Assédé Eméline Sessi P., Kouton Meryas, Brice Sinsin:
Vegetation and Soil Dynamics in the Fallows Around the Biosphere Reserve of Pendjari in Northern Benin (West Africa)

ASSÉDÉ EMÉLINE SESSI P., KOUTON MERYAS, BRICE SINSIN
University Abomey-Calavi, Laboratory of Applied Ecology, Benin

Always considered as the hotspot of biodiversity in Benin, the Biosphere Reserve of Pendjari has been safe from human pressures for long time. The demographic increase is constraining more and more the reserve in terms of land need for agriculture. This work aims to study the vegetation of the fallows around the Reserve, to determine the ecological characteristic parameters of the different stage of the fallows, then to deduct the ecological optimum of fallow duration. 132 phytosociological measurements have been made with the Brawn Blanquet method inside sample areas of 900m ² in different age of fallows. Appropriated soil sample analysis permitted to study the ecology of the different succession phases. The measurements have been ordinate by non metric scaling method with the statistical software R. For soil data, first order position parameters have been calculated with Microsoft Excel. The cycle of the secondary succession varies between 10 and 15 years. The passage from a stage to another is characterised by the appearance of new species, the disappearance of others related to the soil parameters. The rate of species appeared and extinct decreases with the age of the fallow. From the 242 plant species counted for this survey, 22.3% are present along the cycle. More than 70% of the species disappear after the first three years of the succession. This stage is 90% constituted by yearly species as Digitaria horizontalis, Indigofera pulchra. The phases evolved of the succession (7 to 10 years) are characterised by the appearance of perennials (Andropogon gayanus) and woody (Combretum micrantum, Terminalia avicennioides) species. With 24% of total species richness only 4% are exclusive to this stage. The species achieve their maximum at the end of the cycle. The sandy soil in the beginning of the succession with a very low rate of organic matter (2.42%) is poor in exchangeable bases (Mg²⁺ = 1.34 %; Ca²⁺ = 2.10%). At the end of the succession, soil is sandy clay with the most elevated rate of organic matter (4.69%). The ecological optimum is gotten after 8 years of fallow.

Keywords: Biodiversity, fallow, Pendjari reserve, secondary succession, vegetation

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Contact Address: Assédé Eméline Sessi P., University Abomey-Calavi, Laboratory of Applied Ecology03 Bp 1974, Cotonou, Benin, e-mail: emimissyahoo.fr