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Floristic Simplification and Exotic Dominance in Human-Modified Sudan Savanna Landscapes: Implications for Biodiversity Conservation and Agroecological Resilience

Abdulrahman, A., Mansur M.A., Atiku, M., Ambursa, A.S., Muhammad, Z., Salisu, I.A., Wele H. K, Gwimmi D, ., Umar, I, ., Nafiu, A.K., Wele, H.K., F.U., Zogirma

Abstract

West African Sudan Savanna ecosystems are experiencing unprecedented anthropogenic transformation, yet empirical data on floristic restructuring within institutional and agro-pastoral mosaics remain critically scarce. This study quantified tree species composition, diversity, and structural dominance across four land-use/land-cover types within four tertiary institutions in Kebbi State, Nigeria. Using systematic plot sampling (n=120), floristic indices, and hierarchical cluster analysis, we documented species impoverishment patterns and taxonomic dominance hierarchies. Mean species richness ranged from 0.8 (bareland, RS 4) to 3.6 (built-up, RS 3), with Shannon diversity (H′) between 0.07 and 0.85, substantially lower than intact West African savannas (typically >2.0). The exotic Azadirachta indica (Meliaceae) exhibited overwhelming dominance, achieving Importance Value Indices up to 283.3 and accounting for 44.8–74.3% of carbon contributions. Cluster analysis revealed three distinct floristic syndromes: (1) Meliaceae-dominated systems (61.8% carbon contribution), (2) residual mixed- family agro-pastoral assemblages (Combretaceae-Fabaceae co-dominance), and (3) ornamental/introduced taxa in built-up zones. High evenness values (0.64–0.94) were statistical artifacts of low richness rather than ecological health indicators. Monoculture plots comprised 40–90% of sampled areas, with treeless plots occurring in 10–30% of farmlands and barelands. The documented floristic impoverishment signals advanced landscape simplification and loss of functional redundancy. These findings challenge assumptions that institutional landscapes serve as biodiversity refugia and underscore the urgent need for native species enrichment, farmer- managed natural regeneration, and policy frameworks that prioritize taxonomic diversity alongside carbon metrics in climate-smart land management.

Keywords

Biodiversity lossAzadirachta indicafloristic homogenizationinstitutional landscapesSudan SavannaWest Africa

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