Abstract
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.
Highlights
The lowland rainforest has been reported to be the most species-rich terrestrial ecosystem having more than 50-70% of all living organisms on approximately 6-7% of the land area (Linsenmair, 1990, 1997; Wilson, 1992)
This study examined the under storey plant species in Theobroma cacao, Citrus sinensis plantations and, compares the species diversity with that of a nearby rainforest with a view to provide information that will be vital to biodiversity functioning and conservation, following the conversion of forest to plantation ecosystems, and serves as a baseline data for future study
A total of number of 25 and under storey plant species distributed in and15 families were found in Theobroma cacao and Citrus sinensis respectively, while 14 different species were distributed in 12 families in the nearby secondary forest (Tab. 1)
Summary
The lowland rainforest has been reported to be the most species-rich terrestrial ecosystem having more than 50-70% of all living organisms on approximately 6-7% of the land area (Linsenmair, 1990, 1997; Wilson, 1992). The impacts that have been of primary concern are the effects of land-use change on biological diversity, soil degradation and the ability of biological systems to support human needs. Tree crop species plantation has become mostly planted in most countries due to the fact that it is fast-growing and because of the economic value (Lavery and Mead, 1998). Plantations of fast-growing exotic tree species have become increasingly important land use in the tropical regions with following tree crops species; Theobroma cacao, Cola nitida, Coffea arabica, Citrus sinensis, Elaeis guinensis, and fast-growing timber trees like Gmelina arborea, Tectona grandis plantations becoming more common in Nigeria because of their economic gain, and the need to control soil erosion and soil degradation. The availability of plantation forestry has been pointed out to reduce pressure on native forests (Ponce, 2000), which are rapidly being depleted
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