Population Structure and Regeneration Dynamics of the Endangered Ebony (Diospyros celebica Bakh.) Across Distinct Ecological Gradients in South Sulawesi, Indonesia

Diospyros celebica Bakh. is an endangered Sulawesi endemic increasingly confined to fragmented, selectively logged forests, yet its population demography across natural habitats remains poorly known. This study quantified population structure, regeneration dynamics, and species associations of D. celebica along edaphic and disturbance gradients in three natural stands in South Sulawesi (Maros, Barru, Sidrap). Vegetation was sampled using belt transects with nested quadrats across four life stages (seedlings, saplings, poles, trees) and analysed using phytosociological indices, important value index (IVI), diversity metrics, soil properties, and chi-square association tests. In Maros, ebony showed strong dominance in tree and pole layers and substantial juvenile representation, forming a size class distribution closely approximating a reverse J-shaped curve (power regression: y = 711.98x^-2·668), indicative of continuous regeneration under moderately acidic, organic-rich soils. Barru exhibited extremely dense seedlings but sharp declines at sapling and tree stages (y = 2312.7x^-2·114), coinciding with more acidic, low-organic soils and intense competition from shade-tolerant palms. In Sidrap, ebony remained the main canopy species but was strongly underrepresented in juvenile strata (y = 605.8x^-1·158) dominated by other tree taxa, signalling an aging, demographically eroding population. Site-specific association patterns, particularly negative relationships with dense understorey palms, highlight biotic filters on early regeneration. These findings support differentiated conservation strategies tailored to each stand type to secure the long-term persistence of D. celebica in South Sulawesi’s tropical forests.