The forest land's conversion into tree crops plantations plays a major role in the loss of biodiversity. Therefore, understanding the impacts of land-use change on species diversity is very critical for ecosystem functioning and stability. This study was carried out to evaluate the effect of land-use changes on under storey species diversity in the Theobroma cacao and Citrus sinensis plantations. Two, 25 m × 25 m plots were sampled in each plantation and a nearby undisturbed secondary rainforest for comparison. The diameters (dbh-1.3 m) of all trees at breast height >10 cm were measured in each plot. Five line transect were systematically laid and a quadrat of 50 cm × 50 cm placed at every 1 m point to identify the under storey species (herbaceous, shrubs, tree saplings and climbers) present in each plot. Percentage canopy, species diversity using Shannon-Wiener, Simpson's index and Evenness were determined, while species similarity was determined using the Jaccard's similarity index. Results indicate that woody basal area and stem density in Theobroma cacao were significantly (P<0.05) higher than the Citrus sinensis plantation. A total number of 25, 27, and 14 under storey species distributed in 16, 19 and 11 families were found in Theobroma cacao, Citrus sinensis plantations and secondary forest respectively. Panicum maximum and Axonopus compressus were the dominant grasses in the Theobroma cacao and Citrus sinensis plantations respectively. The percentage canopy cover was significantly (P<0.05) higher in the secondary forest than the plantations. The land use modification has significantly increased the under storey species composition.

A soil survey of Onigambari forest reserve in Oyo State, Nigeria was carried out. Three soil mapping units Established-Teak-Plantation (ETP), Natural-Forest (NF) and Farm-Land (FL) were identified with observation base on vegetative pattern. Morphological properties of the study area show that the soil unit ETP is deep and texture ranges from loamy-sand at the surface to sandy clay loam in the subsurface. The soil unit NFand FL is not deep due to presence of hard pan but the texture ranges from sandy-loam to sandy-clay and loamy sand to sandy-clay respectively. Physical properties of the soils showed the bulk density of the soils to be moderately good for growing plant with high porosity. The soils chemical properties indicate that the pH value of the soils in ETP, NF and FL are slightly acidic and organic-matter was very low in the soils of ETP compared to NF and FL soils. The total-nitrogen values of the soils in the area changed irregularly with depth and values ranged from 0.028 to 0.1g kg-1 in ETP, 0.05 to 0.25g kg-1 in NF, the value ranged from 0.03 to 0.26 g kg-1 in FL. 0.03 to 0.26 g kg-1. According to USDA soil Taxonomy system, all the profiles pits in the study area showed distinguishing characteristics of the order Alfisols, therefore the soils are classified as Alfisols. Profile in the Established-Teak-Plantation is classified as Typic isohyperthermic paleustalfs, Profiles Natural-Forest and Farm-Land with petro-plinthic material within 100cm of the soil surface qualified as plinthic isohyperthermic paleustalfs.