Mapping Functional Diversity of Savanna Trees and Its Relationship to Ecosystem Productivity in Kano State, North West Nigeria

Functional diversity of plant communities links biodiversity to ecosystem process rates and productivity, yet this relationship has rarely been quantified in West African savanna systems. This study mapped functional diversity of savanna trees and examined its relationship to above-ground net primary productivity in Kano State dry savanna. Sixty study plots were established across a gradient of tree cover and land management intensity. Tree species composition and abundance were recorded, and functional traits including leaf dry matter content, specific leaf area, wood density, maximum height, and seed mass were measured from collected specimens and supplemented from published trait databases. Community-weighted means and functional diversity indices were calculated for each plot. Above-ground net primary productivity was estimated from Normalised Difference Vegetation Index time-series data corrected for rainfall. Structural equation modelling was used to test pathways linking tree species richness, functional diversity, and productivity. Results showed that functional diversity indices explained significantly more variation in productivity than species richness alone, consistent with the complementarity hypothesis. Community-weighted mean wood density emerged as the strongest single functional trait predictor of productivity, reflecting the importance of slow-growing, dense-wooded species in productivity stability. Heavily grazed plots showed reduced functional diversity and lower productivity. The study recommends incorporating functional diversity metrics into ecosystem health assessments for savanna conservation and restoration planning in North West Nigeria. Keywords: functional diversity, savanna trees, Kano State, ecosystem productivity, plant traits.