Abstract
In Nigeria, most especially in the southwestern region, Tithonia diversifolia (Hemsly) A. Gray had been identified to be invasive following their introduction and fast spread, displacing the native species and affecting the soil nutrient status. Hence, we decided to evaluate the impact of T. diversifolia on the diversity and floristic compositions of native species and soil nutrient status of the invaded vegetation. Sample plots, 5 x 5 m each were established on invaded and uninvaded area in 10 sites in area invaded by T. diversifolia. In each plot, plant species enumeration was done to the species level and species diversity, evenness and index of similarity were evaluated. Soil samples were randomly collected at depth 0-15 cm and analyzed for chemical properties (pH, organic carbon, exchangeable cations (Ca, Mg, K and Na), nitrogen and phosphorus). One way ANOVA was used to determine significant difference in soil properties on invaded and uninvaded plots. The result showed that as compared to the control, in the Tithonia invaded area, the average number of plant species reduced by 25.4%; the Shannon-Wiener diversity reduced by 27% while the evenness reduced by 24.9% and the Sorensen index of similarity between the invaded and uninvaded plots for Tithonia was 32.6%. The invaded plots had higher pH, organic carbon, N, P and exchangeable cations than the uninvaded plot (p=0.05). We concluded that invasion of T. diversifolia is drastically affecting the diversity of the invaded areas and had significantly improved the soil fertility of the invaded sites. Key words: Invasive species, biological diversity, Shannon-Winner.
Highlights
The biota of the world is being homogenized as a result of the decline of native species and their replacement by a relatively small number of alien species that either deliberately or accidentally moves beyond their natural ranges (McKinney and Lockwood, 1999)
The plant samples collected from both invaded and uninvaded plots were analysed for nitrogen, phos-phorus, potassium, calcium, magnesium and sulphur according to the method of International Institute of Tropical Agriculture (IITA)
There were 34 families observed in T. diversifolia invaded and uninvaded sites with Fabaceae having the highest number (9) of species
Summary
The biota of the world is being homogenized as a result of the decline of native species and their replacement by a relatively small number of alien species that either deliberately or accidentally moves beyond their natural ranges (McKinney and Lockwood, 1999). Gray (Asteraceae), commonly called Mexican sunflower, is a common shrub (weed) native to Central America but has become naturalized in many tropical countries, including Nigeria. Kenya (Jama et al, 2000), Malawi (Ganunga et al., 1998), Nigeria (Ayeni et al, 1997), Rwanda (Drechsel and Reck, 1998) and Zimbabwe (Jiri and Waddington, 1998) It has been found in Cameroon, Uganda and Zambia (Shokalu, 1997). In Nigeria, most especially in the southwestern region, T. diversifolia had been identified to be invasive following its introduction and is fast spreading, displacing the native species and affecting the soil nutrient status. This study investigated the impact of T. diversifolia on the soil, species diversity and composition of vegetation
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