Tolulope Victor Borisade’s research while affiliated with Bamidele Olumilua University of Education, Science, and Technology, Ikere-Ekiti and other places

The introduction of invasive species is known to cause changes in the structure and composition of native communities. These changes are not only restricted to the aboveground vegetation, but may be equally expressed in corresponding soil seed banks, which are legacy effects of the vegetation. This study assessed the impact of the invasive plant, Alternanthera brasiliana, on the vegetation community and its soil seed bank in Ile-Ife, Nigeria. Sample plots were established in invaded plant communities, with high density of Alternanthera brasiliana, and uninvaded plant communities with low density or no presence of Alternanthera brasiliana. Subplots were placed in each large sample plot and in each subplot all rooted plant species were identified and counted. Samples from the post-dispersal soil seed bank were collected to estimate the soil seed bank density and floristics. The species composition of soil seed bank was compared with that of the above-ground vegetation to assess the invader’s impact on the vegetation and soil seed bank. The results showed that the presence of Alternanthera brasiliana significantly impacted on the species diversity (t = 5.27; df = 18; p = 0.0003) and species evenness (t = 4.50; df = 18; p = 0.00005) in the aboveground vegetation, and the species diversity (t = 5.37; df = 18; p = 0.00004) and species evenness (t = 6.19; df = 18; p < 0.0001) in the soil seed bank. This study showed that Alternanthera brasiliana has caused ecological alterations in the aboveground vegetation as well as in the soil seed bank. It is likely that with increasing resident time, the impacts on native species will increase as Alternanthera brasiliana spreads.

Interplay between soil variables with structural and diversity indices of riparian vegetation needs to be explicated towards the conservation of this highly productive riparian forest ecosystems amidst pronounced anthropogenic activities in Southwestern Nigeria. The study was carried out in Osun State, Southwestern Nigeria. Nine sites were used for this study, within each site, ten plots (0.25 ha in size) were marked out and each plot was placed systematically, giving a total of 90 plots. Ten soil samples were collected in each plot at top (0-15 cm) and sub (15-30 cm) soil levels using soil auger and to analysed for the physicochemical properties. Woody species were identified and classified. Euphorbiaceae and Apocynaceae are the most occurring families with Musanga cecropioides, Pterocarpus santalinoides, Rothmannia hispida and Jateorhiza macrantha being dominant in the riparian sites. The soil variables correlated positively with structural parameters markedly density rather than diversity indices across study sites. Soil pH, P, TOC, OM were key edaphic factors that affected the vegetation dynamics of these ecosystems. Policies and decision making should take cognisance of these key nutrients supporting dominant species, towards conservation amidst ecological succession ongoing across the riparian forest sites.