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.