ANALISIS KEANEKARAGAMAN JENIS PENYUSUN VEGETASI DI KAWASAN MANGROVE KABUPATEN SIMEULUE

Mangrove forests are important coastal ecosystems that support biodiversity, shoreline protection, carbon storage, and the livelihoods of coastal communities. This study aimed to analyze the species composition, vegetation structure, Importance Value Index (IVI), and species diversity of mangroves in West Simeulue District, Simeulue Regency, Aceh. Vegetation data were collected in December 2025 using purposive sampling at 12 main plots of 10 m × 10 m, with nested subplots of 5 m × 5 m and 2 m × 2 m for saplings and seedlings, respectively. The observed variables included species identity, number of individuals, height at the seedling stage, and stem diameter at the sapling and tree stages. Vegetation structure was described using density, frequency, basal area, relative density, relative frequency, relative dominance, and IVI, while species diversity was evaluated using the Shannon–Wiener index (H′). A total of 234 individuals representing nine species and six families were recorded. Rhizophora apiculata and Rhizophora mucronata were the dominant species and occurred across the major growth stages. At the tree stage, R. mucronata had the highest IVI (118.10), followed by R. apiculata (113.92). At the sapling stage, R. apiculata had the highest IVI (70.65), whereas at the seedling stage it also showed the highest IVI (120.27). The Shannon–Wiener diversity index was 1.217 for trees, 1.489 for saplings, and 0.684 for seedlings, indicating moderate diversity at the tree and sapling stages and low diversity at the seedling stage. The high abundance of seedlings indicates that regeneration is occurring, but the strong dominance of Rhizophora suggests that regeneration is compositionally uneven. These findings provide a baseline for site-level monitoring and support the need for conservation and restoration strategies that maintain natural regeneration while protecting less abundant mangrove species