Soil seed bank studies of Tithonia rotundifolia invaded fallow land and competitive association with Chromolaena odorata

Abstract

In Nigeria, Chromolaena odorata (L.) R. M. King and H. Rob and Tithonia rotundifolia (Mill.) S. F. Blake, are exotic invasive weeds, but a gradual decrease in the population of C. odorata with the rapid invasion of T. rotundifolia is now observed. Therefore, this study investigated the adaptive features of each weed in competition, with a further determination of seedling recruitment from the soil seed bank of plots invaded by T. rotundifolia. Field sampling was carried out in 10 plots: T. rotundifolia invaded plots and low or uninvaded plots in co-existing with other plants using 10 m x 10 m quadrats. The readily germinable seed species composition and the Sorensen index of similarity between the seed bank and their above ground vegetation were determined. Competition Series Experiment was also conducted for the two plants. Mariscus alternifolius (227) and Oldenlandia corymbosa (358) were the most abundant species in the seed bank while T. rotundifolia recruited 25 individuals. Low similarity index existed between the seed bank and the standing vegetation of the invaded and uninvaded plots. T. rotundifolia had improved growth in heteroculture with C. odorata over when in monoculture. However, a reduction in growth of C. odorata occurred when in competitive association with T. rotundifolia compared to when in monoculture. T. rotundifolia had competitive advantage over C. odorata.