Assessing Dioscorea spp. Distribution and Abundance in the Comoros and Management Implications

Abstract

Yam species (Dioscorea spp.) are of major economic, ecological and cultural importance in the Comoros, where the genus is particularly diverse. However, several native species are in decline, potentially due to a combination of ecological constraints and increasing anthropogenic pressures. This study used species distribution modelling (SDM), direct population counts and linear models to assess habitat suitability, abundance and their relationship with ecological and soil-related variables for three yam species: the Comoros-endemic D. comorensis, the regional endemic D. sensibarensis and the widely cultivated D. alata. Dioscorea comorensis showed strong habitat specificity, being confined to intact native forests with minimal disturbance, with only 56 individuals recorded across the island. Its abundance was positively associated with natural forest cover and negatively with agriculture and urban areas. D. sensibarensis was found in both natural and degraded vegetation, with an intermediate population size (266 individuals), and its abundance also declined in areas with high human activity. In contrast, D. alata exhibited a broad ecological amplitude, occurring in farmlands, village landscapes and degraded habitats. Its abundance (345 individuals for the Cameroon variety and 690 for the Comoros variety) was positively correlated with agricultural land use and human-modified areas. The results highlight clear ecological niche differentiation among the three species and stress the importance of land-use patterns in shaping yam abundance. Conservation priorities should include (1) preserving native forests to support rare endemic species, (2) limiting secondary forest conversion to maintain semi-endemic populations and (3) promoting agroforestry systems for sustainable cultivation of introduced species.