Survey of Invasive Species among the Weed Flora in Selected Tree Crop and Forest Tree Plantations in Ibadan, Nigeria

Plant invasions are a worldwide occurrence that have detrimental impacts on the environment. Monitoring the status of invasive species in tree crops and forest plantations is essential for informed management decisions. This study identified weed species in selected tree crop and forest tree plantations in Ibadan to evaluate the prevalence of invasive weed species within the plant community. A systematic sampling design was employed for the enumeration of weed species in the plantations (Oil palm and Teak plantations in the University of Ibadan, and Mango and Organic Citrus Orchards in the National Horticultural Research Institute, Ibadan). Weed species rooting within 56, 58, 48 and 60 quadrats (1 m x 1 m) in oil palm, teak; mango and citrus respectively were identified and enumerated. The density and frequency of the weed species were calculated following standard procedure and Relative Importance Values (RIV), Shannon-Wiener, Dominance and Jaccard’s Similarity indices were further determined. Invasive species like Alternanthera brasilliana (6.96% RIV in Oil palm), Chromolaena odorata (9.95% in Teak), Andropogon tectorum (7.58% in Mango) and Tithonia diversifolia (7.56% in Organic Citrus) were present in the plantations. The Shannon-Wiener index was relatively high and ranged from 2.81 to 3.21 while the dominance index was low and ranged from 0.05 to 0.09 in the plantations. The Oil palm plantation and Organic orchard were most similar (73.68%) while Oil palm and Teak plantations were least similar (20.76%) based on weed species. Invasive species were present in the plantations, and this may lead to suppression of indigenous species.