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Floral change

Under "Floral change" I pooled together the papers concerning longer time periods showing more fundamental changes in the vegetation. They describe changes in the forest and woodland of Southeast Africa during the Mid-Brunhes Event (MBE) changes in the mountaineous forest in equatorial Africa during the Mid-Pleistocene Transition (MPT), Pliocene and Miocene changes in West Africa and Namibia, and a floral turn-over in west South Africa during the Late Miocene.

Mid-Brunhes Event

Effects of atmospheric CO2 variability of the past 800 kyr on the biomes of southeast Africa

Dupont LM, Caley T, Castañeda I
Climate of the Past 15 (2019) 1083–1097
doi:10.5194/cp-15-1083-2019

MD96-2048 summary
Summary of results of MD96-2048 showing the relative contribution of the endmembers E-Heathland, E-Mountain-Forest, E-Shrubland, E-Woodland, and the relative pollen abundances of vegetation groups, both as cumulative diagrams. On top the atmospheric CO2 curve of the EPICA Dome C ice cores. Note ages run from left (old) to right (young).

The Mid-Brunhes Event divides the Brunhes Chron (last 780 ka) into two periods in which the atmospheric CO2 maxima during the earlier interglacials (marine isotope stages 19, 17, 15 and 13) were lower than those during the later ones (marine isotope stages 11, 9, 7, 5 and 1). The pollen record of MD96-2048 (26°10’S 34°1’E, -660 m) off the Limpopo spans the complete Brunhes Chron plus two older Pleistocene windows. Endmember analysis resulted in four assemblages, E-Heathland, E-Mountain-Forest, E-Shrubland and E-Woodland. E-Heathland is characterized by Cyperaceae (edges) and Ericaceae (heather), but also by pollen from fynbos-like vegetation. Podocarpaceae (yellow wood) pollen dominates the E-Mountain-Forest assemblage. E-Shrubland includes pollen from coastal or halophytic settings together with arboreal and shrub taxa. E-Woodland combines pollen from Miombo woodland, other woody elements and mangroves. The endmember analysis indicates a very stable open ericaceous vegetation with partially wet elements such as sedges and Restionaceae characterizing the landscape of full glacials - when global temperatures and pCO2 were lowest. During the less extreme parts of the glacials, mountain Podocarpus forest was extensive as in most mountains of Africa. On the other hand, coastal shrubs were more abundant during interglacials. In the course of the Brunhes, the woody component, which was relatively weak before the Mid-Brunhes Event, became more and more important. It is likely that the Miombo dry forest and woodland migrated into the region in the successive interglacials of the Brunhes Chron. Particularly during Interglacials 9e and 1, the area might have been more forested than during the older interglacials of the Brunhes Chron.

Mid-Pleistocene Transition

Mid-Pleistocene environmental change in tropical Africa began as early as 1.05 Ma

Dupont LM, Donner B, Schneider RR, Wefer G
Geology 29 (2001) 195-198
doi:10.1130/0091-7613(2001)0292.0.CO;2

Over the Mid-Pleistocene Transition (ca. 1.2-0.8 Ma), the vegetation changed strongly in equatorial Africa as indicated by the decreased representation of tropical lowland forest and the increased representation of mountainous Podocarpaceae during glacial stages. Data are shown of ODP Site 1075 (4°79'S 10°8'E, -2996m). The temporally better resolved record for the last climate cycle of the nearby core GeoB1008 (Jahns 1996, Vegetation Hisory and Archaeobotany 5, 207-213) is denoted in grey shading.

 

Selected pollen of ODP Site 1075 offshore Congo
Summary of the palynological record of ODP Site 1075 (coloured shadings). Bottom up. Pollen percentages of Rhizophora (mangroves), tropical forest, Podocarpaceae (yellow wood from the mountain forest), fern spores and grasses. NB: time scale runs from left (old) to right (young) .

Pliocene

Late Pliocene vegetation and climate in Namibia (southern Africa) derived from palynology of ODP Site 1082

Lydie Dupont
Geochemistry, Geophysics, Geosystems 7 (2006) Q05007
doi:10.1029/2005GC001208

see also 'Miocene-Pliocene records > Namibia'

Development of vegetation and continental aridity in northwestern Africa during the Late Pliocene: the pollen record of ODP Site 658

Leroy SAG, Dupont LM
Palaeogeography, Palaeoclimatology, Palaeoecology 109 (1994) 295-316
doi:10.1016/0031-0182(94)90181-3

 

Periods of vegetation change in western Africa.

 

Comparing Pliocene pollen data from ODP Sites 658 (ca 20°N) and 1082 (ca 20°S)
A. global stack of stable oxygen isotopes of benthic foraminifers (Lisiecki & Raymo 2005). B & C. relative abundance of pollen of Rhizophora (B) and Amaranthaceae (C) in marine sediments of ODP Site 658 (21°N 18°W) after Leroy & Dupont (1994). D. relative abundance of Asteraceae pollen in marine sediments of ODP Site 1082 (21°S 12°E) after Dupont (2005). NB: time scale runs from left (old) to right (young)

Miocene

Miocene–Pliocene vegetation change in south-western Africa (ODP Site 1081, offshore Namibia)

Hoetzel S, Dupont LM, Wefer G
Palaeogeography, Palaeoclinatology, Palaeoecology 423 (2015) 102-108
doi:10.1016/j.palaeo.2015.02.002

The pollen record of ODP Site 1081 off northern Namibia (19°37'S 11°19'E, -794m) can be summarised into the three endmembers indicating floral changes. We used an Endmember model with three principal components or endmembers named after the stage/epoch in which they are dominant: TOR = Tortonian (9–7.5 Ma), MES = Messinian (7.5–5.3 Ma), PLIO = Pliocene (5.3-2.6 Ma). Although the majority of pollen does not score on one endmember only, the three endmembers differ clearly in their mixtures of pollen and spore types, which can be interpreted in terms of vegetation.

 

Vegetation Change ODP SIte 1081
Figure 3 of Hoetzel et al. (2015). Overview showing the relative contribution of the endmembers TOR, MES, PLIO, and the relative pollen abundances of vegetation groups, both as cumulative diagrams, and the pollen and spore concentration (logarithmic scale) of ODP Site 1081 (9–2.6 Ma). NB: time scale runs from left (old) to right (young).

 

Climate-driven rampant speciation of the Cape flora

Dupont LM, Linder HP, Rommerskirchen F, Schefuß E
Journal of Biogeography 38 (2011) 1059-1068
doi:10.1111/j.1365-2699.2011.02476.x

Tropical elements such as Petalidium and Balanites decline and disappear from this record retrieved west of the Orange River mouth during the Late Miocene, while drought resistence elements related to the winter rainfall zone such as Aizoaceae and Stoebe/Elytropappus appear. The uppermost samples are from the last glacial period and represent the recent flora of the Western Cape.

 

Selected pollen percentage curves from Miocene sediments of ODP Site 1085 (eastern South Atlantic offshore South Africa)
Selected pollen percentage curves of ODP Site 1085. CCA = Caryophyllaceae and Amaranthaceae.