Developing an Original Phytogeographic Classification of the Nigerian Savanna Flora Using Multivariate Biogeographic Methods and Fossil Pollen Evidence

The phytogeographic classification of the Nigerian savanna flora has relied on qualitative vegetation zone descriptions rather than quantitative multivariate biogeographic analysis, and the integration of fossil pollen evidence to reconstruct historical phytogeographic boundaries has not been attempted, leaving significant gaps in our understanding of Nigeria's savanna floristic history. This study develops an original quantitative phytogeographic classification of the Nigerian savanna flora using multivariate biogeographic methods and fossil pollen evidence, based on a comprehensive floristic database constructed from herbarium specimen records, literature compilations, and original field surveys. The database comprises 14,820 unique species-locality records for 1,640 savanna plant species, covering the Guinea savanna, Sudan savanna, and Sahel zones. Cluster analysis, non-metric multidimensional scaling, and indicator species analysis were used to identify floristic sub-regions within the Nigerian savanna zone. Transition zone analysis quantified the sharpness of boundaries between floristic regions. Fossil pollen sequences from two sediment core sites in Borno State (Lake Chad basin) and Kogi State (River Niger valley) provided palaeovegetation data for the Holocene (last 10,000 years) to contextualise current phytogeographic patterns. Multivariate analysis identified five distinct floristic sub-regions within the Nigerian savanna rather than the three classically recognised zones, with two previously undescribed transition sub-regions identified in the middle belt. Fossil pollen evidence showed that current phytogeographic boundaries shifted northward by 80 to 120 km during the African Humid Period (approximately 9,000 to 5,000 years before present) relative to their present positions, explaining current floristic disjunctions. An original Savanna Floristic Region Map of Nigeria is produced at 1:500,000 scale. The study makes original contributions to Nigerian phytogeography and West African vegetation biogeographic history.

Keywords: phytogeographic classification, Nigerian savanna, multivariate biogeography, fossil pollen, floristic regions