forest composition and analyse its response to changing environmental conditions. Henga-Botsikabobe et al. (2020) then later published detailed results from 23 tropical marshes within the Lope National Park examining modern pollen-vegetation relationships. Surface samples were collected from 50 random points across each marsh environment and homogenised to obtain one representative sample per marsh. They found that the modern pollen signal is highly influenced by the local marsh vegetation and a very high diversity of forest taxa are recorded, making it possible to quantify changes between adjacent mature, secondary and pioneer forests. Low proportions of Poaceae were found in the surface samples, which is thought to be influenced by their mode of deposition. This challenges common interpretations, which use these proportions as a measure of savannah vs. forest. This is a unique study from an alternative depositional context and provides unique insights for interpreting modern samples and core sequences from marsh environments.

### 21.4.5 Republic of the Congo

Modern palynological studies in the Republic of Congo are concentrated in the South and South West of the country, within the Batéké Plateau and Mayombe massif regions and along the littoral coast. Elenga et al. (1994) examine two cores from a swamp in the Batéké Plateaux region of the Congo, within the Guineo-Congolian region (White 1983) to illuminate palynological evidence of past vegetation change. While this study does not focus on modern pollen-vegetation relationships, it utilises insights and results from a previous doctoral study by Elenga (1992) incorporating modern pollen rain from the same region. For example, Elenga et al. (1994) comment on the large local pollen production of Gramineae.

Elenga et al. (2000) later carry out a more focused study on the pollen-vegetation relationships in the same region. Palynological data was analysed from 12 sites, each comprising 20-30 surface subsamples and compared to forest inventory data. At the local scale, the modern pollen rain largely reflected the forest taxa observed, and due to the dense canopy, only a few grains originated from extra-local sources. There were variations in the pollen production of individual species and Elenga et al. (2000) found that certain species, which are characteristic of these forests, are found in low percentages in the surface samples, for instance, species in the families Caesalpiniaceae, Euphorbiaceae and Annonaceae. Equally, a number of taxa may be overrepresented in the pollen spectra due to high pollen productivity (e.g. *Treculia, Syzygium* and *Dacryodes*).

Tovar et al. (2019) examined 12 surface samples and a core sequence from a monodominant *Gilbertiodendron dewevrei* (De Wild.) J. Léonard forest in the northern Republic of Congo. The authors found that *Gilbertiodendron* represented between 3.8% and 6% of the pollen count in the surface samples from the monodominant forest patches. The most abundant taxa in these samples were *Lophira alata*-type and *Celtis* spp. No *Gilbertiodendron* pollen was found in samples outside the monodominant patches. These studies provide important insights into the pollen production and dispersal of key Congo Basin taxa which are important for many palaeoecological interpretations in the region.

While currently, modern pollen-vegetation studies are relatively scarce across the Congo Basin, the recent discovery of a large area of peatland in the Cuvette Centrale (Dargie et al. 2017) has sparked new research in the region. The peatland represents an important palaeoecological archive, which may hold insights into additional pollen-vegetation relationships in this alternative depositional context.

### 21.4.6 Democratic Republic of the Congo

There are no modern pollen studies solely within the Democratic Republic of Congo. A single palaeoecological study exists from the Lake Edward Basin, which spans the Ugandan-Congo
border (Beuning and Russell 2004). This study examines a lacustrine core to reconstruct the climatic and vegetation history of the area, with reference to a number of modern pollen assemblages collected from crater lakes within Maramagambo forest reserve, on the Ugandan side of the border. While the authors found that the modern pollen assemblages contained taxa similar to those found in the basal metres of the Lake Edward Basin core, the percentages of Poaceae varied, indicating that the basal metres of the core were more similar to the pollen spectra of the semi-deciduous forest to the east of Lake Victoria, potentially representing a comparable modern environment.

## 21.5 EAST AFRICA

East Africa is where some of the continent's foundational modern pollen work was conducted (Coetzee 1967; Hedberg 1954; Livingstone 1967). An early review of modern pollen work conducted in the tropics included a summary of East African montane work (Flenley 1973). Several countries, however, do not appear to have any studies of modern pollen rain; Eritrea, Somalia and South Sudan. Laseski (1983) analysed 59 surface samples from Uganda, Rwanda, Tanzania, Zambia, Kenya and Tanzania. These samples were used to derive relationships between pollen and rainfall, and are included in analyses such as Gajewski et al. (2002) but the original thesis was not available for this review and is therefore not covered in detail here. Vincens (2006) analysed a large number (150) of modern pollen samples across seven phytogeographical regions. These are used in biomisation with a high level of success (82.6% of sites correctly assigned). These studies by Gajewski and Vincens demonstrate the usefulness and potential of accessible, broad-geographical and climatic analytical studies on modern pollen in the tropics.

### 21.5.1 Sudan

Eleven soil samples were analysed by Ghazali and Moore (1998) from an initial set of 30, the majority of which did not contain pollen. These were taken from desert, semi-desert, scrub and grassland ecosystems. Poaceae was, by far, the most abundant pollen type identified in the samples. Non-arboreal pollen dominated generally, which is a true reflection of the nature of the ecosystems sampled. A higher proportion of entomophilous pollen than might usually be expected was found in some samples, including *Acacia* pollen despite no *Acacia* trees being present within a 100 m radius of the sample site. Further work by Ghazali (2002) resulted in seven more samples (including one collected in a moving vehicle) from along a transect in the Nile Valley, encompassing mainly desert ecosystems. The assemblages from these samples were mostly dominated by anemophilous taxa such as Poaceae, although only 8 out of 40 pollen taxa identified were anemophilous. It was noted by the authors that, as in their previous study, a large number of samples of those originally collected did not contain pollen. This is likely due to the highly arid climate and sometimes alkaline soils of Sudan.

### 21.5.2 Djibouti

Three modern samples, from river sediment, lake surface mud, and soil, from desert sites in Djibouti are presented in Bonnefille et al. (1980). These samples are presented for comparison with the results from a core dated to 45,000 yr BP, although only three samples possessed high concentrations of pollen, likely due to arid climate conditions. The modern samples showed higher levels of Cyperaceae and forest taxa, but lower Poaceae than those from the core.
### 21.5.3 Ethiopia

Ethiopia has been the site of many studies of early hominin evolution, including some pollen work from site Fejej FJ-1 establishing palaeoecological histories for archaeological finds (Mohamed Umer et al. 2004).

Bonnefille et al. (1987) studied modern pollen samples from the Awash Basin from an elevational range of 500–3000 m asl and four vegetation types; subdesert steppe, riparian, evergreen bushland and montane forest. River and soil samples were taken and used to inform interpretations of the Hadar formation, from between 2.9–3.3 million years ago. These data are used to infer climate conditions during the evolution of early hominins. Another study from Bonnefille et al. (1993) found that modern pollen samples separated vegetation communities from different altitudes well, although due to high levels of entomophily, the taxonomic composition was not accurately reflected.

Recently, 20 modern pollen (and phytolith) samples from springs in Awash Valley have been published (Barboni et al. 2019) which allowed records from fossil springs to be interpreted. These spring environments are thought to be important environments for early hominins, as constant supplies of water in otherwise fluctuating or arid landscapes, therefore playing an important role in early hominin evolution and dispersal.

A large number of modern pollen samples from Ethiopia (with fewer samples from Kenya and Burundi) were included in studies that aimed to develop transfer functions to reconstruct rainfall (Bonnefille et al. 1992; Roeland et al. 1988) and temperature in fossil records. It was found that it is possible to reconstruct modern temperatures and precipitation with a high degree of accuracy based on the large and geographically widespread datasets used in the analyses.

### 21.5.4 Uganda

Hedberg (1954) sampled moss and lichen, predominantly from Carex bogs, within the Alpine and Ericaceous belts of the Ruwenzori Mountains in Uganda. It was found that, within the Alpine belt, pollen dispersal is predominantly local. Ericaceous pollen is found to be, although relatively local in its dispersal, a potentially useful indicator taxon. For other taxa, similar conclusions were drawn for these Ugandan samples as for those from Mount Kenya.

Osmaston (1958) conducted palaeoecological work in the same region as Hedberg (1954) and Livingstone (1967) took cores from Lakes Bujuku, Kitandra and Mahoma, whose top-most sediments can be considered surface samples. These core-top samples showed low levels of Poaceae, even in alpine belts, leading Livingstone dismiss Poaceae as an indicator of cooler alpine conditions in the past.

Hamilton (1972) analysed modern samples from Kigezi (largely samples from swamps) and Ruwenzori (various environments) and Mount Elgon (within the 'Montane Forest' and 'Ericaceous and Afroalpine' Belts). These samples demonstrated that, in general, transport of pollen to higher altitudes from low altitudes is more common than in the opposite direction. Flenley later hypothesised that this was due to wind directions generally being up slope in the day and downslope at night, and that pollen is generally released in the day (Flenley 1973). Hamilton used the modern samples to develop lists of pollen types by dispersal propensity, and from these lists made suggestions on the interpretation of pollen diagrams, including the fact that aquatic taxa and taxa that likely represent long distance transport are omitted from pollen sums.

Vincens et al. (1997) used modern data from previous studies, as well as including original data from surface samples from their own research and previously unpublished data to investigate pollen rain across a wide environmental and elevational gradient in Uganda. Their study encompassed multiple vegetation types including savannah, forest-savannah mosaic, montane forest, the Ericaceous belt and the alpine belt. They found that modern pollen rain can successfully
separate different vegetation types but that characteristic plant taxa of certain ecosystems may
be completely lacking from their pollen signals.

In their paper from Mubwindi Swamp, south-west Uganda, Marchant and Taylor (2000) present data of modern pollen spectra recovered from surface samples of sediment. Pollen types encountered were grouped into five categories, according to their level of representivity when compared with abundances of the same taxa in the sampled vegetation: under representative, moderately under representative, representative, moderately over representative, and over representative. The results of this research show that most of the dryland pollen incorporated into swamp sediments is produced by local plants close to the site of deposition. Generally, abundances of arboreal taxa such as *Alchornea*, *Anthocleista*, *Croton*, *Dombeya*, *Ilex*, *Myrtaceae*, *Newtonia*, *Polyscias*, *Prunus*, *Rapanea* and *Zanthoxylum* in the modern pollen appear to closely reflect the occurrence of their parent taxa within the surrounding vegetation. This close relationship between the representation of the parent taxa in dryland vegetation and the pollen percentage in surface samples allows the incorporation of these taxa in the nonlocal pollen sum (Marchant et al. 1997).

21.5.5 Kenya

Hedberg (1954) conducted the first modern pollen analyses for Kenya, using moss and lichen samples taken from the Teleki Valley, Mount Kenya. He also sampled ice from the peak of Mount Kenya for pollen, which was found to contain many pollen grains and spores, assumed to be from the preceding years to decades. *Podocarpus* was found to be abundant in the moss samples, demonstrating long-distance transport of 6-10 km. Samples from the Bamboo forest zone were found to contain little Poaceae pollen, which was attributed to Bamboo's irregular flowering and death after flowering. *Alchemilla* was found to be locally abundant, with poor dispersal. Hedberg also determined that it was not possible to determine *Senecio* forest from its pollen spectrum alone, as similar amounts of 'Compositae: Tubiflorae' (the Asteraceae pollen type used that included *Senecio*) were found in samples from other vegetation types. Undifferentiated *Lobelia* pollen was found but was not considered to be of any use as an indicator taxon due to the occurrence in the area of various species of *Lobelia* with different environmental preferences. Coetzee (1967) also examined modern pollen samples from Mount Kenya, and drew similar conclusions to Hedberg (1954) around the abundance of *Podocarpus*. Rucina (2000) also notes over-abundance of *Podocarpus* from modern samples from the Aberdare Mountains, south-west of Mount Kenya. Hamilton (1972) noted that the analyses of Coetzee and Herberg possessed relatively low taxonomic resolution. This issue was somewhat addressed by Livingstone (1967) who worked from a better reference collection and published results including core-top samples from Uganda (see Uganda).

Modern pollen on Mount Elgon (which experiences different weather patterns on its south-
ern and eastern flanks, with the southern receiving higher rainfall) was studied by Hamilton
and Perrott (1980) who used both soil samples and pollen traps along two elevational transects.
Of these transects, one was on the wetter southern side of the mountain, and the other was on
the drier, eastern side. Due to their transects being elevational, a number of different vegeta-
tion types were sampled; Montane forest, Ericaceae thicket, High altitude grassland, *Alchemilla*
scrub, Rocky ground communities, Mires, and agricultural land. Their findings indicated that
Montane forest produced the most pollen, and that it was represented in other areas both up
and downslope of its extent. Poaceae pollen abundances were found to reflect the local abun-
dance of grasses in the vegetation. Many pollen taxa, including *Schefflera* and Amaranthaceae,
were found to disperse very poorly and do not travel far from their parent plants, whereas some,
such as *Acalypha*, *Urticaceae*, *Juniperus*-type and *Podocarpus*-type, demonstrated long-distance
transport. Sediment samples taken nearly a decade apart (1967 and 1976) showed very similar
pollen assemblages, leading the authors to conclude that surface samples represent longer-term
modern pollen deposition well. Vincens (1984) investigated modern pollen from Lake Turkana and concluded that only 7% of pollen in the lake was aerially deposited.

A biome reconstruction using modern pollen data from East Africa used 40 sites from North-
ern Kenya (Vincens et al. 2006), the modern pollen rain was assigned into plant functional types
then biomes. The study indicated that modern pollen rain correctly predicted modern vegetation
types except in transition zones where the drier/more open vegetation type was predicted. This
Vincens (2006) study includes the results and data from previous unpublished studies by the same
author. A study running between 2014 and 2015 set up pollen traps in the Mau forest (around
Nyabuiyabuyi swamp) and the Amboseli Park at Kimana, Ormakau and Isinet swamps. 30 pollen
traps at each site (total 120) were left at each site for a period of 1 year (Githumbi 2017). During
the recovery of the traps a year later only at Nyabuiyabuyi were 21 of the 30 traps recovered, at the
other sites the recovery rate was less than 20%. The major cause of trap disappearance/selection
was wildlife. Due to this, new initiatives in Amboseli are in progress where new traps are to be
located in areas that can be continually monitored to ensure survival of the traps.

21.5.6 Burundi

Bonnefille and Riotlet (1988) conducted a study of modern pollen as part of work on a core from Kashiru Swamp, in the Burundi highlands. They collected soil samples from a range of different altitudes in the Teza forest, between 2100 and 2500 m asl. These samples were taken across the montane forest-Ericaceous moorland transition, and reflected this vegetational change. Ericaceous pollen did not disperse far from its vegetation zone, and as altitude increased, a sharp decrease in arboreal pollen was observed. *Macaranga* pollen accounts for around 40% of the pollen from the montane forest samples, and the authors interpret this as a sign that these forests may have been previously disturbed. They also note that the trees that are characteristic of the forest (*Entandrophragma*, *Prunus*, *Chrysophyllum and Neoboutonia*) are extremely rare in the modern pollen spectra.

21.5.7 Tanzania

Modern pollen work in Tanzania was conducted by Vincens (1987) on Lake Natron. It was established that modern pollen assemblages recovered from the lake were relatively uniform across the lake except from where rivers emptied into the lake. Pollen assemblages from the lake surface samples captured the important vegetation types in the catchment basin, but not in a representative manner.

From a modern pollen-rain study along the elevational gradient on Kilimanjaro Schüler *et al.* (2014) show that it is crucial to establish a modern pollen-rain-vegetation relationship for the calibration and interpretation of a fossil pollen record from mountain sites across a gradient of alpine vegetation types including savannah, lower montane, middle montane and upper montane forest types. On Kilimanjaro, the authors analysed modern pollen-rain on plant family level to derive the elevational forest zone (lower, mid, and upper forest zone as per Hemp (2006)) of the surrounding vegetation. Climatic conditions of the study sites were further assessed and put into relation with pollen-rain and forest vegetation (Schüler 2013) which is important for the interpretation of palaeo-records. However, it was shown that the occurrence of plant families along the altitudinal gradient are differently represented in the modern pollen depending on their various reproduction factors. This can further be quantified as a transfer factor as introduced for montane forest taxa in south west Uganda by Marchant and Taylor (2000). The diversity trend captured in the modern pollen-rain on the elevational gradient on Mt Kilimanjaro reflects the plant diversity in the vegetation. However, Schüler *et al.* (2014) observed differences in the taxa richness as the pollen and fern spore dispersal seems to be strongly influenced by the regional wind patterns.
Ivory and Russell (2016) collected modern pollen samples from Lake Tanganyika, which showed consistently high levels of Poaceae pollen (>60% in all samples) and low levels (<6%) of forest taxa even when intact forest was present on the shoreline very close to the sampling site. They conclude that modern pollen assemblages in Lake Tanganyika do reflect, to some extent, the shoreline vegetation, and that depth is not a significant factor in the assemblage composition.

### 21.5.8 Malawi

Modern pollen samples in Malawi were collected by Meadows (1984), who used a combination of pollen traps and soil samples on the Nyika Plateau. Pollen traps placed at ground level and one metre height were compared and found to produce extremely similar assemblages. The author found that pollen trap and surface samples produced very similar pollen spectra, even with the amount of re-worked pollen being similar. Re-worked, in this instance, implied re-floated into the atmosphere. The three vegetation types investigated in the study, Dambo (shallow wetlands), Grassland and Forest were able to be distinguished by their pollen spectra. Some pollen taxa were found to be 'well-dispersed', including Ericaceae (in contrast to other studies from East Africa eg. (Hamilton 1972)), Poaceae and Cyperaceae. Further samples were collected and analysed from surface samples of Lake Malawi itself by DeBusk (1995, 1997), who found that high levels of mixing, and different inputs (e.g. wind versus riverine) led to a very coarse signal within the lake, from which it was not possible to distinguish distinct pollen assemblages corresponding to vegetation types on the shores.

## 21.6 SOUTHERN AFRICA

Within the tropics of Southern Africa, a relatively large number of studies have been carried out in some countries, including in Madagascar and South Africa. Angola, Botswana, Mozambique and Zimbabwe lack any modern pollen studies in their tropical regions.

### 21.6.1 Madagascar

Modern pollen samples from Madagascar mostly covered the sub-humid forest grassland mosaic of Central Highlands with little to no representation of the dry deciduous forest, savannah woodland, and the spiny thickets in the south western region. Early surface sample analysis for palaeoecological purposes was conducted by Burney (1988) based on 13 perennial lakes and bogs in the sub-humid forest grassland mosaic of Central Highlands. These wetlands were sampled directly, by pushing a vial into the surface of the bog using various devices, depending on the water depth and type of sediment (Burney 1988). Based on the rate between arboreal pollen (AP) and non-arboreal pollen (NAP) distinction of taxa associated with grasslands (with grass pollen ≥55%), forest/grassland mosaic (grass pollen between 22–38%), and montane shrub grassland (Ericaceae pollen ≥40%) were identified. The presence of Ericaceae-dominated montane shrub grasslands and the forest formations of the northern and eastern parts of the island were recorded. Along these, ecosystems such as riparian woodlands on the lakeshores, patches of montane were also represented as the case of the sample collected at Ankazominady in the central highlands. These findings enabled interpretations of palaeoecological work and established at least a qualitative distinction between Malagasy paleoenvironments in the region. However, Burney suggested the need for larger modern pollen datasets and the inclusion of more phytogeographic information combined with multivariate statistical methods for better interpretations.

Straka (1991) published 89 samples from mosses and surface sediments within which 60 samples were from Madagascar. Straka's samples represented seven vegetation types. The humid forest included seven samples with three samples in the littoral forests, three in the
humid forest at low altitude, and one in the secondary forest called *Savoka*. However, most of the samples were collected in the subhumid forest in the Central Highlands with a total of 48 samples. The ericoid thickets were represented with four samples which were characterised by a high percentage of Ericaceae/Vaccinaceae (45–98%) with low diversity or with a moderate percentage of Ericaceae/Vaccinaceae combined with Asteraceae type Aster (30%). For all the samples analysed by Straka, only one from the Spiny thicket in the south of the island was collected. Yet, the pollen results presented taxa typical of this vegetation such as type Euphorbia (24,5%), type Acacia and they even found one pollen grain of an *Alluaudia ascendens* (Drake) Drake (Didiereaceae) and also a high percentage of Asteraceae (52%) (Straka 1991). Straka's analysis was however only qualitative and more advanced quantitative analysis are needed.

After almost three decades, seven samples from the top of sediment cores and surface samples were collected and analysed by Razafimanantsoa (2015) from the Northwest dry deciduous forest in Madagascar. These samples represented taxa from different soil types within the dry deciduous forest, but also the degraded dry forest and savannah ecosystems. Results showed the presence of high pollen rain concentration in the dry forest and savannah ecosystem compared to the degraded forest (Razafimanantsoa 2015). In the pollen results, the dry deciduous forest is characterised by *Commiphora* and *Dalbergia* as well as Rubiaceae type, while Poaceae and *Ziziphus* were abundant in the savannah. The degraded forest was on the other hand characterised by the abundance of *Eucalyptus* sp. These initial surface sample results by Burney (1988), Straka (1991) and Razafimanantsoa (2015) in addition to recently collected samples (fieldwork session in 2015, 2016 and 2019) from the succulent woodland, dry deciduous and sub-humid forest could form the basis to establish a reference based on the distribution of pollen and their representation in the various vegetation types in Madagascar.

Similar to these surface samples destined for palaeoecological interpretations, several investigations of pollen rain based on samples from spore Brutayert traps are important tools to help for the interpretation of past pollen record. Analysis of pollen samples from the Capital of Madagascar in the Central Highlands was first published as a thesis in the early 80' covering the period of 1979, 1980, 1981 (Rajeriarison 1983). This study found that the pollen in the region contains a high percentage of Poaceae which were interpreted by Straka (1991) to have reflected rice fields and savannah that are abundant in the region (Straka 1991).

## 21.6.2 Namibia

Namibian modern pollen has been recently studied by Tabares *et al.* (2018) who used soil surface samples to test the correspondence between vegetation and pollen in savannah ecosystems. They found that pollen is able to separate out distinct vegetation types such as *Acacia* woodland and open mixed woodland well, although overall species richness is not reflected well by pollen assemblages. Grazing pressure was found to be indicated by *Alternanthera*, *Tribulus*, and *Limeum* and the co-occurrence of *Dichrostachys*, *Phyllanthus* and *Crotalaria* is an indicator of environmental encroachment.

*Hyrax* dung middens, one of the few pollen records available from extreme arid environments such as the Namib desert, were investigated by Gil-Romera *et al.* (2006) and included four modern dung samples. These modern samples were found to be more widely variable than their fossilised equivalents, suggesting that they represented shorter time sampling periods than older dung extracted from middens.

## 21.7 SPATIAL SPREAD OF MODERN POLLEN STUDIES

The spatial distribution of modern pollen studies in tropical Africa is not even, with work being concentrated in certain areas and countries (Figure 1). Table 1 shows a breakdown of number
<table><caption>**Table 1.** Phytochoria and number of modern pollen studies that include samples from each Phytochoria (White 1983).</caption><thead><tr><th>Phytochoria<br>(White 1983)</th><th>Number of studies including<br>samples from this region</th></tr></thead><tbody><tr><td>I. Guineo-Congolian regional centre of endemism</td><td>39</td></tr><tr><td>II. Zambezian regional centre of endemism</td><td>5</td></tr><tr><td>III. Sudanian regional centre of endemism</td><td>16</td></tr><tr><td>IV. Somalia-Masai regional centre of endemism</td><td>14</td></tr><tr><td>VI. Karoo-Namib regional centre of endemism</td><td>2</td></tr><tr><td>VII. Mediterranean regional centre of endemism</td><td>1</td></tr><tr><td>VIII and IX. Afromontane archipelago-like regional centre of<br>endemism and extreme floristic impoverishment</td><td>7</td></tr><tr><td>X. Guineo-Congolia/Zambezia regional transition zone.</td><td>0</td></tr><tr><td>XI. Guinea-Congolia/Sudania regional transition zone.</td><td>1</td></tr><tr><td>XII. Lake Victoria regional mosaic.</td><td>8</td></tr><tr><td>XIII. Zanzibar-Inhambane regional mosaic.</td><td>0</td></tr><tr><td>XIV. Kalahari-Highveld regional transition zone.</td><td>0</td></tr><tr><td>XVI. Sahel regional transition zone.</td><td>11</td></tr><tr><td>XVII. Sahara regional transition zone.</td><td>5</td></tr><tr><td>XIX and XX East and West Malagasy regional centres of<br>endemism</td><td>4</td></tr></tbody></table>

of studies by Phytochoria, which demonstrates that within the tropical region of Africa, the Guineo-Congolian region is most represented, followed by the Sudanian region and the Sahel. These regions cover large areas of land, and are also important biologically, harbouring a very large number of species within multiple vegetation types. There are other comparably extensive phytochoria which are much less well represented. The Zambezian region, for instance, has very few studies but covers a large part of southern Africa. The Guineo-Congolian/Zambezian regional transition zone and the Kalahari-Highveld regional transition zone do not have any studies at all, and the Guinea-Congolia/Sudania regional transition zone has just one study.

It is also apparent, from Figure 1 (and Table 2) that large swathes of Africa have few to no studies, including much of central and central Southern Africa. Coastal regions are better represented than inland areas, and studies tend to be clustered in countries where foundational palaeoecological work had taken place, such as Uganda and Cameroon.

## 21.8 THE FUTURE OF MODERN POLLEN STUDIES IN AFRICA

### 21.8.1 Geographical and vegetation priority areas

Although the number of modern pollen rain studies in Africa has increased over the past few decades, many countries and vegetation types are still under-investigated (Figure 1). Some of these instances of under-representation, for instance in the Saharan region, are likely due to environmental factors like aridity, meaning that gathering modern pollen samples from soil is impractical and often unsuccessful. Any modern samples that are collected in the course of palaeoecological fieldwork will not necessarily coincide with flowering of ephemeral species that thrive in arid environments, potentially producing pollen that is dispersed rapidly and potentially
<table><caption>**Table 2.** Table showing studies consulted in this study including their number for Figure 1.</caption><thead><tr><th>Number</th><th>Area</th><th>Reference</th><th>Data collection</th><th>Focus of the Study</th></tr></thead><tbody><tr><td colspan="5" style="text-align: center; font-weight: bold;">WEST AFRICA</td></tr><tr><td>1</td><td>Mauritania</td><td>Romero et al. (2003)</td><td>Pollen traps</td><td>Palaeoecology</td></tr><tr><td>2</td><td>Senegal, Mauritania</td><td>Lézine and Hooghiemstra (1990)</td><td>Lake surface</td><td>Palaeoecology</td></tr><tr><td>3</td><td>Senegal, Mauritania, Ocean</td><td>Lézine and Hooghiemstra (1990)</td><td>Soil, river, marine mud surface samples</td><td>Palaeoecology</td></tr><tr><td>4</td><td>Senegal, Togo</td><td>Lézine and Edorh (1991)</td><td>Soil, river surface samples</td><td>Palaeoecology</td></tr><tr><td>-</td><td>Senegal, Mauritania</td><td>Lézine (1987)</td><td>Soil and river samples</td><td>Palaeoecology</td></tr><tr><td>5</td><td>Côte d'Ivoire</td><td>Ybert (1975)</td><td>Pollen traps</td><td>Palaeoecology</td></tr><tr><td>6</td><td>Côte d'Ivoire</td><td>Fredoux (1978)</td><td></td><td></td></tr><tr><td>7</td><td>Côte d'Ivoire</td><td>Caratini et al. (1987)</td><td></td><td>Palaeoecology</td></tr><tr><td>8</td><td>Côte d'Ivoire, Chad</td><td>Ybert (1980)</td><td>Glycerine slides</td><td>Aeropalynology</td></tr><tr><td>9</td><td>Ghana</td><td>Julier et al. (2019)</td><td>Pollen traps</td><td>Palaeoecology</td></tr><tr><td>10</td><td>Ghana</td><td>Maley (1983)</td><td>Lake surface samples</td><td></td></tr><tr><td>11</td><td>Ghana</td><td>Julier et al. (2017)</td><td>Pollen traps</td><td>Palaeoecology</td></tr><tr><td>12</td><td>Togo</td><td>Chalié et al. (1990)</td><td>Soil surface</td><td></td></tr><tr><td>13</td><td>Togo</td><td>Edorh (1986)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>14</td><td>Togo</td><td>Edorh and Afidegnon (2008)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>15</td><td>Bénin</td><td>Zanou et al. (2020)</td><td>Soil surface</td><td></td></tr><tr><td>16</td><td>Bénin</td><td>Tossou et al. (2012)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>17</td><td>Bénin</td><td>Tchabi et al. (2017)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>18</td><td>Bénin</td><td>Tossou et al. (2016)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>19</td><td>Niger</td><td>Caratini (1988)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>20</td><td>Nigeria</td><td>Adeniyi et al. (2018)</td><td>Pollen traps</td><td>Aeropalynology</td></tr></tbody></table>

(continued)
<table><caption>**Table 2. Continued.**</caption><thead><tr><th>Number</th><th>Area</th><th>Reference</th><th>Data collection</th><th>Focus of the Study</th></tr></thead><tbody><tr><td>21</td><td>Nigeria</td><td>Adekanmbi and Ogundipe (2010)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>22</td><td>Nigeria</td><td>Ajikah et al. (2015)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>23</td><td>Nigeria</td><td>Ibigbami and Adeonipekun (2020)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>24</td><td>Nigeria</td><td>Adeonipekun et al. (2016)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>25</td><td>Nigeria</td><td>Agwu (2001)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>26</td><td>Nigeria</td><td>Abdulrahaman et al. (2015)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>27</td><td>Nigeria</td><td>Ezikanyi et al. (2016)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>28</td><td>Nigeria</td><td>Agwu (1986)</td><td>Soil surface/ Water samples</td><td>Palaeoecology</td></tr><tr><td>29</td><td>Nigeria</td><td>Agwu and Osibe (1992)</td><td></td><td>Aeropalynology</td></tr><tr><td>30</td><td>Nigeria</td><td>Njokuocha (2006)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>31</td><td>Nigeria</td><td>Adekanmbi et al. (2018)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>32</td><td>Nigeria</td><td>Alebiosu et al. (2018)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>33</td><td>Nigeria</td><td>Salzmann (2000)</td><td>Pollen traps/ Soil surface</td><td>Palaeoecology</td></tr><tr><td>34</td><td>Nigeria</td><td>Salzmann and Waller (1998)</td><td>Pollen traps/ Soil surface</td><td>Palaeoecology</td></tr><tr><td>35</td><td>Chad</td><td>Schulz (1976)</td><td>Pollen traps</td><td>Palaeoecology</td></tr><tr><td>36</td><td>Chad</td><td>Maley (1972)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>37</td><td>Chad</td><td>Amaral et al. (2013)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>38</td><td>Chad</td><td>Maley (1981)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>—</td><td>Various</td><td>Melia (1984)</td><td>Filters and Marine</td><td>Aerobiology, Palaeoecology</td></tr><tr><td>—</td><td>Various</td><td>Hooghiemstra (1988)</td><td>Littoral and marine surface</td><td>Palaeoecology</td></tr><tr><td>—</td><td>Various</td><td>Lézine et al. (2009)</td><td>Various</td><td>Palaeoecology</td></tr><tr><td>—</td><td>Multiple</td><td>Dupont (1991)</td><td>Marine surface</td><td>Palaeoecology</td></tr><tr><td>—</td><td>Ocean</td><td>Calleja et al. (1993)</td><td>Filters</td><td>Palaeoecology</td></tr></tbody></table>

(continued)
<table><caption>**Table 2. Continued.**</caption><thead><tr><th>Number</th><th>Area</th><th>Reference</th><th>Data collection</th><th>Focus of the Study</th></tr></thead><tbody><tr><td>a</td><td>Various</td><td>Lézine (1997)</td><td>Littoral and Marine</td><td>Palaeoecology</td></tr><tr><td>b</td><td>Various</td><td>Caratini and Cour (1980)</td><td>Filters with silicon oil</td><td>Aeropalynology, Palaeoecology</td></tr><tr><td colspan="5"><strong>CENTRAL AFRICA</strong></td></tr><tr><td>39</td><td>Cameroon</td><td>Verlhac et al. (2018)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>40</td><td>Cameroon</td><td>Bengo (1992)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>41</td><td>Cameroon</td><td>Van Campo (2004)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>42</td><td>Cameroon</td><td>Reynaud-Farrera (1995)</td><td>Marine surface</td><td>Palaeoecology, Palynology</td></tr><tr><td>43</td><td>Cameroon</td><td>Lebamba et al. (2009)</td><td>Core top</td><td>Palaeoecology</td></tr><tr><td>44</td><td>Cameroon</td><td>Bengo (1996)</td><td>Soil surface</td><td>Palaeoecology, Palynology</td></tr><tr><td>45</td><td>Cameroon</td><td>Bengo et al. (2020)</td><td>Soil surface</td><td>Palaeoecology, Palynology, Hydrology</td></tr><tr><td>46</td><td>Cameroon</td><td>Vincens et al. (2000)</td><td>Soil surface</td><td>Modern pollen-vegetation relationships, Palynology</td></tr><tr><td>47</td><td>Central African Republic</td><td>Aleman et al. (2012)</td><td>Soil surface and superficial litter</td><td>Modern pollen-vegetation relationships, Palaeoecology</td></tr><tr><td>48</td><td>Gabon, Cameroon</td><td>Lebamba et al. (2009)</td><td>Soil surface</td><td>Palaeoecology, Palynology</td></tr><tr><td>49</td><td>Gabon</td><td>Ngomanda et al. (2007)</td><td>Soil surface and superficial litter</td><td>Palaeoecology, Palynology</td></tr><tr><td>50</td><td>Gabon</td><td>Henga-Botsikabobe (2015)</td><td>Soil surface</td><td>Modern pollen-vegetation relationships, Palaeoecology</td></tr><tr><td>51</td><td>Gabon</td><td>Henga-Botsikabobe et al. (2020)</td><td>Soil surface</td><td>Modern pollen-vegetation relationships, Palaeoecology, Palynology</td></tr><tr><td>52</td><td>Gabon</td><td>Jolly et al. (1996)</td><td>Soil surface</td><td>Modern pollen-vegetation relationships</td></tr></tbody></table>

(continued)
<table><caption>**Table 2. Continued.**</caption><thead><tr><th>Number</th><th>Area</th><th>Reference</th><th>Data collection</th><th>Focus of the Study</th></tr></thead><tbody><tr><td>-</td><td>Gabon</td><td>Ngomanda (2005)</td><td></td><td></td></tr><tr><td>53</td><td>Republic of Congo</td><td>Tovar et al. (2019)</td><td>Soil surface</td><td></td></tr><tr><td>54</td><td>Republic of Congo</td><td>Elenga (1992)</td><td>Surface samples</td><td></td></tr><tr><td>55</td><td>Republic of Congo</td><td>Elenga et al. (2000)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>56</td><td>Democratic Republic of Congo</td><td>Beuning et al. (2004)</td><td>Soil surface and core top</td><td>Palaeoecology</td></tr><tr><td>d</td><td>Marine, Gulf of Guinea</td><td>Dupont et al. (1998)</td><td>Soil surface and core top</td><td>Palaeoecology</td></tr><tr><td colspan="5" style="text-align: center; font-weight: bold;">EAST AFRICA</td></tr><tr><td>57</td><td>Sudan</td><td>El Ghazali (2002)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>58</td><td>Sudan</td><td>El Ghazali and Moore (1998)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>59</td><td>Djibouti</td><td>Bonnefille et al. (1980)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>60</td><td>Ethiopia</td><td>Bonnefille (2004)</td><td>Soil surface</td><td>Archaeology</td></tr><tr><td>61</td><td>Ethiopia, Tanzania</td><td>Barboni et al. (2019)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>62</td><td>Ethiopia</td><td>Bonnefille et al. (1987)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>63</td><td>Ethiopia, Kenya, Burundi</td><td>Roeland et al. (1988)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>64</td><td>Ethiopia</td><td>Bonnefille et al. (1993)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>65</td><td>Ethiopia</td><td>Mohamed Umer et al. (2004)</td><td></td><td>Archaeology</td></tr><tr><td>66</td><td>Kenya</td><td>Vincens (1984)</td><td></td><td>Palaeoecology</td></tr><tr><td>67</td><td>Kenya</td><td>Vincens et al. (2006)</td><td></td><td>Palaeoecology</td></tr><tr><td>68</td><td>Kenya</td><td>Tiercelin et al. (1987)</td><td></td><td></td></tr><tr><td>69</td><td>Kenya</td><td>Rucina (2000)</td><td>Soil surface/ Moss polster</td><td>Palaeoecology</td></tr><tr><td>70</td><td>Kenya, Tanzania</td><td>Coetzee (1967)</td><td></td><td>Palaeoecology</td></tr><tr><td>71</td><td>Uganda</td><td>Vincens et al. (1997)</td><td>Soil surface</td><td>Palaeoecology</td></tr></tbody></table>

(continued)
<table><caption>**Table 2. Continued.**</caption><thead><tr><th>Number</th><th>Area</th><th>Reference</th><th>Data collection</th><th>Focus of the Study</th></tr></thead><tbody><tr><td>72</td><td>Kenya, Uganda</td><td>Hedberg (1954)</td><td>Moss/Lichen polsters</td><td>Palaeoecology</td></tr><tr><td>73</td><td>Uganda</td><td>Hamilton (1972)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>74</td><td>Uganda, Kenya</td><td>Hamilton and Perrott (1980)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>75</td><td>Tanzania, Kenya, Uganda, Ethiopia, Somalia</td><td>Bonnefille et al. (1992)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>76</td><td>Uganda</td><td>Marchant and Taylor (2000)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>77</td><td>Uganda</td><td>Marchant et al. (1997)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>78</td><td>Tanzania</td><td>Schüler et al. (2014)</td><td>Pollen traps</td><td>Palaeoecology</td></tr><tr><td>79</td><td>Tanzania</td><td>Ivory and Russell (2016)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>80</td><td>Tanzania</td><td>Vincens (1987)</td><td>Core top</td><td>Palaeoecology</td></tr><tr><td>81</td><td>Burundi</td><td>Bonnefille and Riollet (1988)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>82</td><td>Tanzania</td><td>Schüler (2013)</td><td>Surface samples</td><td>Palaeoecology</td></tr><tr><td>83</td><td>Tanzania</td><td>Vincens et al. (2006)</td><td>Soil surface, pollen trap, core top</td><td>Palaeoecology</td></tr><tr><td>84</td><td>Malawi</td><td>Meadows (1984)</td><td>Lake surface</td><td>Palaeoecology</td></tr><tr><td>85</td><td>Malawi</td><td>DeBusk (1997)</td><td>Lake surface</td><td>Palaeoecology</td></tr><tr><td colspan="5" style="text-align: center; font-weight: bold;">SOUTHERN AFRICA</td></tr><tr><td>86</td><td>Madagascar</td><td>Razafimanantsoa (2015)</td><td>Soil surface</td><td>Modern pollen-vegetation relationships</td></tr><tr><td>87</td><td>Madagascar</td><td>Ramavovololona (1986)</td><td>Pollen traps</td><td>Aeropalynology</td></tr><tr><td>88</td><td>Madagascar</td><td>Rajeriarison (1983)</td><td>Pollen traps</td><td>Aerobiology</td></tr><tr><td>89</td><td>Madagascar and Mascareings</td><td>Straka (1991)</td><td>Soil surface/ moss polster</td><td>Modern pollen-vegetation relationships</td></tr><tr><td>90</td><td>Madagascar</td><td>Burney (1988)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>91</td><td>Namibia</td><td>Tabares et al. (2018)</td><td>Soil surface</td><td>Palaeoecology</td></tr><tr><td>92</td><td>Namibia</td><td>Gil-Romera et al. (2006)</td><td>Dung</td><td>Palaeoecology</td></tr></tbody></table>

<footnote>* Note that publications that are inaccessible but whose existence is confirmed by citations, or their inclusion in revision works are in italics.</footnote>
destroyed due to dryness and heat. This problem of aridity could be addressed by setting arti-
ficial pollen traps. Transitional zones between different phytochoria are also under-represented,
possibly due to their relatively small geographical extent. These areas should, however, receive
attention in future studies due to their potential value in developing understanding of vegetation
responses to climate change over time. The transitions between phytochoria such as the Guineo-
Congolian region, the Sudanian region, and the Sahel, for instance, are likely to have shifted
in the past in response to climate drivers (Salzmann and Hoelzmann 2005; Watrin et al. 2007).
The pollen assemblages at the boundaries of these phytochoria are, therefore, important for the
interpretation of shifts observed in fossil pollen records such as that from Lake Bosumtwi (Miller
et al. 2016) and marine cores (Dupont and Agwu 1992).

**21.8.2 Methodological recommendations for pollen dispersal and deposition modelling**

The goal of pollen analysis has since the earliest days of the discipline been the reconstruction of past landcover, but the relationship between pollen assemblage at a point and surrounding vegetation is not simple. There are three broad methods for using modern pollen and vegetation data to improve interpretation of sedimentary pollen records. The first method, biomisation, assigns pollen types to plant functional types, then using the plant functional type spectrum to assign a biome, on the assumption that biomes are persistent features of the vegetation (Jolly et al. 1998; Vincens et al. 2006). Biomisation results are used in the validation of vegetation models such as Dynamic Global Vegetation Models (Hély et al. 2006). The second method, the modern analogue technique, statistically matches fossil pollen assemblages to the nearest modern pollen assemblage, and the past environment then assumed to be the same as the present one (Peyron et al. 2006). The third method, pollen-vegetation relationship modelling, uses a model of pollen dispersal and deposition (pdd) to establish a relationship between landcover and pollen assemblage, then applies an inverse form of this to reconstruct past land cover (Duffin and Bunting 2008; Gillson and Duffin 2007; Sugita 2007a, 2007b).

Here, we focus on the pdd model and how studies of modern pollen rain in tropical Africa
could improve its applicability and relevance. The pdd modelling approach to landcover recon-
struction reconstructs the wider past landscape (Bunting and Middleton 2009; Sugita 2007a,
2007b), by assuming that the relationship between plant and pollen is constant over time. The
technique has been developed extensively over the last decade and is becoming a valuable tool
for investigations of patterns of and controls on land cover change, especially in the northern
temperate zone (e.g. Marquer 2017; Li et al. 2020).

Challenges in extending the pdd approach (and the modern analogue approach) to the tropics
are two-fold-collecting calibration datasets of modern pollen and associated vegetation data,
and the development of appropriate pollen dispersal models. Identifying appropriate trapping
techniques in tropical ecosystems can be difficult; many ecosystems lack natural pollen traps
such as moss polsters, and some ecosystems are too arid or fire-impacted to allow multi-year trap
placement and recovery, which has been shown to be advantageous in tropical systems (Haselhorst
et al. 2020). Collecting vegetation data for comparison with the modern pollen data is also often
a challenge (Bunting et al. 2013). Existing vegetation maps may not be at appropriate scale,
woody plants may only be recorded above 10 cm DBH, which excludes some that may flower
thereby contributing to the pollen signal, and vegetation surveys hampered by difficult terrain
and incomplete or challenging taxonomy. Dispersal models often fail to incorporate zoophilous
taxa, although reducing the number of taxa used in studies can go some way to solving this issue
(Whitney et al. 2019).

Despite these challenges, research is underway in tropical and sub-tropical areas to develop
means of applying the pdd modelling approach to reconstruction of land cover from pollen
records. It has considerable potential in improving the integration of palaeoecology with ecology, archaeology and climate modelling (e.g. Harrison *et al.* (2020)), adding a long term perspective critical to meet socioecological challenges such as planning for climate change adaptation and mitigation.

This review can support the use of pdd modelling in African palnology by showing the
range of data available across the continent. Existing pollen datasets can be identified in locations
where it may be possible to extract suitable vegetation data from remote sensing and data collected
for other purposes, and achieve initial model calibration for major habitats. We also hope to alert
colleagues to the potential of modern pollen samples, and therefore encourage study design which
can be used for model testing and calibration as well as for the analyst's primary purpose.

21.9 CONCLUSIONS

In this review, we have collated and described modern pollen work conducted in tropical Africa to date. We have provided country-scale summaries of the literature and identified potential areas for future work, including arid regions and transitional regions. If these areas are focussed on in forthcoming work, a more complete understanding of pollen-vegetation relationships in tropical Africa will be developed, which will in turn contribute to improved interpretations of fossil pollen records. Further, targeted modern pollen studies, designed with quantitative modelling approaches in mind will also allow more rigorous interpretations of pollen fossil records to be developed for Africa.

21.10 ACKNOWLEDGEMENTS

We would like to thank Dr. Anne-Marie Lézine and Prof. Henry Hooghiemstra for kindly sharing papers and information that greatly helped this review. Prof. Christelle Hély and an anonymous reviewer also provided helpful and detailed comments that significantly improved the work, for which we are extremely grateful. ACMJ acknowledges funding from the NRF African Origins Platform (117666). SM from the NRF Competitive Programme for Rated Researchers (118538). ER acknowledges The Southern African Science Service Centre for Climate Change and Adaptive Land Management (SASSCAL, 466418 c/c BIO1056) and the University Research Committee accredited (URC) from the University of Cape Town (2020). DH acknowledges funding by CongoPeat, a NERC Large Grant (NE/R016860/1) to Simon L. Lewis.

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<figure><img src="image_117.png" /></figure>

Taylor & Francis

Taylor & Francis Group

http://taylorandfrancis.com
CHAPTER 22

Vegetation response to millennial- and
orbital-scale climate changes in Africa: A view
from the Ocean

Ilham Bouimetarhan<fnref n="1" />

*Faculté des Sciences appliquées, CUAM, Ibn Zohr University,*
*Agadir, Morocco*

Lydie Dupont

MARUM - Center for Marine Environmental Sciences, University of Bremen,
28359 Bremen, Germany

Hanane Reddad

L'Ecole Supérieure de Technologie & Faculté des Lettres et des Sciences Humaines, Sultan Moulay Slimane University, Beni Mellal, Morocco

Asmae Baqloul

Faculté des Sciences, Ibn Zohr University, Agadir, Morocco

Anne-Marie Lézine

Laboratoire d'Océanographie et du Climat, Expérimentation et Approche
numérique/IPSL, Sorbonne University, CNRS-IRD-MNHN, Paris, France

ABSTRACT: Pollen from deep-sea sedimentary archives have proved to be a particularly use-
ful tool to provide an integrated regional reconstruction of vegetation and climate (temperature,
precipitation, and seasonality) on the adjacent continent throughout the Earth's climate history.
In this paper, we have compiled marine pollen records from the African margin in order to assess
long-term patterns of vegetation changes during climate cycles. We investigate the changing and
complex interplay between African climate and high- and low-latitude forcing at orbital and mil-
lennial timescales. More importantly, the study of those records has shown the extent of different
biomes during the last ten million years covering the Plio-Miocene, glacial-interglacial cycles,
as well as eight Heinrich Stadials, the last deglaciation and the Holocene. In the West African
records, arboreal pollen expanded during most interglacials and during the early Holocene. The

<footnote n="1">¹Other affiliation: MARUM-Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany</footnote>
savannah and semi-desert/desert vegetation expanded abruptly during glacials, Heinrich Stadials and the Last Glacial Maximum. Most eastern African pollen records have shown a clear dominance of arboreal taxa throughout all climate cycles except during MIS32 suggesting that a decoupling between eastern and western Africa took place. However, the scarcity of eastern African marine pollen records hampers a reliable comparison between these two sectors.

## 22.1 INTRODUCTION

The distribution and composition of the African vegetation is largely controlled by climate primarily through temperature ranges, radiation and precipitation (e.g. Box 1981; Holdridge 1947; Woodward and Williams 1987; Woodward and McKee 1991). In turn, vegetation can exert an important influence on surface energy fluxes and the hydrological cycle through alteration of the surface albedo and biogeochemical processes, thus affecting climate locally (Denman et al. 2007; Pielke et al. 1998). In Africa, a continent that represents around 20% of the Earth's surface, and where climate and vegetation data are sparse, our understanding of the vegetation-climate interaction and its consequences on the composition, structure and maintenance of terrestrial ecosystems remains poor. Spanning the equator and encompassing tropical, sub-tropical and temperate climate systems of both hemispheres, Africa provides a unique opportunity to study not only local and regional climate dynamics, but also to investigate and understand vegetation-climate interactions. Thus, allowing feedback effects to be identified on different spatial and temporal scales, and to assess the inter-hemispheric teleconnections in the global climate system. In this paper, we review the current state of knowledge related to African vegetation change over the entire Quaternary (2.6 million years) and older at orbital, millennial and centennial timescales by reviewing a large set of fossil pollen records obtained from marine sediments.

It is well established that the study of fossil pollen contained in sediments facilitates the reconstruction of terrestrial palaeoenvironmental changes through geological times, and constitutes the most widely used quantitative proxy of past vegetation changes (Gajewski 1993; Webb 1986). Pollen grains can be transported over long distances by winds and/or by rivers, and consequently reach the sea floor. Therefore, pollen are present in marine sediments from estuarine to abyssal environments and from the tropics to the Polar Regions. Consequently, their broad occurrence makes them valuable palaeoclimatic and palaeoenvironmental markers especially along the coast of arid environments where terrestrial records are scarce and organic microfossils are badly preserved. Pollen data derived from marine sediments integrate palynological information on large shifts in vegetation over long and continuous periods, with individual sequences of sediments often spanning more than one glacial/interglacial climatic cycle. Pollen records obtained from marine sediments have been shown to be suitable for tracing large-scale climatically related vegetation changes (Hooghiemstra 1988), hydrological variability (Dupont 1999), and for correlations between change on land and in the oceans (Heusser and Shackleton 1979; Hooghiemstra et al. 2006). However, the interpretation of pollen records from marine sediments should be done carefully accounting for several aspects. These include: (i) source and production of pollen grains, because it varies remarkably from one species to another, (ii) transport to the ocean floor and through the water column, (iii) displacement by ocean currents, (iv) sedimentation process, (v) taphonomic processes and early diagenesis, and (vi) fossilization in the sediment (Dupont 1999).

Pollen grains are dispersed over long distances (up to 200 km) reflecting the ease with which they can be transported from their source area to the site of sedimentation (Wright 1952). Therefore, the evaluation of transport agents is particularly important in the interpretation of marine pollen records. Aeolian transport of pollen grains predominates in deep-sea sediments located far from the coast and along arid areas with no or small river discharge (Heusser and
Morley 1985; Hooghiemstra *et al.* 1986), whereas fluvial transport is especially dominant in humid areas and at sites close to river mouths (Hooghiemstra *et al.* 1992).

By reviewing a large set of African vegetation reconstructions based on deep-sea pollen records along the African ocean margins both in low- and mid-latitudinal climatic regions of both hemispheres, we intend to: (i) assess the impact, timing and amplitude of climate changes on the regional vegetation, (ii) study the large-scale vegetation changes, (iii) compare the hydrological variability between the northern and southern hemisphere, and (iv) map the tree pollen distribution through geological times. Specifically, this synthesis will allow us to trace past changes in the African vegetation and to investigate the difference between the variability of tropical/equatorial vegetation and subtropical vegetation (north and south of the equator).

## 22.2 CLIMATIC AND OCEANOGRAPHIC SETTINGS AND THEIR IMPACTS ON POLLEN TRANSPORT

The climate of Africa includes a range of several different types that vary more in rainfall amount than in temperatures (Nicholson and Grist 2003). Owing to its position across equatorial and subtropical latitudes in both the northern and southern hemisphere we can distinguish the equatorial climate, the tropical wet and dry climates, the tropical monsoon climate, the semi-desert climate (semi-arid), the desert climate (hyper-arid and arid), the subtropical climate and highland climate.

Most of the continent lies within the intertropical zone between the Tropic of Cancer and the Tropic of Capricorn. The climate of Africa depends on the seasonal migration of the tropical rainbelt associated to the Intertropical Convergence Zone (ITCZ). The ITCZ is a seasonally migrating low-pressure belt that forms where the Northeast (NE) Trade Winds converge with the Southeast (SE) Trade Winds (Nicholson and Grist 2003). During boreal summer, between July and September, the ITCZ reaches its northernmost position bringing moist air upward. This causes water vapour to condense resulting in a band of heavy precipitation over the northern tropical-subtropical areas as a humid monsoon flow bringing most of the annual rainfall (Nicholson and Grist 2003). A contrasting dry season develops during the boreal winter, from December to February, when the ITCZ reaches its southernmost position causing dry conditions in the northern subtropics associated with strong NE Trade Winds and humid conditions in the southern subtropical regions.

The northernmost and the southernmost edges of the continent have a Mediterranean climate controlled respectively by variations in the North Atlantic Oscillation (NAO) (Le Houérou *et al.* 1986) and by the position and strength of the South Atlantic anticyclone and the Indian Ocean anticyclone (Shannon 1985; Shannon and Nelson 1996). The climate of Africa is predominantly tropical due to its latitudinal position in relation to the equator and the tropics (Nicholson 2000). Temperate climates are rare across the continent except at high elevations and along the edges.

African deserts are the sunniest and the driest parts of the continent, owing to the prevailing presence of the subtropical ridge with subsiding, hot, dry air masses such as the Saharan Air Layer (SAL), a mid-tropospheric zonal wind system occurring at higher altitudes (1500–5500 m), incorporating the African Easterly Jet (AEJ). SAL is responsible for transporting dust and terrestrial remains such as pollen grains from the Sahara and Sahel belt to the Atlantic Ocean (Colarco *et al.* 2003; Hooghiemstra *et al.* 1986; Prospero and Nees 1986; Prospero *et al.* 2002; Stuut *et al.* 2005).

The coast of the Gulf of Guinea, in tropical and equatorial Africa, is characterized by high rainfall and consequently several river systems that complement the aeolian transport of pollen grains. Therefore, fluvial-transported pollen is expected to dominate the pollen assemblages found in marine sediments offshore tropical rivers such as Senegal, Niger, Congo and Cunene Rivers. Further south, the climate system of southern Africa is controlled by the position and
<figure><img src="image_118.png" /><figcaption>**Figure 1.** Map of the modern vegetation simplified after White (1983) with the locations of all African marine sites.</figcaption></figure>

strength of the South Atlantic anticyclone and the Indian Ocean anticyclone (Shannon 1985; Shannon and Nelson 1996). The pressure difference between the South Atlantic anticyclone and the continental pressure field causes alongshore SE trade winds (Figure 1). SE trade winds are the main transport agent of pollen from Namibia and western South Africa. Orange River has shown little to no contribution to the pollen content of the adjacent marine sites (Meadows *et al.* 2002). Along the SE African coast, conditions are dominantly warm and moist, due to the influence of the warm Indian Ocean and Agulhas Western Boundary Current. Moisture is advected from the tropical Indian Ocean mainly during summer months when precipitation often exceeds 100 mm per month (Nash and Meadows 2012) in north-eastern South Africa (Tyson 1986; Tyson and Preston-Whyte 2000). Fluvial transport of pollen grains by Limpopo and Zambezi Rivers is also considerable in this area. Regarding the Gulf of Aden site, the area is dominated by the Indian monsoon (Almogi-Labin *et al.* 2000).

The wind systems influence the most important large-scale oceanographic features along the African continent. The Canary Current, a wind-driven surface current that is part of the North Atlantic Gyre, dominates the ocean circulation in northwest Africa. This eastern boundary current branches south from the North Atlantic Current due to intensified NE trade winds and flows
southwest about as far as Senegal where it turns west and later joins the Atlantic North Equatorial Current. Further south, the west coast of southern Africa is dominated by the northward flowing Benguela Coastal Current (BCC) stretching from 34°S to 15°S. The SE African continental shelf is dominated by the Agulhas Current. Hooghiemstra *et al.* (2006) suggests that the distribution of pollen over the ocean surface is reflected in the marine sediments without substantial displacement by marine currents. This might not be fully true (Fischer *et al.* 2009), but isopollen maps show that on continental scales the displacement by ocean currents is not large enough to bias the trends seen in the pollen distribution (Dupont and Agwu 1991; Hooghiemstra *et al.* 1986). We therefore assume that no large-scale transport has displaced the palynomorphs and other terrigenous material while sinking through the water column.

Modern vegetation distribution in Africa reflects the north-south precipitation gradient (Figure 1). The present-day African vegetation around the equator consists of tropical forests including evergreen rainforest in the Congo basin and in the moist part of West Africa and semi-evergreen and deciduous forest in northern Cameroon and southern Congo. North and south of the forest fringes there is a narrow belt of natural grass savannah. North of the xerophytic shrubland of the Sahel zone and along the coast of Namibia and southwest Angola, desert vegetation occurs (White 1983). Mediterranean vegetation containing trees and shrubs dominate the northern and the southernmost regions of Africa. Coastal vegetation is represented by mangrove, occurring in tropical/subtropical estuaries and near the river mouths (White 1983). The distribution of mangrove depends on water salinity, river runoff, and humidity (Blasco 1984).

## 22.3 COMPILATION OF THE RECORDS

In this study, we use all the available marine pollen records from Africa with an appropriate age model stored in the African Pollen Database (APD) and Pangaea as well as those delivered by authors upon request. Out of 95 marine sites illustrated in Figure 1, only 60 pollen records have the potential to document the vegetation response to climate variability and, therefore, have been used in this paper (Supporting Online Material [SOM] Appendix Table 1).

All of the radiocarbon-dated records considered here have age models in calendar years (cal kyr BP) after conversion of ¹⁴C dates to calendar age according to Stuiver *et al.* (2020). The age models were directly retrieved from the published articles or from the APD (i.e. based on linear interpolation between the dated samples) taking into account the marine reservoir age of 400 years, which reflects the present-day global average (Hughen *et al.* 2004). Age models beyond the limit of radiocarbon dating were based on the marine oxygen isotope stratigraphy. Selected sites with sufficient temporal resolution were used to illustrate the different patterns of the vegetation response to major climatic events in a centennial-, millennial- and orbital-time scale (Figures 2, 3 and 4). The whole dataset was then used to map tree pollen distribution in marine sediments off African shores at a continental scale throughout different climate cycles (Figure 5). Tree pollen types include trees, shrubs, palms and lianas. Percentages are calculated against a sum of total pollen excluding those of aquatics (including Cyperaceae) and *Pinus* (SOM Appendix Table 2).

## 22.4 PATTERN OF VEGETATION CHANGES IN AFRICA

Here, we focus on changes in pollen records during four main time intervals; the last deglaciation, the last glacial cycle, the mid-Pleistocene and the Plio-Miocene. To be selected for further analysis, the sites had to cover at least parts of these intervals, with a sufficient temporal resolution for a substantial part of the record, and sufficient age control to pinpoint centennial- or millennial-scale changes. Only eight records of the last deglaciation, eight records of the last glacial cycle,
<figure><img src="image_119.png" /><figcaption>**Figure 2.** Summary diagrams showing a south-north transect of vegetation changes during the last deglaciation, using the groups given in Table 1, for African marine sites (right hand axes: eastern African margin, left hand axes: western African margin). Additional indicators such as Poaceae (corn yellow) and *Podocarpus* pollen (lila) are shown for each site in percentages of total pollen (Y-axes). Note the absence of *Podocarpus* pollen in the northern records. YD: Younger Dryas, BA: Bølling-Allerød warm event, HS1: Heinrich Stadial 1, LGM: Last Glacial Maximum. Black vertical lines are denoting the LGM, HS1, BA, YD and the Holocene for each record.</figcaption></figure>
<figure><img src="image_120.png" /></figure>

**Figure 3.** Summary diagrams showing a south-north transect of vegetation changes during the last glacial cycle, using the groups given in Table 1, for African marine sites (right hand axes: eastern African margin, left hand axes: western African margin). Additional indicators such as Poaceae (corn yellow) and *Podocarpus* pollen (lila) are shown for each site in percentages (Y-axes). Note the absence of *Podocarpus* pollen in the northern records. MIS: Marine isotope stage. Black vertical lines are delimiting MIS5, MIS4 and MIS3 for each record.
<figure><img src="image_121.png" /><figcaption>**Figure 4.** Summary diagrams showing a south-north transect of vegetation changes during (A) the Mid-Pleistocene, and (B) the Plio-Miocene using the groups given in Table 1, for African marine sites (right hand axes: eastern African margin, left hand axis: western African margin. Additional indicators such as Poaceae (corn yellow) and *Podocarpus* pollen (lila) are shown for each site in percentages (Y-axes). MIS: Marine isotope stage. Black vertical lines are delimiting the different MISs in Figure 4A and are separating the Miocene, the Pliocene and the early Pleistocene in Figure 4B.</figcaption></figure>
three mid-Pleistocene and four Plio-Miocene records met these criteria (Figure 2, 3 and 4). Differences in regional floras make it difficult to compare pollen records from different regions directly. To facilitate comparisons between sites, the vegetation records are summarized in terms of major vegetation types (biomes) (Table 1). This naturally involves a certain loss of information, but allows us to describe the main vegetation changes for each record (Figure 2, 3 and 4) in a consistent way. It also should be kept in mind that the selection of pollen types reduces the sums on which percentage calculation is based.

<figure><img src="image_122.png" /></figure>

(Continued)
<figure><img src="image_123.png" /><figcaption>**Figure 5.** Spatial distribution of tree pollen percentages in African marine sediments. Four categories are considered. Black dot: AP>45% showing high percentages of arboreal taxa, grey dot: 15<AP<45% intermediate percentages of arboreal taxa, light grey dot: AP<15% weak percentages of arboreal taxa and white dot: AP=0% absence of arboreal taxa. Dashed boxes, indicate cold stages and solid boxes denote warm stages.</figcaption></figure>

### 22.4.1 Last deglaciation and Holocene

The ODP1078C from southwestern (SW) Africa (Dupont *et al.* 2008) and MD92-1002 from eastern Africa in the Gulf of Aden (Fersi *et al.* 2016) provide continuous pollen records of the last 20,000 years with high temporal resolution (SOM Appendix Table 1, Figure 2). The other pollen records cover either the early part of the last deglaciation or the Holocene (Figure 2).
<table><caption>**Table 1.** List of the African biomes and characteristic pollen taxa grouped in major vegetation types according to the phytogeographical assignment.</caption><thead><tr><th>Mega-Biome</th><th>Equivalent local vegetation names</th><th>Characteristic pollen taxa</th></tr></thead><tbody><tr><td>Temperate/</td><td>Cool temperate rain forest</td><td>Azioaceae, <i>Cedrus</i>, <i>Ericaceae</i>, <i>Juniperus</i>, <i>Olea</i>, <i>Pinus</i>, <i>Pistacia</i>, <i>Quercus</i>, Restionaceae</td></tr><tr><td>Mediterranean forest</td><td>Warm-temperate forest</td><td></td></tr><tr><td rowspan="2">Semi-desert/Desert</td><td>Fynbos</td><td rowspan="2"><i>Artemisia</i>, <i>Asteroideae</i>, <i>Cichoroideae</i>, <i>Ephedra</i>, <i>Plantago</i>, <i>Ziziphus</i>, <i>Zygophyllum</i></td></tr><tr><td>Desert shrubs</td></tr><tr><td rowspan="2">CCA</td><td>Grass</td><td rowspan="2">Amaranthaceae, Caryophyllaceae</td></tr><tr><td>Herbs</td></tr><tr><td>Savannah</td><td>Desert and halophytic vegetation</td><td><i>Acacia</i>, <i>Spermacoce</i>, <i>Boscia</i>, <i>Celtis</i>, <i>Cleome</i>, <i>Mimosaceae</i>, <i>Mitracarpus</i></td></tr><tr><td rowspan="4">Mangrove Tropical forest</td><td>Steppe</td><td></td></tr><tr><td>Savannah</td><td></td></tr><tr><td>grassland</td><td></td></tr><tr><td>Mangrove</td><td><i>Avicennia</i>, <i>Rhizophora</i></td></tr><tr><td rowspan="4"></td><td>Tropical lowland forest</td><td><i>Alchornea</i>, <i>Allophylus</i>, <i>Arecaceae</i></td></tr><tr><td>Tropical evergreen forest</td><td><i>Berlina</i>/<i>Isoberlina</i>, <i>Bignoniaceae</i>, <i>Blighia</i>, <i>Bombacaceae</i>, <i>Borassus</i>, <i>Brachystegia</i>, <i>Butyrospermum</i>, <i>Canthium</i>, <i>Capparis</i>, <i>Cassia</i>, <i>Combretaceae</i>, <i>Croton</i>, <i>Cuviera</i>, <i>Daniellia</i>, <i>Diospyros</i>, <i>Dodonaea</i>, <i>Elaeis</i>, <i>Ficus</i>, <i>Gaertnera</i>, <i>Hippocrateaceae</i>, <i>Hygrophila</i>, <i>Hymenocardia</i>, <i>Ilex</i>, <i>Indigofera</i>, <i>Ixora</i>, <i>Lannea</i>, <i>Leea</i>, <i>Mallotus</i>, <i>Manilkara</i>, <i>Melochia</i>, <i>Ochna</i>, <i>Parinari</i>, <i>Phoenix</i>, <i>Phyllanthus</i>, <i>Piliostigma</i>, <i>Pterocarpus</i>, <i>Rhamnaceae</i>, <i>Rhus</i>, <i>Schreberea</i>, <i>Sterculia</i>, <i>Stereospermum</i>, <i>Syzygium</i>, <i>Tamarindus</i>, <i>Tarenna</i>, <i>Trichilia</i>, <i>Uapaca</i>, <i>Urticaceae</i>, <i>Vitaceae</i>, <i>Ximenia</i>, <i>Zanthoxylum</i></td></tr><tr><td>Tropical semi-deciduous forest</td><td></td></tr></tbody></table>
In Equatorial Africa, the pollen record of T89-16 (Marret *et al.* 2001) (Figure 2) provides information into the equatorial vegetation development reflecting environmental changes in the Congo basin prior to the Holocene. We excluded core KW 31, located south of the Niger Delta (Lézine and Cazet 2005), despite a sufficient time resolution due to substantial gaps in the pollen record (SOM Appendix Table 1). The GeoB9508-5 off the Senegal River and GeoB12624-1 off the Rufiji Delta, (Bouimetarhan *et al.* 2012; 2015) show high-resolution vegetation change during the northern hemisphere cold Heinrich Stadial 1 (HS1; c. 18-15 kyr BP) (McManus *et al.* 2004) and the Younger Dryas (YD; c. 12.9-11.6 kyr BP) (Rasmussen and Thomsen 2015) (Figure 2). The Holocene records are represented by the high-resolution GeoB8331-4 and GeoB7920-2 pollen records (Dupont and Schefuß 2018; Zhao *et al.* 2016) covering the last 10,000 years and the GeoB8601-3 pollen record covering the last 3000 years (Zhao *et al.* 2019) (Figure 2).

In southern Africa, the ODP1078C pollen record off the coast of Namibia and Angola shows a clear dominance of semi-desert vegetation and Poaceae during the Last Glacial Maximum (LGM), which decreases slightly during the Heinrich Stadial (HS) 1 while tropical forest and mangrove as well as *Podocarpus* increased, indicating wetter and cooler climate conditions. This trend is almost stable until the Holocene. However, from 10 to 8 kyr BP, a slight increase in mangrove is observed reflecting a continuous input freshwater supply, which decreases in favour of the tropical forest and *Podocarpus* (reaching up to 54%) from 8 until 3 kyr BP. After 3 kyr BP Poaceae increase rapidly up to 40% possibly reflecting a shift towards drier conditions, although human impact cannot be excluded.

In eastern Africa, the MD92-1002 pollen record from the Gulf of Aden shows rather a contrasting trend. The last deglacial vegetation is dominated mainly by CCA (Caryophyllaceae and Amaranthaceae including Chenopodiaceae) and Poaceae. CCA reach up to ~58% and 45% during HS1 and YD respectively along with semi-desert/desert vegetation indicating the extremely dry climatic conditions during the North Atlantic cold stadials. A slight increase in the savannah is observed during the time period equivalent to the northern hemisphere warm event known as the Bølling-Allerød (BA; c. 14.7 to 12.8 kyr BP) (Rasmussen *et al.* 2006). The onset of the Holocene (c. 11.7 kyr BP) exhibits a substantial decrease in CCA and semi-desert representation along with an increase in savannah elements as well as the tropical forest and mangrove indicating a shift towards relatively wetter climatic conditions until 5 kyr BP. *Podocarpus* pollen is present in very low relative abundances during the BA and late Holocene testifying rather the long-distance wind transport.

In equatorial Africa, the pollen record off the Congo River T89-16 shows a constant dominance of the mangrove forest throughout the whole sequence reaching up to 78% during the YD. High abundances of mangrove pollen have been associated with transgressive phases and large flood of the Congo River (Scourse *et al.* 2005). Poaceae and *Podocarpus* exhibit simultaneously higher percentages during the LGM indicating cooler climate and decrease dramatically during the YD.

In western and eastern Africa, pollen records off Senegal (GeoB9508-5) and off Tanzania (GeoB12624-1) cover partly the period between c. 19 and 12 kyr BP, at centennial- to subcentennial-resolution, and provide new information on the deglacial vegetation of these regions, which shows contrasting vegetation changes. Using last deglaciation pollen records from the continental slope off Senegal, the data show that the Sahel drought remained severe during HS1 with maximum CCA representation along with elements from the savannah and semi-desert/desert vegetation, while Poaceae are represented before and after HS1. The marine pollen record off the Rufiji River shows low percentages of CCA during HS1 along with high percentages of tropical forest, savannah elements and mangrove as well as *Podocarpus* indicating less severe HS1 droughts in contrast to West Africa.

The Holocene records off northwest (NW) Africa (GeoB7920-2) and South Africa (GeoB8331-4) show similar trends with a clear dominance of three biomes, the semi-desert/desert vegetation and CCA, the Mediterranean forest, and fynbos. While the latter is rather constant
throughout the Holocene, the former shows a clear decrease in CCA and semi-desert/desert vegetation during the early Holocene followed by a remarkable increase after c. 5 kyr BP. Poaceae reach their maximum values between c. 10 and 6 kyr BP. The short record of GeoB8601-3 offshore Morocco shows a constant dominance of semi-desert/desert vegetation with a clear increase in Poaceae pollen during the last 1000 years.

### 22.4.2 Last glacial cycle

Eight sites, of which two sites from the eastern African margin have been selected for this time interval (Figure 3). In northern Africa, a record of maximum extension of the Mediterranean forest is found at the northernmost site off northern Morocco, GIK15669-1 at 34°N (Hooghiemstra et al. 1992) during the last glacial cycle, which is coincident with a similar forest expansion in Europe (e.g. Sánchez Goñi et al. 1999). The GIK15627-3 pollen record off southern Morocco at 29°N (Hooghiemstra et al. 1992) depicts a different pattern with a clear dominance of CCA and semi-desert/desert vegetation. Although lower than the previous record, a slight extent of the Mediterranean forest is observed for Marine Isotope Stage (MIS) 5 that continues until the present along with Poaceae that decrease however, rapidly after MIS5.

In equatorial Africa, the GIK16856-2 pollen record offshore Guinea at 5°N (Dupont and Weinelt 1996) shows an extension of mangrove forest during MIS5 and the last 20,000 years along with a minimum representation of Poaceae pollen reflecting moist continental conditions that coincide with interglacial and last deglacial conditions, respectively. *Podocarpus* percentages show maxima during the latter part of MIS5 indicating a well-developed Afromontane forest as a response to a cooler climate during the stadials MIS5b and MIS5d.

Further south, maximum expansion of the tropical forest is observed at the complete equatorial site GeoB1008-3 at 6°S offshore northern Angola (Jahns 1996). MIS 5 exhibit low Poaceae percentages while *Podocarpus* reach their highest values indicating a cooler climate during the stadials of MIS5. In contrast to the previous record, mangrove forest is less represented along with other biomes. The pollen record GeoB1016-3 off Southern Angola at 11°S (Shi and Dupont 1997) shows a contrasting pattern compared to the previous records. Here, we see a clear dominance of the semi-desert/desert vegetation along with Poaceae pollen except for MIS5 where tropical forest and to a lesser extent mangrove are well developed. *Podocarpus* is well developed during MIS5c-d and the last 10,000 years of the record. The record of GeoB1711-4 (Shi et al. 2001) from the Namib Desert shows a constant dominance of semi-desert/desert vegetation and Poaceae with the presence of CCA. However, a small but significant increase in tropical forest and *Podocarpus* pollen is observed during the stadials of MIS5 reflecting slightly cooler conditions.

In eastern Africa, the MD96-2048 pollen record from southern Mozambique at 26°S shows a clear shift from tropical forest dominance during MIS5 to semi-desert/desert vegetation and Mediterranean forest dominance afterwards (Dupont et al. 2011). In contrast, the GeoB9311-1 pollen record off the Zambezi catchment at 21°S (Dupont and Kuhlmann 2017) shows a co-dominance of tropical and temperate forests for the entire record. On the other hand, *Podocarpus* pollen is very well represented during MIS5 in the southern record while they do not exceed 20% in the northern record. This suggest that on a regional scale climatic perturbations of the vegetation cover in the Zambezi catchment are less severe than in southern Mozambique.

### 22.4.3 Mid-Pleistocene

Three pollen records were selected to assess glacial-interglacial fluctuations in the vegetation records around Africa during the Mid-Pleistocene (between c. 1.2 and 0.4 Million years (Myr) BP; Berger and Jansen 1994) (Figure 4A). In eastern Africa, the recently published pollen record off southern Mozambique MD96-2048 at 26°S (Dupont et al. 2019) represents a unique and continuous high-resolution African record from the Indian Ocean, to study the long-term
evolution of orbital-scale vegetation changes. The terrestrial pollen assemblages indicate that during glacials, specifically during MIS 7, 9, 11, and 17, the vegetation of eastern South Africa and southern Mozambique largely consisted of tropical forest vegetation indicating relatively wet conditions. During glacials, Mediterranean elements (here represented by the ericaceous vegetation in the mountains) along with semi-desert/desert elements dominated the pollen assemblage. *Podocarpus* pollen does not display variability related to glacials or interglacials.

In equatorial Africa, represented by the ODP1075 pollen record off Congo at 4°S (Dupont *et al.* 2001) and GIK16867-3 record off Gabon at 2°S (Dupont *et al.* 1998), vegetation is mainly dominated by tropical forest and mangrove. The tropical forest expands widely during interglacials (MIS 7, 9, 11, 13, 15, and 17) along with mangrove in sites offshore Gabon, while the semi-desert/desert vegetation slightly increases during the glacials. *Podocarpus* shows higher percentages during glacials indicating the expansion of mountainous forest during cold periods. The ODP1075 pollen record shows a much higher representation of mangrove forest along with tropical forest increasing strongly during periods of sea-level rise (Scourse *et al.* 2005). Poaceae show rather lower values during interglacials MIS17, 19, 21, and 25 while *Podocarpus* does not show a clear trend.

### 22.4.4 Plio-Miocene

Four records are presented here to reconstruct Miocene (c. 23 to 5.3 Myr BP) to Pliocene (c. 5.3 to 2.5 Myr BP) changes of African vegetation and rainfall regime (Figure 4B). In SW Africa, the South Atlantic ODP1085A pollen record at 29°S (Dupont *et al.* 2019) consists mainly of a strong representation of desert and semi-desert vegetation and Poaceae pollen implying that conditions were already arid 10 Myr ago. *Podocarpus* exhibit elevated relative abundances during the Miocene while it disappears quasi-completely during the Pliocene. Authors have inferred changes in the relative amount of precipitation and indicated a shift of the main moisture source from the Atlantic to the Indian Ocean during the onset of a major aridification 8 Myr ago (Dupont *et al.* 2013). The ODP1081A pollen record (Hötzel *et al.* 2015) offshore Namibia covering the time interval between 9 and 2.7 Myr BP consists mainly of pollen from semi-desert/desert vegetation. While, *Podocarpus* occurred during the Miocene, grasses expanded during the Pliocene.

In NW Africa, the Plio-Pleistocene pollen record ODP659A at 18°N (Vallé *et al.* 2017) shows more variability in the pollen content. After 3.5 Myr BP, the abrupt increase of CCA and Poaceae suggests larger climate variability during that interval implying continent-wide aridity during eccentricity maxima between 3.2 and 2.5 Myr BP. From 2.5 Myr BP on, the trend in ODP Site 659 is characterized by a slight increase of Mediterranean forest and semi-desert/desert vegetation and a clear decrease in Poaceae pollen. *Podocarpus* pollen are present during the Pliocene with very low relative abundances but quasi-absent during the early Pleistocene. The ODP658 pollen record off Cap Blanc at 20°N (Leroy and Dupont 1994) shows a similar trend as ODP659 during the late Pliocene. However, Poaceae pollen that reach up to 59% during the Late Pliocene continue to be well represented through the early Pleistocene. *Podocarpus*, similarly to the ODP site 659, is present with very low percentages during the late Pliocene and between 1.7 and 2 Myr BP.

## 22.5 POLLEN-CLIMATE RELATIONSHIP IN AFRICA

Today, Africa is mainly dominated by open landscapes between 30°S and 30°N with the exception of the Mediterranean, equatorial and mangrove forests and the afromontane forests. These open landscapes range from desert, dry forests, to woodlands, wooded grasslands, grasslands, and fynbos (White 1983). Transitions between forest, savannah and desert vegetation types as well as Mediterranean forest in African fossil pollen records are often poorly understood due
to the scarcity of modern pollen-vegetation studies (Julier *et al.* 2018; Lézine and Hooghiemstra, 1990; Vincens *et al.* 2000) and the over-representation/under-representation of certain taxa. Shifts in biome distributions imply significant changes in climate, especially the precipitation gradient throughout several time scales, reflecting a change in monsoon extent combined with a southward expansion of the ITCZ (Shanahan *et al.* 2015). Outside the influence of the monsoon, westerly storm tracks bring rainfall to the northernmost and southernmost parts of Africa (Jolly *et al.* 1998). Additionally, biomes are differently represented, because the biome characteristic taxa have very different pollen production rates with different pollination strategies (entomophily (insects); lepidopterophily (butterflies); anemophily (wind); chiropterophily (bats); and ornithophily (birds)), and different dispersal mechanisms. Forest taxa which are frequently entomophilous are under-represented (Vincens *et al.* 2000), while anemophilous taxa such as Poaceae are generally over-represented relative to their abundance in the vegetation (Bush and Rivera 1998). Pollen of Combretaceae and *Alchornea* are better represented in the marine sediments than other trees due to the better pollen dispersal compared to many other tropical forest trees (Dupont 2011; Watrin *et al.* 2007). Although, the relative abundances of pollen grains cannot be simply translated into vegetation composition, it could be interpreted as relative changes of biomes through time. In marine sediments, this issue becomes even more serious as fossil pollen records effectively show only a part of the vegetation on the adjacent continent. The reduced representation of the assemblage is less in pollen data from terrestrial deposits, which give more local information. However, due to the relatively good preservation of pollen grains in certain marine records, good age control and coverage of long periods, marine archives allow us to study vegetation changes over several continuous climate cycles. Here, we present distribution maps of arboreal pollen percentages (AP%) from available marine pollen records off African shores for different time-slices (Figure 5) in order to discuss changes in regional vegetation and environmental conditions over orbital and glacial-interglacial timescales and to assess the low-to mid-latitude interhemispheric climatic implications and mechanisms.

## 22.6 PATTERN OF LANDSCAPE CHANGES

We show four arboreal taxa categories (AP%), as also used by Lézine *et al.* (this issue), to characterize the African landscapes through several climate cycles (Figure 5): (i) AP higher than 45% corresponding to more or less closed canopy, (ii) $15<AP<45\%$ intermediate between closed canopy and open landscapes, (iii) AP lower than 15% indicating grass-dominated landscapes, and (iv) AP%=0.

During the early Holocene, marine pollen records show high percentages (AP>$45\%$) of arboreal taxa in most of Africa. Exceptions are found offshore of SW Africa (South Africa and Namibia), Gulf of Aden and Mauritania. This indicates the prevalence of forested vegetation types over tropical and Mediterranean Africa linked to humid conditions. Late Holocene records show a more open landscape as many sites contain lower relative abundances of arboreal taxa (AP<$15\%$) reflecting grass dominated landscape, thus drier conditions than in the early Holocene.

Between 21 and 11.8 kyr BP, last deglaciation marine pollen records show a more open vegetation with widespread grassland, as well as savannah and xerophytic scrubland vegetation (Figure 2) indicating dry climate especially during the last glacial maximum (LGM). AP% are higher (>45%) in Equatorial Africa and in NW and SE Africa even during HS1 and LGM whereas the rest of the marine African pollen records are characterized by a strong representation of grasses.

Between 50 and 21 kyr BP, open grasslands and savannahs dominate NW and SW Africa, the tropical regions and SE Africa show a mixture between closed canopy and open landscapes, while equatorial Africa is characterized by a more or less dense vegetation during HS2 and HS3. In general, HS4 and HS5 display intermediate AP% ($15<AP<45\%$) indicating relatively wetter conditions.
Between 80 and 50 kyr BP, pollen records show that HS6 is characterized by a return to a more open vegetation and thus, drier conditions in NW Africa and Gulf of Guinea compared to the previous HS. HS7 and HS8 exhibit similar trends as HS4 and HS5 with particularly higher AP% (>45%) during HS8 in SE Africa. Taken together the AP% distributions over the last 80,000 years show, to a certain extent, a north-south rainfall gradient consisting of lower AP% (<15%) in NW and SW Africa, intermediate AP% in tropical Africa and SE Africa and higher AP% in equatorial Africa. Although marine pollen records from eastern Africa are extremely understudied compared to western Africa, we could observe a contrast between the relatively denser SE and the open SW African landscape; forests only occurred in western equatorial Africa between 2°N and 12°S. The AP% distribution maps show that the intervals spanning the LGM, HS1 HS2 and HS6 are marked by an increase in open vegetation, mainly savannah and xerophytic vegetation as shown in Figure 5. These changes occur mainly in NW and SW Africa indicating that major changes in biome distributions occurred north of 10°N and to a certain extent south of 20°S.

### 22.6.1 Interglacials vs. glacials

For MIS5, one of the best studied warm stages in Africa represented by 21 records, open landscapes dominate the Sahel/Sahara region from 20° to 30°N and SW Africa and decline in 12 sites located in western equatorial Africa, north and SE Africa where intermediate and higher AP% are more prominent. This indicates a relatively wetter climate during MIS5 compared to the previous period. During MIS6 (represented by 19 records), open landscapes dominate the coast between 30°N and 9°N indicating a southward shift of the savannah biome during this glacial period. MIS7 (represented by nine records) shows a clear dominance of arboreal taxa except one site offshore Morocco indicating a return to wetter conditions. The next time slices, which are represented with only few sites each (average of 3 to 5 records) seem to follow the pattern of odd- and even-numbered MIS and show an alternation between dense arboreal dominance during MIS9, 11, 13, 15, 17, 19, 21, 25, 31, and 37 and more open vegetation during MIS 10, 12, 14, 16, 18, 20, 24, and 32, especially in NW and SW Africa.

MIS20 and MIS26 form an exception showing higher arboreal pollen percentages offshore of the Sahara. Moreover, the eastern African site that exhibited intermediate to higher arboreal taxa values throughout all timescales indicated an open-dominated landscape during MIS32 reflecting dry conditions in this area compared to previous climate cycles. The only few available records representing the Pliocene and the Miocene show mostly grass-dominated landscapes and dry forests.

Taken together, the AP% distribution maps show that dense forests and intermediate tree cover were able to persist in equatorial and eastern Africa through all marine isotope stages shown in Figure 5 (except MIS32). The scarcity of eastern African marine sites, however, hampers a reliable comparison in order to understand the response of the eastern African biomes to climate variability in this climatically highly complex region.

### 22.6.2 Low vs. mid-latitudinal variability

The influence of obliquity, the tilt of the Earth's rotational axis, on incoming solar radiation at low latitudes is small, yet many tropical and subtropical palaeoclimate records reveal a clear obliquity signal (Dupont 2011; Dupont et al. 1989). This is particularly important since in terms of mean energy balance the integrated summer insolation is more important than maximum insolation, which is influenced by obliquity and not by precession (Huybers 2011). Additionally, the insolation gradient between high and low-latitudes depending on obliquity controls the atmospheric meridional flux of heat, moisture, and latent energy (Raymo and Nisancioglu 2003). Obliquity's control on meridional insolation gradients weaken, or strengthen, the mid-latitude westerlies and the subtropical trade winds (Lee and Poulsen 2005). Yet, model simulations suggest that
the c. 100 kyr cycle signal was not a robust feature of tropical vegetation, which is subject to stronger direct forcing by the precessional (c. 21 kyr) orbital cycle (Gosling and Holden 2011). However, Dupont (2011) has shown significant power around 100 kyr at all records she has analysed in her review paper, which is interpreted as an effect of glacial boundary conditions. Thus, the correlation of palaeoenvironmental changes from African pollen records with global temperature change remains ambiguous and must be done with great caution. The AP% distribution maps (Figure 5) and pollen diagrams (Figure 2) indicate that during the Holocene, YD and HS1, the response of arboreal vegetation reversed at subtropical latitudes between hemispheres, whereby NW African sites exhibit higher AP% than those of SW Africa. Arboreal taxa values show maxima at equatorial and tropical sites from the northern and southern hemispheres during warm stages (Figure 5) and a clear reduction during cold stages (Figures 3 and 4A) probably driven by summer insolation, which is expected to be the main forcing mechanism of rain forest variability. Summarizing the marine palynological results covering several glacial-interglacial climate cycles, it is suggested that the equatorial rain forest extent in tropical Africa varies with summer insolation; with boreal summer insolation in the northern part and with austral summer insolation in the southern part.

## 22.7 PERSPECTIVES

This paper attempts to review and synthetize all available marine fossil pollen records from offshore marine cores around the African continent to explore the vegetation response to climate changes in millennial- and orbital-timescales. There is a clear need for more and higher resolution records especially from the eastern African shores. There is also a need to improve dating of the key records and create age models. Marine pollen records may be difficult to interpret as they record an integrated mixture of pollen coming from large source areas. Nevertheless, if the dispersal and transport mechanisms as well as the diagenesis and preservation are taken into account, they can be very useful to document latitudinal shifts in biomes and to complement the existing information from terrestrial records. This review was possible thanks to the available data sets of pollen records submitted to different databases and to personal communications with some authors. However, there is still a big amount of missing data that have not been submitted in any database although the corresponding articles have been recently published. Therefore, there is an urgent need to encourage colleagues all over the world to make their data public for the general scientific interest.

## 22.8 CONCLUSIONS

Palynological approaches are moderately useful in distal offshore ocean settings characterized by oligotrophic conditions because of low concentration of palynomorphs, making it difficult to do statistically representative counts. On the other hand, combined with the fundamental problems of tropical palynology (the under-representation of many species in the pollen record), the pollen grains found in marine sediments are typically transported over long distances, through winds and water, making it difficult to identify the precise source area. However, one of the main advantages of pollen records from marine sediment sequences is that they provide access to exceptionally long palaeoecological records that are crucial to understand the vegetation response to climate forcing over time and allow direct correlations of climate change over land and in the ocean, with minimal chronological uncertainty. Marine pollen records offer a unique opportunity to associate continental environmental changes with marine environmental changes inferred from the study of other palynomorphs (dinoflagellate cysts) or other sedimentary, geochemical or micropalaeontological proxies.
The overview presented here has shown that African vegetation and climate responded to long-term and shorter-term climate changes. There was a dynamic equilibrium between vegetation and climate for short periods of forcing such as the Holocene and HEs. Within the Interglacials (especially MIS5e), the African margin shows a clear dominance of arboreal taxa in most sites (with some exceptions) indicating moist conditions. A different trend has been observed between low- and mid-latitudes. The forest expansion shows maxima during interglacials and a clear reduction during glacials at equatorial and tropical sites from the African northern and southern hemispheres.

This overview has also shown that the western coast of Africa is well documented with continuous pollen records dating back to the Miocene thanks to the commitment of some researchers over the last few decades. The atmospheric circulation conditions that favour pollen transport towards the ocean, the latitudinal distribution of the major biomes as well as the reconstruction of regional vegetation and its response to climate changes are one of the most important outcomes of this research. However, the eastern coast of Africa, a climatically highly complex region, is poorly documented. With the exception of few sites at the mouths of large rivers such as Limpopo, Zambezi and Rufiji, marine pollen records are rare in this part of Africa but extremely important to understand the response of the ecosystems to climate variability. More marine pollen records are therefore, necessary to provide independent evidence into the timing of vegetation changes in a regional context and their connection to global climate. Moreover, they would offer an important complement to previously published palaeorecords from continental archives such as the Great Rift Lakes (Tanganyika, Malawi, Victoria).

## ACKNOWLEDGEMENTS

The authors wish to express their gratitude to all African Pollen Database (APD) contributors and colleagues who made their data available for this study and for the excellent discussions during the APD meeting in Bondy. We thank Henry Hooghiemstra and William D. Gosling for their constructive comments on the manuscript. IB, HR, AB are funded by the German Federal Ministry of Education and Research (BMBF), through the PMARS III grant (PMARS2015-100)". LD by the University of Bremen, and AML by CNRS.

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# Inside-of-Africa: How landscape openness shaped *Homo sapiens* evolution by facilitating dispersal and gene-flow in Middle and Late Pleistocene Africa

Mick N.T. Bönnen, William D. Gosling & Henry Hooghiemstra

*Institute for Biodiversity and Ecosystems Dynamics, University of Amsterdam, Amsterdam, The Netherlands*

ABSTRACT: *Homo sapiens* as a clade originated c. 500 thousand years before present (500 ka) as it diverged from *Homo neanderthalensis*. The topic of early *H. sapiens* evolution and dispersal since this cladogenesis has long been of interest in scientific literature and public debate. The development of this field has been significantly accelerated in recent years by the advances made in the scientific fields of archaeological, anthropological and genetic research; exemplified by the publication of the earliest observed fossil belonging to the archaic *H. sapiens* clade at Jebel Irhoud, Morocco, dated at c. 315 ka in 2017. Recent evidence from these fields opposes the long-held view that anatomically modern humans (AMH) evolved linearly from a single population. Instead, a pan-African model of evolution is proposed, whereby geographically isolated *H. sapiens* populations, possibly shaped and maintained by ecological boundaries, evolved independently with fluctuating degrees of gene-flow over time. A thorough understanding of the ecological context these hominins experienced has long been hampered by spatial and temporal gaps in the African palaeovegetation record. Records of past vegetation that cover timescales relevant to the emergence of AMHs now exist that are relevant to environmental change in northen, southern, eastern, western and central Africa. This means it is becoming possible to explore how hominin evolutionary development coincided with the changing vegetational (habitat) context. We present the idea of a three-stage 'Inside-of-Africa' environmental framework for hominin evolution: (i) a predominance of hospitable vegetation 500-400 ka facilitating initial dispersal of archaic *H. sapiens*, (ii) a predominance of ecological barriers (e.g. deserts and rainforests) 400-250 ka limiting dispersal and gene-flow, causing independent evolution, and (iii) a predominance of hospitable vegetation 250-100 ka (re-)connecting populations and resulting in the combination of the full suite of contemporary AMH characteristics. To test this framework we review and synthesize all available long (>c. 100 ka) lacustrine palynological records relevant to past vegetation change across Africa. We find the past vegetation data supports the waxing and waning of hospitable vegetation and ecological barriers during the last 500 ka in line with the timings proposed in our environmental framework.
## 23.1 INTRODUCTION

### 23.1.1 Archaic *Homo sapiens*

Africa is regarded as the cradle of our own species (Mounier and Mirazón Lahr 2016) because it is where the archaic *Homo sapiens* clade diverged from the *H. heidelbergensis* c. 700-400 thousands of years before present (ka) (Stringer 2016), and where we shared our last common ancestor with *H. neanderthalensis* c. 440-410 ka (Endicott *et al.* 2010) (Figure 1). Although the exact location of cladogenesis remains unknown, these archaic forms of *H. sapiens* radiated all over Africa. Currently, the earliest ‘archaic’ manifestations of the *H. sapiens* clade are found in Jebel Irhoud, Morocco, comprising of cranial fossils dated to be about 315 ka (Hublin *et al.* 2017; Richter *et al.* 2017). Later dated archaic *H. sapiens* remains include fossils from Florisbad in South Africa (c. 260 ka) (Grun *et al.* 1996) and Omo Kibish and Herto, both Ethiopia, which have estimated ages of c. 195 and c. 160 ka respectively (McDougall *et al.* 2005; White *et al.* 2003). Even though all these archaic humans belong to the *H. sapiens* clade, and share a fairly recent last common ancestor, their fossilized remains show distinct spatial and temporal morphological variation when compared with each other, and with anatomically modern humans (AMH; Gunz *et al.* 2009).

The pan-African spread of hominins, in conjunction with the array of morphological variation (Hammond *et al.* 2017; Lieberman *et al.* 2002; Neubauer *et al.* 2018; Pearson 2008), has lead the modern scientific discourse to consider a mosaic-like pattern for the evolution of modern human traits (Gunz *et al.* 2009; Serri *et al.*, 2017a; Stringer 2016). A mosaic-like pan-African pattern could have been created if populations became (semi-)isolated for millennia by distance and/or ecological barriers (such as deserts or dense rainforests). The consequence could be that specific modern human traits might have evolved independently in different regions and became combined later when populations reconnected. The amalgamation of our modern characteristics could have therefore potentially been strongly mediated by past environmental changes. For example, periods of increased landscape connectivity between hominin populations, brought about by an increasing predominance of open vegetation, could have facilitated gene flow between small semi-isolated populations across Africa (Bertola *et al.* 2016). Recent genetic studies have suggested that between c. 250-100 ka most extant lineages emerged (Lipson *et al.* 2020). The eventual admixture of individual traits associated with these populations led to the homogenization of the human phenotype, thereby refuting the notion that our lineage can be traced back to one specific region, but favouring a pan-African view of *H. sapiens* evolution instead. Analyses of whole-genome sequences of contemporary African populations provide a time-dependent estimate of gene flow that suggests a pattern of population separation, followed by isolation, and then subsequent recombination (Wang *et al.* 2020).

Similar to morphological characteristics, spatiotemporal diversifications since our last common ancestor with *H. neanderthalensis* are also reflected in behavioural practices such as material cultures. An abandonment of large and crude cutting tools (e.g. hand axes) in favour of more sophisticated techniques for tool-carving ('prepared-core' technologies) occurred almost simultaneously on a pan-African scale. These innovations in stone tool technology followed a long period of stasis (the Early Stone Age [ESA] c. 3 Myr to 200 kyr BP) and mark the start of the Middle Stone Age (MSA) period (c. 280-20 kyr BP, Galway-Witham *et al.* 2019). The MSA is also when regionally distinctive material cultures involving complex stone tools first become apparent in the archaeological records. For example during the MSA features such as tangled implements (securing stone tools into wooden hafts) emerged in northern African populations (Serri 2017b), central African materialistic culture started to be characterized by distinctive
<figure><img src="image_124.png" /></figure>

**Figure 1.** 'Inside-of-Africa' conceptual environmental framework related to the evolution and development of hominins. Vegetation openness relates to the proportion of open (savannah) or closed (forest) vegetation on the continent. General characteristics of vegetation for each period are indicated by (I) open and hospitable to hominins, (II) closed with more environmental barriers to hominins, and (III) open and hospitable for hominins. AMH = Anatomically Modern Humans. Out-of-Africa = the period of human dispersal from the African continent (IV). Key archaeological sites yielding *H. sapiens* fossils indicated are Jebel Irhoud, Morocco (Hublin *et al.* 2017), Florisbad, South Africa (Grun *et al.* 1996), Omo Kibish, Ethiopia (McDougall *et al.* 2005), and Herto, Ethiopia (White *et al.* 2003).

stone tools (Scerri 2017a), while southern African cultural artifacts started to include complex material aspects; such as the use of ochre, bone tools and shell beads (D'Errico et al. 2017).

### 23.1.2 Hypothesis development

In this review, we focus on how changing environments could have shaped hominin evolution inside Africa. Building on the literature, we propose here a new framework for understanding this interplay between archaic *H. sapiens* and their contemporary landscapes. Our 'Inside-of-Africa' framework includes alternating periods of environmental hospitability and ecological barriers that either limit or encourage dispersal (Figure 1):

I. Initial dispersal of archaic *H. sapiens* across Africa (c. 500-400 ka) was facilitated by increased landscape openness, which made areas generally more hospitable (hereafter defined as landscapes not dominated by dense (rain)forests or deserts, but rather by open ecosystem mosaics, including: wooded) grasslands, savannahs, and gallery forests).

II. Intraspecific variation was promoted and cultural development fragmented between (c. 400-250 ka) by a rise in the number of environmental barriers (e.g. arid deserts and impenetrable forests), which (semi-)isolated *H. sapiens* populations to environmentally constrained hospitable regions (refugia).

III. The (re-)combination of traits into the full suite of AMH characteristics (c. 250-100 ka) was facilitated by increased landscape openness.

This review collates lacustrine palynological records with a pan-African spatial coverage from the period relevant to hominin evolution as outlined above (Figure 1). These data assess the current state of available information on past vegetation from terrestrial sites. We use the synthesized past vegetation information to test ideas on the evolution, development and dispersal of hominins. Specifically, we classify the long palynological records as indicative of relatively more open, or closed, vegetation structure (grasslands to dense forests) and identify any directional vegetation trends coincident with hominin evolution.
## 23.2 AFRICAN ENVIRONMENTS DURING THE MIDDLE AND UPPER PLEISTOCENE

### 23.2.1 Current ecosystems

The wide range in topography and climatic conditions across Africa caused varied landscapes that are home to a plethora of ecosystems (Dupont 2011; White 1983). Following Dupont's (2011) simplified version of the African vegetation classifications made by White (1983), we can distinguish between eleven different biomes in contemporary Africa (Figure 2A).

The continent's most northern and south-western extent is typified by arid biomes. Generally speaking, we find Mediterranean forests along the north-African coast from Morocco to Egypt adjoining the Mediterranean Sea, while Africa's most southern tip, the southern-African coasts and Cape Fold Mountains, are dominated by fynbos vegetation. Mediterranean forests have a significant presence of arboreal species; typically oak (*Quercus*) and maple (*Acer*) in broadleaved forests, while pine (*Pinus*) and yew (*Taxus*) dominate the coniferous forests. The fynbos vegetation on the other hand has a low density of arboreal taxa, as it is mostly dominated by shrubby vegetation like Ericaceae. Further inland deserts occur. In the north, the Sahara (best-represented families being Asteraceae, Leguminosae and Poaceae (Ozenda 1991)) stretches from the Red Sea to the Atlantic. In the south the Namib desert covers the entire Namibian coast and parts of the Angolan and southern African coast. The transition between the Mediterranean forests and the Sahara, the Sahel region, the African Horn, and the area of the fynbos-to-desert transition in the south (the Kalahari desert) are classified as semi-deserts, where we find low densities of shrubby vegetation like Asteraceae. Poaceae-dominated systems are found throughout Africa. Grass savannahs are ubiquitous at the 15°N and the 20°S latitudes and in east African Rift Valley system. Edaphic grasslands (those controlled by soil conditions instead of climate, fire regimes,

<figure><img src="image_125.png" /><figcaption>**Figure 2.** (A) Modern African vegetation simplified from Dupont (2011). (B) Location of the seven pollen records obtained from lake settings relevant to past vegetation change in Africa relevant to hominin evolution over the last 500 thousand years. PB = Padul Basin, Spain (Torres *et al.* 2020), VVV10.1 = Vankervelsvlei, South Africa (Quick *et al.* 2016), MAG14 = Lake Magadi, Kenya (Owen *et al.* 2018), MAL05-1B/1C (MAL05-1B and MAL05-1C) = Lake Malawi, Malawi (Beuning *et al.* 2011; Ivory *et al.* 2018), B12 = Lake Bambili, Cameroon (Lézine *et al.* 2019), and BOS04-5B = Lake Bosumtwi, Ghana (Miller and Gosling 2014). Marine cores presented for additional context are ODP-658 (Dupont 1989; Dupont and Hooghiemstra 1989) and ODP-659 (Tiedeman *et al.* 1994).</figcaption></figure>
or herbivory) can be found in Angola, Zambia and the Democratic Republic of Congo. Montane grasslands are prevalent in the arid high-altitude regions of central Africa, the East-African Highlands and the South-African Highveld. Forested areas are restricted to the moist equatorial regions and the high elevation Afromontane forests found in East-Africa and South Africa. Tropical rainforests extend across the basin of the Congo River and its tributaries but are also found along the coast of western Africa, spreading from southern Guinea all the way east to southern Cameroon. At higher latitudes tropical moist forests transitions into deciduous forests/woodlands as the vegetation becomes increasingly influenced by seasonality in precipitation.

To understand how vegetation association, and thus potential habitats or barriers for early *H. sapiens*, varied over time it is important to understand the climatic factors that relate to vegetation formation and how this has changed. Orbital precession, with a c. 21,000 year cycle, has a strong influence on long-term climate change in the low elevation tropics (Clement *et al.* 2004). Precession directly affects when in the year the earth is closest to the sun, and thus governs the amount of insolation received during each season. The strength and the annual latitudinal reach of the tropical rain belts are governed by changes in insolation that consequently are directly influenced by changes in the precessional cycle. Specifically, at the peak in the precessional cycle, the monsoons can reach further northwards into the otherwise arid part of Africa (Dupont and Hooghiemstra 1989; Frumkin *et al.* 2011). This additional moisture delivery has a significant impact on vegetation cover, and climate-vegetation simulations suggest that this processional climate signal is a dominant control on vegetation change at low latitudes (Gosling and Holden 2011).

### 23.2.2 Ecological boundaries and refugia for archaic *Homo sapiens*

Environmental changes, prompted by changes in precipitation related to multi-millennial-scale climate oscillations have been shown to shape and maintain ecological boundaries that eventually limited gene-flow between populations in lions (*Panthera leo*), thereby creating distinct genetic clades (Bertola *et al.* 2016). Similar biogeographic patterns of speciation seem to exist in a wide array of African mammals (list of references in Bertola *et al.* 2016), and the same mechanism has been postulated for archaic *H. sapiens* populations (Scerri *et al.* 2018). Habitats largely inhospitable to archaic *H. sapiens*, such as arid deserts and dense rainforests (Bailey *et al.* 1989; Blome *et al.* 2012; Coulthard *et al.* 2013), expanded and retracted over time-scales of millennia in response to orbital scale vegetation change (Dupont 2011). The expansion of deserts and rainforests often occurred at the expense of open ecosystems (e.g. savannahs) which are thought to have been the preferred habitat of early hominins based on the close affinity between archaeological evidence of hominins and grasslands ecosystems (Cerling *et al.* 2011; Larrasoña *et al.* 2013). It can therefore be hypothesized that climatic conditions that caused a decline in savannah ecosystems in favour of deserts and rainforests would have caused a loss of habitat for archaic *H. sapiens*. This loss of hospitable environment could have lead to the migration of some *H. sapiens* populations and a loss in connectivity between others and thus generated the population structure needed for independent evolution. As the remaining hominin populations became more isolated they likley retreated to 'refugia' (isolated regions where environmental conditions allowed humans to persevere amidst inhospitable conditions (Mirazón Lahr and Foley 2016)) which have also been highlighted as catalysts for evolutionary change in *H. sapiens* (Stewart and Stringer 2012).

### 23.2.3 Palaeoenvironmental reconstructions

Marine palynological records have been used to provide a pan-African view of vegetation change (Dupont 2011). The advantage of marine records is that they are well-dated and yield the ability to record large scale vegetation change from a wide source area (Castañeda *et al.* 2016; Dalibard
et al. 2014; Hooghiemstra et al. 2006; Jahns et al. 1998; Zhao et al. 2003). However, interpretation of past vegetation cover from marine pollen records is challenging (Frédoux 1994; Hooghiemstra et al. 1986) because of the inherent wide pollen source area, which means that the signal is influenced by: (i) the intricate complexity of wind current and fluvial dynamics that muddle the opportunity to precisely identify the source (Dupont et al. 2000), and (ii) a low spatial resolution that makes it impossible to see vegetation dynamics on a local scale. For example in regions dominated by arid vegetation but where lush vegetation boarders rivers, the marine pollen signal could be biased towards the lush vegetation as it produces relatively more pollen and they are easily transported into the ocean sediments. In contrast to the marine records, the pollen found within a lake (diameter 5–20 km) likely reflects local/extra-local (10–100 s m) and regional (1–10 s km) vegetation (Jacobson and Bradshaw 1981). Therefore, lacustrine pollen records are more suitable to reconstruct vegetation changes at the local and regional scales, which allows the habitats of archaic *H. sapiens* to be investigated.

## 23.3 SITE SELECTION

To provide the vegetational context in which early *H. sapiens* evolution took place we selected palaeovegetation records that contain information relevant from across Africa. The most appropriate records were chosen to represent each of five African regions (northern, southern, eastern, western and central) based on two criteria:

* Sedimentary record covering at least the last c. 100 ka.

* At least one proxy of past vegetation change has been published from the record.

Six lacustrine records were identified meeting these criteria from in, and around, the African continent (Table 1; Figure 2B).

## 23.4 LONG-TERM VEGETATION CHANGES IN AFRICA

One record of past vegetation was obtained from each region, except for eastern Africa, from which two were obtained (Figure 3). The records ranged from c. 90 ka to 800 ka in duration and past vegetation information was obtained from fossil pollen at all sites. To place these records in the context of global climatic change we refer to the global glacial (cool) and interglacial (warm) Marine Isotope Stages (MIS) as defined by Imbrie *et al.* (1984). The six records are now reviewed in turn, in the order of the earliest archaeological evidence of *H. sapiens* in the vicinity of the core site: (i) Padul Basin, northern Africa region (Torres *et al.* 2020), (ii) Vankervelsvlei, southern Africa region (Quick *et al.* 2016), (iii) Lake Magadi, eastern Africa region (Owen *et al.* 2018), (iv and v) Lake Malawi, eastern Africa (Beuning *et al.* 2011; Ivory *et al.* 2018), (vi) Lake Bambili, central Africa (Lézine *et al.* 2019), and (vii) Lake Bosumtwi, western Africa (Miller and Gosling 2014).

### 23.4.1 Padul Basin, Spain

No lacustrine sedimentary record spanning c. 100 kyr has, to date, been recovered or analysed for pollen from continental north-west Africa. Therefore, the sediment record from the Padul Basin (PB) from the Granada province in south-east Spain (Torres *et al.* 2020) was chosen to provide the closest available vegetational context for the earliest known *H. sapiens* found to date (Figure 3A). The archaic *H. sapiens* fossils found at Jebel Irhoud (Morocco) have been dated to 315 ± 34 ka and include facial bones (Hublin *et al.* 2017). The PB sediment core was retrieved from a peat bog inside a closed flat depression, with a catchment area of 44 km², located 720 m
<table><caption>**Table 1.** List of selected lacustrine pollen records and metadata.</caption><thead><tr><th>Region</th><th>Site name</th><th>Core name</th><th>Country</th><th>Latitude<br>Longitude</th><th>Core<br>length<br>(m)</th><th>Dating<br>method</th><th># age<br>samples</th><th>Timescale<br>(ka)</th><th>Referenc</th><th>Earliest<br>human<br>evidence<br>(ka)</th></tr></thead><tbody><tr><td rowspan="2">Northern Africa</td><td>Padul Basin</td><td>PB</td><td>Spain</td><td>37°01'01"N<br>3°36'07"W</td><td>107</td><td><sup>14</sup>C/U/Th/<br>palaeomag</td><td>27</td><td>800</td><td>Torres et al.<br>(2020)</td><td>315</td></tr><tr><td>Vankervelsvlei</td><td>VVV10.1</td><td>South Africa</td><td>34°044.58"S<br>22°54'15.06"E</td><td>4</td><td><sup>14</sup>C/Luminescence</td><td>6</td><td>110</td><td>Quick et al.<br>(2016)</td><td>260</td></tr><tr><td rowspan="2">Eastern Africa</td><td>Lake Magadi</td><td>MAG14</td><td>Kenya</td><td>1°54'3.56"S<br>36°14'48.52"E</td><td>194</td><td><sup>14</sup>C/Ar-Ar/<br>U-series</td><td>18</td><td>1000</td><td>Owen et al.<br>(2018)</td><td>195</td></tr><tr><td>Lake Malawi</td><td>MAL05-1C</td><td>Malawi</td><td>11°17'37"S,<br>34°26'04"E</td><td>90</td><td><sup>14</sup>C/Luminescence</td><td>25</td><td>135</td><td>Beuning<br>et al.<br>(2011)</td><td>—</td></tr><tr><td rowspan="2">Eastern Africa</td><td>Lake Malawi</td><td>MAL05-1B/1C</td><td>Malawi</td><td>11°17'37"S,<br>34°26'04"E</td><td>170</td><td><sup>14</sup>C/palaeomag/<br>Ar-Ar</td><td>41</td><td>600</td><td>Ivory et al.<br>(2018)</td><td>—</td></tr><tr><td>Lake Bambili</td><td>B12</td><td>Cameroon</td><td>6°0'19.56"N<br>10°15'46.14"E</td><td>26.6</td><td><sup>14</sup>C</td><td>29</td><td>90</td><td>Lézine et al.<br>(2019)</td><td>30</td></tr><tr><td>Western Africa</td><td>Lake Bosumtwi</td><td>BOS04-5B</td><td>Ghana</td><td>6°30'6.04"N<br>1°24'52.14"W</td><td>295</td><td><sup>14</sup>C/Luminescence/<br>U-series/Ar-Ar</td><td>135</td><td>1000</td><td>Miller and<br>Gosling<br>(2014)</td><td>12</td></tr></tbody></table>
<figure><img src="image_126.png" /></figure>

**Figure 3.** Regional topographic context (main panels) and continental geographic contexts (inset panels) of lacustrine records reviewed in this study. (A) Padul Basin (Spain). (B) Vankervelsvlei (South Africa). (C) Lake Magadi (Kenya). (D) Lake Malawi (Malawi). (E) Lake Bambili (Cameroon). (F) Lake Bosumtwi (Ghana).
above sea level (m asl), and enclosed by mountains to the west (Albuñuelas range) and east (the Sierra Nevada). The altitudinal range of the mountains around the Padul Basin provides habitat for a wide variety of vegetation; from evergreen oak groves below 700 m to pine forests at the higher elevations (Rivas-Martínez 1987). Importantly, even though PB and Jebel Irhoud are located *c.* 750 km apart, they still encompass the same temperate Mediterranean Köppen climate area (Chen and Chen 2013; Rubel and Kottek 2010).

*Pinus* dominates the pollen record from PB during MIS 13.13 (c. 500 ka), making up c. 60% of the pollen spectra while the presence of Poaceae is low and accounts for only 10%. *Pinus* and Poaceae start to diminish between MIS 13.11 and 12.1 (480-425 ka) as mesophilic taxa (*Acer*, *Alnus*, *Quercus*, *Corylus*, *Carpinus*, *Fraxinus*, *Ulmus*) and riparian taxa (*Cornus*, *Populus*, *Salix*) become more abundant. Subsequently, a period of low pollen preservation is found until the start of MIS 11.2 (385 ka), which ends with a pollen assemblage dominated by *Pinus* that, in turn, transitions into a steppic vegetation (*Artemisia*, *Ephedra*) over a c. 45 kyr period. The transition to steppic vegetation is not smooth, with a peak in *Pinus* (70%) around the end of MIS 11 (360 ka), followed by a rapid decline to c. 10% at the start of MIS 10.2 (341 ka). Poaceae has a low presence throughout this transitional period, averaging c. 10%. Between MIS 10.2 and MIS 9.1 (341-310 kyr BP), the pollen assemblage is relatively diverse. Throughout this period Poaceae declines from c. 40% c. 310 ka to c. 10%, while *Pinus*, steppic taxa and Amaranthaceae all see a marked rise. From the start of MIS 8.5 (287 ka) Poaceae rises to its maximum abundance (c. 80%) in the entire record and *Pinus*, the most prominent taxon throughout the palynological record, is reduced to c. 5%. The dominance of the pollen assemblage by Poaceae continues for c. 5 kyr and then recedes back to c. 10% by 280 ka. From 280 ka until 170 ka Poaceae is c. 10%, and *Pinus* is c. 40%, while *Quercus* is most abundant between MIS 7.5-6.6 (238-183 ka). These episodes between MIS 7.5 and 6.6 (238-183 ka) are also characterized by a growing presence of steppic taxa, especially within the timeframe where *Pinus* percentages show lower values. Between c. 183 ka and c. 170 ka there is a hiatus in the pollen record. Pollen is recorded again halfway through MIS 6 (c. 170 ka), starting with a high abundance of *Pinus* (c. 80%) that declines to 30% at 130 ka, with steppic taxa and Poaceae present throughout. Steppic taxa and Poaceae then practically disappear from the record during MIS 5 (122-71 ka), but *Pinus* rises again reaching c. 80% at 120 ka. *Pinus* percentages keep on fluctuating around 50% for the remainder of the record up until the present, and the distinct changes in the vegetational compositions are due to fluctuations in pollen percentages of other taxa. The shrubby xerophilous taxa show a stable representation of c. 15% during the MIS 4-2 interval (65-12 ka), after which their presence disappears. Similar trends can be found in the steppic taxa, which also steadily increase up to 40%. When steppic taxa disappear Poaceae shows another peak, contributing close to 50% to the pollen sum; however, Poaceae, xerophilous (Amaranthaceae) and steppic (*Artemisia*, *Ephedra*) taxa are no longer represented towards the end of PB record.

### 23.4.2 Vankervelsvlei, South Africa

The sediment core recovered from Vankervelsvlei wetlands (34°0′44.58″S, 22°54′15.06″E) (VVV10.1) is located on the southern coastal plains of South Africa (Quick et al. 2016), a stretch of land bordering the Atlantic Ocean in the south, isolated from inland South Africa by the mountainous Cape Fold Belt (Figure 3B). These wetlands encompass a catchment of c. 0.5 km² and are situated on the landward edge of the Wilderness embayment at an elevation of 153 m asl. Vankervelsvlei is hydrologically isolated from the regional aquifer and fed exclusively by rainfall (Roets et al. 2008). Today the local vegetation is dominated by Cyperaceae mats floating on the wetland, fynbos-dominated vegetation (e.g. *Passerina*, *Ericaceae*, *Leucadendron* and *Restionaceae*) on the wetland's margins, and Afrotemperate forest types to the north (including *Ocotea*, *Olea* and *Podocarpus*). Compton (2011) proposed that these isolated coastal plains could be the geographical point of origin for AMH, suggesting the periodic sea-level changes
induced by interglacial-glacial cycles provoked competition and innovation. However, subsequent research, based on mitochondrial DNA lineages, indicated that *H. sapiens* migrated to the southern African coast from wetlands in modern-day Botswana *c.* 100 ka (Chan *et al.* 2019); although these interpretations have been subsequently challenged (Schlebusch *et al.* 2021) so uncertainty prevails. However, the region remains important from an evolutionary perspective because it contains the Blombosgrot cave which is one of the most prominent archaeological sites in southern Africa regarding the cultural development in *H. sapiens* (Douze *et al.* 2015). The Blombosgrot cave, located 160 km west of Vankervelsvlei, has been inhabited since at least 140 ka (Jacobs *et al.* 2006) and contains toolkits providing evidence for long-term planning and an elementary knowledge of chemistry *c.* 100 ka (Henshilwood *et al.* 2011).

The VVV10.1 record has a basal age in MIS 6.3 (146 ka), but no pollen was preserved until MIS 5.5 (122 ka), with another hiatus in the record during MIS 3.0-2.0 (24-12 ka). Afromontane forest taxa, predominantly *Podocarpus*, characterize the early sections but are barely found throughout the rest of the pollen record. Percentages for Afromontane taxa vary from *c.* 5 to *c.* 15% in MIS 5.4-5.3 (107-99 ka), but gradually decline until they are lost from the record in late MIS 5 and only sporadically occur in trace amounts thereafter. The most dominant vegetational elements between MIS 5.4 and 5.3 (107-99 ka) are the fynbos taxa. Among the fynbos taxa, Ericaceae is particularly abundant (reaching *c.* 40%), with *Stoebe* (20%) also significant. Subsequently, Ericaceae abundance remains high (average *c.* 60%) until MIS 3.0 (24 ka). The Ericaceae record starts declining around the transition to MIS 2.0 to about 45%. In the following *c.* 15 kyr pollen is poorly preserved, but Ericaceae ends up with percentages less than 5% in the most recent samples, which are dominated by unprecedented high values of Cyperaceae of over 40%.

### 23.4.3 Lake Magadi, Kenya

Lake Magadi is a seasonally flooded pan with a surface catchment of *c.* 100 km², situated 606 m asl in the south Kenyan part of the east African Rift Valley (Figure 3C). The Lake Magadi record (MAG14-2A) (Owen *et al.* 2018), was chosen based on its proximity (*c.* 25 km) to the Olorgesailie archaeological site (Behrensmeyer *et al.* 2002) and its length; covering the past one million years. The core was drilled as part of The Hominin Sites and Palaeolakes Drilling Project (HSPDP) initiative (Campisano *et al.* 2017). The Olorgesailie site is of particular interest because its archaeological surveys document a transition from the Acheulean to the Middle Stone Age mode of stone toolmaking between *c.* 320 and 305 ka (Brooks *et al.* 2018; Deino *et al.* 2018). This period of technological and cultural development is itself associated with the evolution of *H. sapiens*. Furthermore, this core is also the closest to the archaeological sites which have yielded the earliest recognized anatomically modern *H. sapiens* fossils in eastern-Africa, Omo Kibish (*c.* 195 kyr BP) and Herto (*c.* 160 kyr BP) at 700 and 1400 km respectively, both in Ethiopia.

The pollen record of MAG14-2A shows vegetation change over the last 500 ka, although the MIS 11.2 to 9.0 interval (375-303 ka) is devoid of pollen. Pre-500 ka vegetation was dominated locally by Poaceae and Cyperaceae, both making up 80% in at least one sample dated before the onset of MIS 13.13 (502 ka). Afromontane forest taxa make up the majority of the regional pollen signal, and *Podocarpus* dominates this regional signal with percentages of *c.* 80%, indicating a significant presence of arboreal taxa. By MIS 13 the pollen spectra seem to represent dry open grassland, almost completely comprised of Poaceae and deprived of arboreal taxa, except for low (*c.* 10%) percentages of *Podocarpus*. Poaceae shows a stable representation during the subsequent 125 ka, while both Cyperaceae and *Podocarpus* show an almost linear increase in representation. Although the following 75 kyr were not sampled, percentages of both local and regional pollen taxa seem to remain stable, potentially suggesting stable environmental conditions during this interval. Vegetation diversifies with the onset of MIS 6.6 (183 ka), during which *Olea, Juniperus, Commiphora, Acacia* and Amaranthaceae fluctuate between 0 and 40%.
### 23.4.4 Lake Malawi, Malawi

The sediment records MAL05-1B and -1C (Beuning et al. 2011; Ivory et al. 2018) were retrieved from Lake Malawi, the southernmost lake in the east African Rift Valley system (Figure 3D). Lake Malawi at 472 m asl has a surface area of c. 29,500 km² and a catchment area of c. 65,000 km² bordering the Rungwe volcanic highlands in the north and the Nyika plateau in the west. The mountainous topography means that the modern vegetation surrounding Lake Malawi is characterised by Afromontane forests (*Podocarpus*) and Afromontane grasslands in the west, while scrubland and woodland vegetation types can be found east of Lake Malawi. Despite the absence of AMH fossils in the vicinity of Lake Malawi, the vegetation records from the MAL05-1B/1C records are still relevant to AMH dispersal. The location of origin of AMH and the direction of their dispersal events is still debated; both southern Africa (e.g. Jacobs et al. 2008; Schlebusch et al. 2017) and north-eastern Africa (e.g. Lamb et al. 2018; Walter et al. 2000) have been proposed as regions harbouring the population of early humans that would ultimately disperse throughout the rest of the world. This makes Lake Malawi a likely passing point in the corridor used in either a northward or a southward dispersal of these AMH.

MAL05-1B and MAL05-1C together comprise 170 metres of sediment, of which 1C represents the youngest 62 metres and 1B the older 108. The MAL05-1B/1C pollen stratigraphy shows distinct antiphasing between periods of high arboreal (i.e. *Podocarpus*) pollen and periods with a distinct presence of non-arboreal (notably Poaceae) pollen. These arboreal phases are marked by analogous trends in other Afromontane taxa (e.g. *Apodytes*, *Ericaceae*, *Ilex*, *Juniperus*, *Kigge-laria*, *Myrtaceae*, *Olea* and *Syzygium*), and palynological studies on contemporary Afromontane forest suggests that *Podocarpus* percentages of >40% indicate dense forests, reaching all the way down to the shores of Lake Malawi (Ivory et al. 2018). The non-arboreal phases (indicated by grasses, herbs like Amarathaceae or woodland trees such as *Acacia*) on the other hand are indicative of dry woodland/wooded grassland type of ecosystems. In total the MAL05-1B/1C cores both record seven forest phases and seven grassland phases over the past 500 kyr. These start with a grassland phase (c. 75% Poaceae) lasting until MIS 12.4 (470 ka), when an extensive forested period is initiated for the subsequent 200 kyr. During this phase *Podocarpus* percentages fluctuate between c. 45% (MIS 12.32 and MIS 11.2, 450 and 375 kyr respectively) and c. 10% (MIS 9.2, 325 kyr), averaging on c. 30%. While *Podocarpus* percentages of 10% are low, arboreal taxa still maintain a relative dominance over non-arboreal pollen due to high percentages of *Celtis* (c. 15%), especially during MIS 11.2. Subsequent transitions between forest and open ecosystems are more frequent. Throughout the remainder of MAL05-1B we find four more grassland phases; MIS 8.4-7.5 (274-241 ka), MIS 7.2-7.0 (209-193 ka), MIS 6.6-6.5 (189-165 ka) and MIS 6.2 (142-137 ka), interspersed with forest phases at MIS 7.5-7.2 (241-209 ka), MIS 6.6 (193-189 ka) and MIS 6.5-6.2 (165-142 ka).

The base of record MAL05-1C (Beuning et al. 2011) is dated to the later part of MIS 6.2 (135 ka), and immediately records an increase in *Podocarpus* from near absence to c. 35% during the period MIS 6.2-6.0 (135-128 ka). A similar increase in *Podocarpus* is noted at the start of MIS 5 (between MIS 5.5 and 5.4 (122-107 ka)). Both these increases in *Podocarpus* are concomitant with an opposite trend in Poaceae percentages, which shows values of 80% between MIS 6 and 5.5 (122 ka), but 40-30% before and after this interval. The halfway point of MIS 5 is marked by a decline of *Podocarpus* percentages again coeval with another increase in Poaceae. Poaceae reaches its maximum at MIS 5.2 (87 ka) when its pollen make up nearly 100% of the pollen spectra. Samples from MIS 4 onwards show Poaceae stabilizing at 40%, a value that continues throughout the rest of the record, except for a short increase to c. 60% and a short depression to c. 20% at MIS 4.2 (65 ka) and 3.3 (53 ka), respectively. Meanwhile, *Podocarpus* enters the regional vegetation again in MIS 4, showing percentages of 10% over a period of c. 10 kyr and reaching c. 30% between MIS 4.2 and 3.3 before it decreases again to 10%, a value which is maintained throughout the remainder of the record. Prior to the peak in *Podocarpus*,
peaks in other montane and woodland taxa (e.g. *Acalypha*, *Acanthaceae*, *Blighia*, *Combretaceae*, *Craterispermum*, *Commiphora*, *Lannea*, *Maclura* and *Mimosaceae*), as well as maximum values in evergreen trees (e.g. *Alchornea*, *Celtis*, *Faurea*, *Ixora*, *Macaranga*, *Moraceae*, *Myrica* and *Trema*), are shown in the pollen record (c. 10%, 20% and 20%, respectively), after which all three groups continue at c. 10% throughout the rest of the record.

### 23.4.5 Lake Bambili, Cameroon

The inclusion of Lake Bambili's pollen record (B12), given it has the shortest timeframe (90 ka) in this review, is justified by its close geographical proximity to the Cameroonian Shum Laka archaeological site (5°51'31" N, 10°4'40" E), situated c. 20 km southwest of Lake Bambili (Figure 3E). The oldest layer containing evidence of the presence of *H. sapiens* is dated c. 30 ka (Lipson et al. 2020), while the rest of the archaeological record also displays evidence of significant societal developments such as a transition period in tool use (sometimes referred to as the 'Stone to Metal age') between the end of the Later Stone Age at 8 ka and the beginning of the Iron Age at 2.5 ka, as well as evidence for foundation and early stages of agriculture (Lavachery 2001). Lake Bambili is a high-altitude (2273 m asl) crater lake, currently enclosed locally by Afromontane forests characterized by the conifer *Podocarpus milanijanus* (Lézine et al. 2019), while the vegetation transitions to Afroalpine grasslands at higher altitudes and a mosaic of submontane forests and savannahs at lower altitudes (Lézine et al. 2013).

The initial aim of the palynological record presented in Lézine et al. (2019) was to reconstruct the history of Afromontane forests and their responses to glacial-interglacial cycles. Nevertheless, the pollen assemblages at Bambili can also be used to infer the landscape at a regional scale. The base of record B12 is dated to MIS 5.3 (99 ka), and the record starts off with percentages of *Podocarpus* that decrease from c. 25% to <5% just before the onset of MIS 5.1 (80 ka), while Poaceae show a coeval increase from 50% to 90%. Trace amounts (<5%) of other taxa are also present during this interval, e.g. Ericaceae, *Olea*, Asteraceae and *Alchornea*. This is immediately succeeded by a reversal in the trends of the two dominating taxa, and the representation of *Podocarpus* reaches c. 60% during MIS 5.1 at 75 ka, concurrent with a drop of Poaceae to <5%. During these extreme values, *Olea*, *Syzygium*, *Schefflera* and Asteraceae are also present in low quantities. Following the start of MIS 4 (71 ka), *Podocarpus* and Poaceae trends reverse again. *Podocarpus* remain practically absent (<5%) from the record in the MIS 5.0-3.3 (71-53 ka) interval, all the while Poaceae holds a stable presence, fluctuating between 70-80% and Ericaceae and Asteraceae fluctuate around 5%. MIS 3.3 sees *Podocarpus* reappearing in the record with c. 10%, and Poaceae starts a slow decline to 40% at 45 ka, but both taxa return to percentages similar to those in the MIS 5.0-3.3 interval at the 37 ka mark until Poaceae starts decreasing MIS 2.2 (19 ka). The gradual decrease of Poaceae lasts until it reaches c. 0% at 10 ka, and stays like this until c. 3 ka. During this 7 kyr interval *Podocarpus*, *Olea*, *Alchornea*, *Syzygium*, and *Schefflera* reappear in the pollen record but get replaced by Poaceae in the modern vegetation (3-0 ka).

### 23.4.6 Lake Bosumtwi, Ghana

Core BOS04-5B was retrieved from Lake Bosumtwi, Ghana (Koeberl et al. 2007), with the intent of exploring the vegetational compositions of tropical western Africa in response to changes in regional climate during the Quaternary. Lake Bosumtwi (6°30'6.04"N, 1°24'52.14"W) is situated in a meteorite impact crater formed 1.08 ± 0.04 million years ago (Jourdan et al. 2009) with a diameter of c. 11 km (Figure 3F). The bedrock and crater walls formed by this impact cause the lake's isolation from any regional bodies of water, precipitation being the only influx of water to the sedimentary archive. This closed hydrology makes the lake sensitive to regional climate change and precipitation in particular (Shanahan et al. 2012). The current lake surface of