition. The results highlight the importance of the Central Highlands for Cyperaceae, as they are home to at least a third of native Cyperaceae species in Madagascar.