Natural regeneration status and soil seed bank composition in IITA Forest Reserve, Ibadan, Oyo State, Nigeria

Abstract

The International Institute of Tropical Agriculture (IITA) Forest Reserve is a secondary rainforest that has been protected since 1965. It serves as a refuge for many species that were once common but have declined, due to urbanisation and population pressure. The study was conducted to assess the natural regeneration status and soil seed bank composition of the Forest Reserve. Two transects of 500 m were laid out using systematic line transect sampling technique. Ten sample plots of 25 m × 25 m (625 m2) on each line transect were used to identify tree species. Subplots of 5 m × 5 m for shrub and climber species, as well as 1 m × 1 m for herb species were demarcated at the corners and centre of the main plots for identification. Quadrats (15 × 15 cm) were laid out at the corners of the plots and at the centre for soil collection at depths of 0–5 cm, 5–10 cm and 10–15 cm. The regeneration status of species was determined based on sample size of seedlings, saplings and mature trees. Floristic compositions in the Forest Reserve included 58 tree, 26 shrub, 19 climber and 6 herb species. The natural regeneration status of the Forest Reserve was good with high numbers of seedlings (465/ha; 37.05%) and saplings (431/ha; 34.34%) compared with mature trees (359/ha; 28.61%). The families observed to be most abundant in the regeneration were Malvaceae, Moraceae and Apocynaceae. A total of 21 species was recorded using the seedling emergence technique. There were 11 herbs, six climbers, one shrub and three tree species. Similarity between standing vegetation and seed bank was low (0.067). The study revealed a poor soil seed bank composition, suggesting that regeneration of woody species from the persistent seed bank would be hampered if the standing vegetation is degraded.