Eméline P.S. ASSEDE (2014). Ecology of plant communities in the Biosphere Reserve of Pendjari, BENIN (West Africa). University of Abomey-Calavi, Bénin. 364 p.
Supervisor : Prof Brice Sinsin.
Abstract: My PhD study provided information and knowledge on the plant communities, plant ecology and population structure of the Biosphere Reserve of Pendjari (BRP). An overview of the flora of the BRP showed that plant species composition of 802 plant species distributed among 428 genera and 102 families, was typical of Sudanian savanna. The recorded endemic species of Benin demonstrated the importance of the reserve for plant conservation.
Two major floristic groups correlated with the gradient of soil moisture (drylands versus wetlands). Clear differences were shown between wetland plant communities while there were similarities between some dryland plant communities. Soil was one of the determining factors of the distribution of plant associations, and soil moisture was one of the main ecological parameters determining the establishment of species and plant association development. Ferruginous soils, poor in organic matter, are dominated on plateau with clay soils. In wetlands, the soils were a deep silty-clay without gravel.
The analysis of regeneration potential of different vegetation types identified in the BRP reflected the overall structure of the tree layer. Fire as main management tool of the BRP and seed viability explained the dominance of Fabaceae (28.8%) in the regeneration. However topography was a key element in plant establishment. Contrary to the floodplains where soils are poorly drained and poorly aerated, preventing good root penetration, plant regeneration was more important on the border of streams and the hill slopes.
The complexity of the regeneration strategy of plant species and factors controlling that, can also be read through the population structure, as the recruitment of seedlings determines the composition of future populations. A comparative analysis of the population structure of Pseudocedrela kotschyi and Terminalia macroptera in pure and mixed stands indicated that young T. macroptera individuals were predominant in both pure and mixed stands. Trees showed weak density and a random pattern. P. kotschyi young individuals were found to be predominant irrespective of standregime. Trees had a higher density and stronger clumped pattern in pure stands as compared to mixed stands.
The diversity and functional attributes of plants were changed but also recovered after disturbance.The secondary succession in the BRP exhibited a clear floristic pattern with a progressive establishment of the woody vegetation. The first state exhibited the highest species richness with 18.6% of all species exclusive to this state and was characterised by the proliferation of widespread species that disappeared by the third state. About 22% of the 233 species recorded were recorded throughout the fallow cycle. The transition from the first to the second state was characterised by the disappearance of 77% of the total species richness. Maintenance of a certain state of disturbance is important to maintain total plant diversity in the reserve. Organic matter and the species richness were the best discriminating variables of the succession states. The colonisation of the herb layer by Andropogon gayanus var. bisquamulatus(typical Sudanian species) in the third state can be seen as an indication of a substantial return of soil fertility.
Keys words : Ecology, Vegetation structure, soil properties, Pendjari reserve, Benin