Tree Diversity, Functional Traits, and Ecosystem Multifunctionality Along a Forest Disturbance Gradient in Cross River State

The relationships between biodiversity, functional traits, and ecosystem multifunctionality have been extensively theorised in temperate and tropical systems, but their empirical validation along disturbance gradients in West African rainforest contexts is limited, creating a critical gap in understanding how forest management intensity affects the simultaneous delivery of multiple ecosystem functions. This study investigates relationships among tree species diversity, functional trait composition, and ecosystem multifunctionality along a forest disturbance gradient from intact lowland rainforest to logged forest and secondary vegetation in Cross River State. Fifty sampling plots were established across five disturbance categories, with tree diversity characterised through species richness, Simpson diversity, and phylogenetic diversity metrics. Seven key functional traits (wood density, leaf nitrogen, specific leaf area, maximum tree height, seed mass, rooting depth, and hydraulic conductance) were measured from 280 tree individuals representing 92 species. Six ecosystem functions were simultaneously measured in each plot: above-ground carbon storage, litter decomposition rate, nitrogen mineralisation, fine root biomass, tree water use efficiency, and seedling recruitment. Multifunctionality indices were constructed following the averaging approach and threshold method. Results demonstrate strong positive relationships between functional diversity and ecosystem multifunctionality, with species richness showing weaker direct effects after controlling for functional composition. Wood density and specific leaf area emerged as the most important trait axes driving multifunctionality responses to disturbance. Below minimum disturbance thresholds, multifunctionality showed surprising resistance, consistent with functional redundancy in intact rainforest. The study provides an empirical basis for functional-trait-based forest management guidelines for Cross River State. Keywords: functional traits, ecosystem multifunctionality, biodiversity, disturbance gradient, Cross River State