Beyond the forest: terrestrial snails as bioindicators of Afromontane deforestation and land-use change

Tropical Afromontane forest is experiencing rapid deforestation and land-use change, threatening biodiversity in one of the world's richest ecosystems. In Rwanda's Gishwati–Mukura landscape, primary forest has been largely replaced by agroforestry systems, tea plantations, and exotic tree monocultures. Using land snails as bioindicators, we investigated species richness, diversity, and community composition across seven land-use types and five levels of surface degradation. A total of 3235 individuals representing 118 species were sampled from 173 plots using standardized litter and soil collection. Primary forest harbored the highest species richness and diversity, followed by Alnus plantations, while Eucalyptus, Pinus , and tea plantations supported impoverished communities. Species richness (Hill number q = 0) and Shannon diversity (Hill number q = 1) declined significantly with increasing surface degradation. Assemblage composition was strongly influenced by land-use type and environmental variables, particularly leaf litter depth and distance to the nearest protected area. Non-metric multidimensional scaling showed that Alnus plantations clustered closely with primary forest, indicating structural and compositional similarities. In contrast, other plantation types and home gardens showed greater internal heterogeneity and supported more generalist or disturbance-tolerant species. Morisita–Horn similarity indices revealed that species dominance patterns also varied across land-use types. Our results highlight the ecological importance of remnant primary forest and show that although Alnus plantations can support land snail diversity and assemblage composition comparable to primary forest, they exhibit a markedly different dominance structure. This finding reinforces the need to move past traditional species-level metrics when evaluating land-use change, incorporating additional parameters such as species assemblage composition and dominance structure. Effective conservation in the Gishwati–Mukura landscape should prioritize protecting remaining forests while promoting restoration strategies that enhance microhabitat quality and sustain native biodiversity.