Pollen, biomes, forest successions and climate at Lake Barombi Mbo (Cameroon) during the last ca. 33 000 cal yr BP – a numerical approach
1ISE-M, UMR 5554 CNRS/Université Montpellier II, Place Eugène Bataillon, cc61, 34095 Montpellier cedex 5, France
2CEREGE, UMR 6635 CNRS/Université Aix-Marseille/IRD/CdF, BP 80, 13545 Aix-en-Provence cedex 04, France
3Université de Sciences et Techniques de Masuku, Département de Biologie, BP 913, Franceville, Gabon, France
Abstract. The aim of this paper is to provide a more complete and precise interpretation of the 33 000 cal yr BP pollen sequence from Lake Barombi Mbo, southwestern Cameroon (4°39'45.75'' N, 9°23'51.63'' E, 303 m a.s.l.), based on a numerical approach allowing quantitative estimates of vegetation and climate. The biomisation method was applied on fossil pollen assemblages to reconstruct potential biomes and forest successional stages. The modern analogues (MAT) and the artificial neural networks (ANN) techniques were used to reconstruct mean annual rainfall (Pann), mean annual potential evapotranspiration (PETann) and a bioclimatic index α related to the vegetation stature. Our reconstructions testifies of a dense forested environment around Lake Barombi Mbo of mixed evergreen/semi-deciduous type during the most humid phases (highest rainfall and lowest evapotranspiration reconstructed values), but with a more pronounced semi-deciduous facies from ca. 6500 cal yr BP to present day related to increased seasonality. These forests display a mature character until ca. 2800 cal yr BP then become of secondary type during the last millennium probably linked to increased human interferences. Two episodes of fragmentation are evidenced synchronous with the lowest rainfall and highest potential evapotranspiration reconstructed values, the first one centered during the LGM, and the second one from ca. 3000 to ca. 1200 cal yr BP linked mainly to high seasonality. But, as shown by low scores of savanna potential biome and successional stage, open formations never largely extend in the Barombi Mbo basin, and were more probably enclosed inside the forest in form of savanna patches. Concerning the climatic reconstructions at Lake Barombi Mbo, The ANN appears to be the most reliable technique in spite of under-estimated values of Pann all along the sequence mainly due to a lack of modern pollen data from very humid areas in central Africa.