Pollen, vegetation change and climate at Lake Barombi Mbo (Cameroon) during the last ca. 33 000 cal yr BP: a numerical approach

Abstract

Abstract. This paper presents quantitative reconstructions of vegetation and climate along the pollen sequence of Lake Barombi Mbo, southwestern Cameroon (4 • 39 45.75 N, 9 • 23 51.63 E, 303 m a.s.l.) during the last 33 000 cal yr BP, improving previous empirical interpretations. The biomisation method was applied to reconstruct potential biomes and forest successional stages. Mean annual precipitation, mean annual potential evapotranspiration and an index of moisture availability were reconstructed using modern analogues and an artificial neural network technique. The results show a dense forested environment around Lake Barombi Mbo of mixed evergreen/semi-deciduous type during the most humid phases (highest precipitation and lowest evapotranspiration), but with a more pronounced semi-deciduous type from ca. 6500 cal yr BP to the present day, related to increased seasonality. This forest displays a mature character until ca. 2800 cal yr BP, then becomes of secondary type during the last millennium, probably due to increased human activity. Two episodes of forest fragmentation are shown, which are synchronous with the lowest reconstructed precipitation and highest potential evapotranspiration values. The first of these occurs during the LGM, and the second one from ca. 3000 to ca. 1200 cal yr BP, mainly linked to high precipitation seasonality. Savanna were, however, never extensive within the Barombi Mbo basin, existing instead inside the forest in form of savanna patches. The climate reconstructions at Lake Barombi Mbo suggest that the artificial neural networks technique would be more reliable in this region, although the annual precipitation values are likely under-estimated through the whole sequence.

Towards an understanding of West African montane forest response to climate change

“…The transition from arid (glacial) to humid (Holocene) climate occurred between 18.5 and 15.5 cal. kyr bp in west‐central Africa, as recorded by the rise of lake level at Lake Bosumtwi (Shanahan et al ., ), the increase of fluvial activity in the Gulf of Guinea (Lézine et al ., ; Weldeab et al ., ; Kim et al ., ; Sangen et al ., ) and forest expansion in the equatorial lowlands (Maley & Brenac, ; Lebamba et al ., ). This timing matches the Bambili record, which shows that the local forest was extremely reduced during the terminal last glacial period, and started to expand in two steps dated at 18.4 and 15.5 cal.…”

Tree Age Distributions Reveal Large-Scale Disturbance-Recovery Cycles in Three Tropical Forests

“…For example, landscape-scale fires of low intensity (Baker and Bunyavejchewin, 2009) or region-wide tree mortality following extreme drought events (Nepstad et al, 2007; Allen et al, 2010) are both extensive disturbances with highly heterogeneous patterns of tree mortality and subsequent recruitment. A few studies have demonstrated the occurrence of severe and broad disturbances in tropical forests on a millennial time scale, through genetic analyses and pollen research (e.g., Daïnou et al, 2010; Lebamba et al, 2012). Forest monitoring studies on the other hand are unlikely to capture the dynamics caused by infrequent severe and/or large-scale disturbances because they are generally conducted in small permanent plots for several decades (e.g., Baker et al, 2004; Clark et al, 2010).…”

Patterns of land-use change and current vegetation status in peri-urban forest reserves: the case of the Barombi Mbo Forest Reserve, Cameroon

“…Lake Barombi Mbo is located at latitude 4°39ʹ45.75" N, and longitude 9°23ʹ51.63" E, in Kumba, South West Region of Cameroon (Lebamba, Vincens, & Maley, 2012) at an elevation of 301 m asl and is about 60 km NNE of the 4100 m high active Mt. Cameroon strato volcano (Fonge, 2004).…”