Developing an Original Multi-Trophic Framework for Assessing the Consequences of Plant Invasions on Ecosystem Function in Nigerian Protected Areas

Invasive plant species alter ecosystem function not only through direct effects on plant community composition but through cascading multi-trophic interactions affecting decomposer communities, herbivore networks, and pollinator assemblages, yet no multi-trophic framework has been developed or empirically tested for plant invasion consequences in Nigerian protected areas. This study develops an original multi-trophic ecosystem function assessment framework for plant invasion impacts and empirically tests it at invasion fronts of Chromolaena odorata, Mimosa invisa, and Tithonia diversifolia in four Nigerian protected areas: Okomu National Park, Old Oyo National Park, Kamuku National Park, and Yankari Game Reserve. The theoretical framework integrates invasion ecology theory, food web theory, and ecosystem function theory to generate predictions about how invasive plant dominance alters energy flow and nutrient cycling across trophic levels. At each invasion front, invaded and uninvaded paired plots were established. Plant community composition, above-ground and below-ground biomass, arthropod community composition (sweep net sampling), pollinator network structure (systematic pollinator observation), decomposer community (pitfall trapping, bait lamina assays), and ecosystem function metrics (litter decomposition rate, soil respiration, above-ground net primary productivity) were measured. Structural equation modelling was used to test multi-trophic pathway predictions. Results confirmed that invasive plant dominance reduced pollinator species richness by 41% and detritivore functional diversity by 36% in invaded plots. Litter decomposition rates declined by 28% in Chromolaena-dominated plots, attributed to high lignin content of its litter. The multi-trophic framework correctly predicted 76% of observed directional effects across trophic levels, demonstrating its empirical validity. The study makes an original contribution to invasion ecology theory by quantifying multi-trophic pathways of ecosystem function disruption in Nigerian protected areas.

Keywords: plant invasion, multi-trophic framework, ecosystem function, Chromolaena odorata, Nigerian protected areas