Floristic diversity, structural dynamics, and conservation status of the Ambatolahy forest reserve : Implications for community-based management in Madagascar

ABSTRACT This study evaluates the floristic composition, structural dynamics, and conservation value of the Ambatolahy Forest Reserve in Madagascar to assess its ecological integrity within the broader Ranomafana landscape. A comprehensive inventory revealed 83 woody species across 42 families, characterized by high diversity indices (Shannon = 4.146 ; Margalef = 13.124), indicative of a mature and stable ecosystem. Structural analysis showed a classic inverted J-shaped diameter distribution, confirming robust natural regeneration, although a deficit in large-diameter stems (> 40$ cm) suggests historical selective logging. Importance Value Index (IVI) analysis identified Ocotea sp., Grewia spp., and Streblus dimepate as keystone species driving the forest's architectural complexity. Conservation assessment according to IUCN criteria revealed that 16% of the identified taxa are threatened or vulnerable, underscoring the reserve’s role as a critical refugium for endemic flora. Multivariate hierarchical clustering further delineated four ecologically coherent species groups based on density and basal area, reflecting specialized niche partitioning and successional stratification. Edaphic analysis highlighted acidic, erosion-prone soils, reinforcing the protective necessity of the forest cover. These findings validate the reserve’s resilience and emphasize the importance of community-based adaptive management for mitigating anthropogenic pressures and preserving regional biodiversity. Key words : Biodiversity conservation, floristic structure, inverted J-curve, IUCN status, Ranomafana landscape.