Unravelling the Drivers of Functional Plant Trait Diversity in the Nigerian Rainforest: An Original Contribution to Tropical Forest Ecology Theory

Functional plant trait diversity in tropical rainforests is theoretically linked to ecosystem processes including productivity, decomposition, and resilience, yet the relative importance of environmental filtering, competitive interactions, and stochastic assembly in structuring functional trait space has not been investigated for West African rainforest communities, leaving a fundamental gap in tropical forest ecology theory. This study unravels the drivers of functional plant trait diversity in the Nigerian rainforest using an original multi-scale, multi-trait empirical framework applied across 120 vegetation plots distributed across the Cross River, Ondo, and Edo State rainforest belt. Six key functional traits were measured from 210 species: leaf nitrogen content, specific leaf area, leaf dry matter content, wood density, seed mass, and plant height. Community-level weighted mean traits and functional diversity metrics (functional richness, functional evenness, and functional divergence) were calculated for each plot. Environmental predictors (rainfall, temperature seasonality, soil nutrient status, and topographic position) and biotic variables (phylogenetic diversity and species richness) were measured. Variation partitioning, fourth-corner analysis, and RLQ analysis were employed to decompose trait variance attributable to environment, biotic, and spatial components. Results showed that environmental filtering (soil phosphorus, aridity) explained 38% of community mean trait variation, while competitive displacement explained 21% of functional diversity variation. Stochastic assembly explained 41% of residual variation. An original Wet-Dry Niche Spectrum model is proposed to capture the trait-environment relationship along the rainfall gradient. These findings make an original empirical contribution to the ongoing debate on functional diversity assembly mechanisms in West African tropical forests.

Keywords: functional traits, tropical rainforest, community assembly, environmental filtering, West African forest