Western equatorial African forest-savanna mosaics: a legacy of late Holocene climatic change?

Abstract

Abstract. Past vegetation and climate changes reconstructed using two pollen records from Lakes Maridor and Nguène, located in the coastal savannas and inland rainforest of Gabon, respectively, provide new insights into the environmental history of western equatorial African rainforests during the last 4500 cal yr BP. These pollen records indicate that the coastal savannas of western equatorial Africa did not exist during the mid-Holocene and instead the region was covered by evergreen rainforests. From ca. 4000 cal yr BP a progressive decline of inland evergreen rainforest, accompanied by the expansion of semi-deciduous rainforest, occurred synchronously with grassland colonisation in the coastal region of Gabon. The contraction of moist evergreen rainforest and the establishment of coastal savannas in Gabon suggest decreasing humidity from ca. 4000 cal yr BP. The marked reduction in evergreen rainforest and subsequent savanna expansion was followed from 2700 cal yr BP by the colonization of secondary forests dominated by the palm, Elaeis guineensis, and the shrub, Alchornea cordifolia (Euphorbiaceae). A return to wetter climatic conditions from about 1400 cal yr BP led to the renewed spread of evergreen Correspondence to: A. Ngomanda (ngomanda@yahoo.fr) rainforest inland, whereas a forest-savanna mosaic still persists in the coastal region. There is no evidence to suggest that the major environmental changes observed were driven by human impact.

Comparison of Small- and Large-Footprint Lidar Characterization of Tropical Forest Aboveground Structure and Biomass: A Case Study From Central Gabon

“…LNP is located in the western Lower Congolian semievergreen forests of central Africa [32] and is made up of dynamic, diversified vegetation types. Forest boundaries have been advancing, invading savanna grasslands under the influence of post-Pleistocene climate [32]- [34], yet anthropogenic uses of fire [35], together with the presence of elephant seed dispersal and browsing [36] have been modifying and maintaining the Lopé forest edge configuration and creating a complex system of forest types across this forest-savanna mosaic.…”

Comment on “Intensifying Weathering and Land Use in Iron Age Central Africa”

“…The second, caused by increasing seasonality of rainfall between 2500 and 2100 yr B.P., also was noticeable in the interior. The appearance of a marked dry season due to an abnormal southward shift of the intertropical convergence zone is corroborated by Saharan diatoms in dust deposited as far south as 4°N and the savanna crop Pennisetum glaucum in contemporaneous archaeological sites ( 4 , 5 ). Although at the periphery savannas were spreading, the rainforest crisis of the third millennium B.P.…”

“…state, but may have been collected from natural stands, as is done today. Pollen data clearly show that expansion of this pioneer species always followed climatically induced openings of the rainforest ( 4 , 12 ). Linguistic, archaeological, and archaeobotanical data are consistent with the hypothesis that the settlers took advantage of the secondary forest plant communities, which can be easily cleared and contain numerous useful tree species.…”

“…argue. In southern Cameroon, Gabon and the inner Congo Basin, a mosaic of mature and secondary forests with light-demanding trees developed ( 4 , 6 ). None of the palynological archives indicated in figure 1 of Bayon et al .…”

Palaeo-trajectories of forest savannization in the southern Congo

“…Climatically, drying has been associated with forest disturbance and contraction. Most notably, around 4000 BP, the end of the African Humid Period resulted in a decrease in rainfall [16] and savannization of sites along the forest margin [17,18]. Later, during the 'third millennium crisis' (approx.…”