# Quaternary Vegetation Dynamics – The African Pollen Database

Jürgen Runge, William Gosling, Anne-Marie Lézine, Louis Scott

► To cite this version:

Jürgen Runge, William Gosling, Anne-Marie Lézine, Louis Scott. Quaternary Vegetation Dynamics – The African Pollen Database. CRC Press, 35, 2021, Palaeoecology of Africa, Jürgen Runge, 978-0-367-75508-9. 10.1201/9781003162766. hal-03970034

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# Quaternary Vegetation Dynamics
The African Pollen Database

Jürgen Runge

Guest editors
William D. Gosling
Anne-Marie Lézine
Louis Scott

<figure><img src="image_3.png" /></figure>

CRC Press
Taylor & Francis Group

<figure><img src="image_4.png" /></figure>
QUATERNARY VEGETATION DYNAMICS –
THE AFRICAN POLLEN DATABASE
# Palaeoecology of Africa

International Yearbook of Landscape Evolution and
Palaeoenvironments

ISSN 2372-5907

Volume 35

Editor in Chief

J. Runge, Frankfurt, Germany

## Editorial board

G. Botha, Pietermaritzburg, South Africa

E. Cornelissen, Tervuren, Belgium

J. Eisenberg, Frankfurt, Germany

P. Giresse, Perpignan, France

K. Heine, Regensburg, Germany

S. Kröpelin, Köln, Germany

T. Huffmann, Johannesburg, South Africa

E. Latrubesse, Goiânia, Brazil

J. Maley, Montpellier, France

J.-P. Mund, Eberswalde, Germany

D. Olago, Nairobi, Kenya

F. Runge, Altendiez, Germany

L. Scott, Bloemfontein, South Africa

I. Stengel, Windhoek, Namibia

F.A. Street-Perrott, Swansea, United Kingdom
# Quaternary Vegetation Dynamics – The African Pollen Database

Series Editor

## Jürgen Runge

Goethe Universität, FB 11: Institut für Physische Geographie & Zentrum für interdisziplinäre Afrikaforschung (ZIAF), Frankfurt am Main, Germany

Guest Editors

## William D. Gosling

Ecosystem & Landscape Dynamics, Institute for Biodiversity & Ecosystem Dynamics (IBED), Faculty of Science, University of Amsterdam, Amsterdam, The Netherlands

## Anne-Marie Lézine

Laboratoire d'Océanographie et du Climat: expérimentations et modélisations numériques, Sorbonne Université, Paris, France

## Louis Scott

Faculty of Natural and Agricultural Sciences, University of the Free State, Bloemfontein, Republic of South Africa

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CRC Press

Taylor & Francis Group

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London

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Leiden

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Taylor & Francis Group, an informa business

A BALKEMA BOOK
CRC Press/Balkema is an imprint of the Taylor & Francis Group, an informa business

© 2022 Selection and editorial matter, the editors; individual chapters, the contributors

Typeset by MPS Limited, Chennai, India

The right of the Editors to be identified as the author of the editorial material, and of the
authors for their individual chapters, has been asserted in accordance with sections 77 and
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The Open Access version of this book, available at www.taylorandfrancis.com,
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Although all care is taken to ensure integrity and the quality of this publication and the
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*Library of Congress Cataloging-in-Publication Data*

A catalog record for this book has been requested

Published by: CRC Press/Balkema

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e-mail: Pub.NL@taylorandfrancis.com

www.routledge.com – www.taylorandfrancis.com

ISBN: 978-0-367-75508-9 (Hbk)

ISBN: 978-1-003-16276-6 (eBook)

ISBN: 978-0-367-75510-2 (Pbk)

DOI: 10.1201/9781003162766
# Contents

FOREWORD ix

—William D. Gosling, Anne-Marie Lézine, Louis Scott & Jürgen Runge

CONTRIBUTORS xi

CHAPTER 1 RISE OF THE PALAEOECOLOGY OF AFRICA SERIES 1

—Louis Scott

CHAPTER 2 THE AFRICAN POLLEN DATABASE (APD) AND TRACING ENVIRONMENTAL CHANGE: STATE OF THE ART 5

—Anne-Marie Lézine, Sarah Ivory, William D. Gosling & Louis Scott

CHAPTER 3 PRELIMINARY EVIDENCE FOR GREEN, BROWN AND BLACK WORLDS IN TROPICAL WESTERN AFRICA DURING THE MIDDLE AND LATE PLEISTOCENE 13

—William D. Gosling, Crystal N.H. McMichael, Zoë Groenewoud, Eleonora Roding, Charlotte S. Miller & Adele C.M. Julier

CHAPTER 4 HOLOCENE HIGH-ALTITUDE VEGETATION DYNAMICS ON EMI KOUSSI, TIBESTI MOUNTAINS (CHAD, CENTRAL SAHARA) 27

—Michèle Dinies, Lena Schimmel, Philipp Hoelzmann, Stefan Kröpelin, Frank Darius & Reinder Neef

CHAPTER 5 TIMING AND NATURE OF THE END OF THE AFRICAN HUMID PERIOD IN THE SAHEL: INSIGHT FROM POLLEN DATA 51

—Kévin Lemonnier & Anne-Marie Lézine

CHAPTER 6 CHANGES IN THE WEST AFRICAN LANDSCAPE AT THE END OF THE AFRICAN HUMID PERIOD 65

—Anne-Marie Lézine, Kévin Lemonnier, Martyn P. Waller, Ilham Bouimetarhan & Lydie Dupont

CHAPTER 7 RECONSTRUCTING VEGETATION HISTORY OF THE OLORGESAILIE BASIN DURING THE MIDDLE TO LATE PLEISTOCENE USING PHYTOLITH DATA 85

—Rahab N. Kinyanjui, Michael Meadows, Lindsey Gillson, Marion K. Bamford, Anna K. Behrensmeyer & Richard Potts
<table>
  <tbody>
    <tr>
      <td>CHAPTER 8</td>
      <td>SEDIMENTOLOGICAL, PALYNOLOGICAL AND CHARCOAL ANALYSES OF THE HYDRIC PALUSTRINE SEDIMENTS FROM THE LIELERAI-KIMANA WETLANDS, KAJIADO, SOUTHERN KENYA<br/>—Esther N. Githumbi, Colin J. Courtney Mustaphi &amp; Robert Marchant</td>
      <td>107</td>
    </tr>
    <tr>
      <td>CHAPTER 9</td>
      <td>THE NEW GARBA GURACHA PALYNOLOGICAL SEQUENCE: REVISION AND DATA EXPANSION<br/>—Graciela Gil-Romera, Mekbib Fekadu, Lars Opgenoorth, David Grady, Henry F. Lamb, Lucas Bittner, Michael Zech &amp; Georg Miehe</td>
      <td>127</td>
    </tr>
    <tr>
      <td>CHAPTER 10</td>
      <td>LOWER TO MID-PLIOCENE POLLEN DATA FROM EAST AFRICAN HOMINID SITES, A REVIEW<br/>—Raymonde Bonnefille &amp; Benjamin Bourel</td>
      <td>135</td>
    </tr>
    <tr>
      <td>CHAPTER 11</td>
      <td>ECOSYSTEM CHANGE AND HUMAN-ENVIRONMENT INTERACTIONS OF ARABIA<br/>—Sarah J. Ivory, Michèle Dinies &amp; Anne-Marie Lézine</td>
      <td>157</td>
    </tr>
    <tr>
      <td>CHAPTER 12</td>
      <td>THE CHALLENGE OF POLLEN-BASED QUANTITATIVE RECONSTRUCTION OF HOLOCENE PLANT COVER IN TROPICAL REGIONS: A PILOT STUDY IN CAMEROON<br/>—Marie-José Gaillard, Esther Githumbi, Gaston Achoundong, Anne-Marie Lézine, Christelle Hély, Judicaël Lebamba, Laurent Marquer, Florence Mazier, Furong Li &amp; Shinya Sugita</td>
      <td>183</td>
    </tr>
    <tr>
      <td>CHAPTER 13</td>
      <td>A HOLOCENE POLLEN RECORD FROM MBOANDONG, A CRATER LAKE IN LOWLAND CAMEROON<br/>—Keith Richards</td>
      <td>207</td>
    </tr>
    <tr>
      <td>CHAPTER 14</td>
      <td>FUTURE DIRECTIONS OF PALAEOECOLOGICAL RESEARCH IN THE HYPER-DIVERSE CAPE FLORISTIC REGION: THE ROLE OF PALYNOLOGICAL STUDIES<br/>—Lynne J. Quick</td>
      <td>225</td>
    </tr>
    <tr>
      <td>CHAPTER 15</td>
      <td>AN ATLAS OF SOUTHERN AFRICAN POLLEN TYPES AND THEIR CLIMATIC AFFINITIES<br/>—Manuel Chevalier, Brian M. Chase, Lynne J. Quick &amp; Louis Scott</td>
      <td>239</td>
    </tr>
    <tr>
      <td>CHAPTER 16</td>
      <td>POLLEN PRODUCTIVITY ESTIMATES FROM KWAZULU-NATAL DRAKENSBERG, SOUTH AFRICA<br/>—Trevor R. Hill, Tristan J. Duthie &amp; Jane Bunting</td>
      <td>259</td>
    </tr>
    <tr>
      <td>CHAPTER 17</td>
      <td>MODERN POLLEN-VEGETATION RELATIONSHIPS IN THE DRAKENSBERG MOUNTAINS, SOUTH AFRICA<br/>—Trevor R. Hill &amp; Jemma M. Finch</td>
      <td>275</td>
    </tr>
  </tbody>
</table>
<table>
  <tbody>
    <tr>
      <td>CHAPTER 18</td>
      <td>A LATE HOLOCENE POLLEN AND MICROCHARCOAL RECORD FROM EILANDVLEI, SOUTHERN CAPE COAST, SOUTH AFRICA<br/>—Nadia du Plessis, Brian M. Chase, Lynne J. Quick &amp; Michael E. Meadows</td>
      <td>293</td>
    </tr>
    <tr>
      <td>CHAPTER 19</td>
      <td>A c. 650 YEAR POLLEN AND MICROCHARCOAL RECORD FROM VANKERVELSVLEI, SOUTH AFRICA<br/>—Nadia du Plessis, Brian M. Chase, Lynne J. Quick, Paul Strobel, Torsten Haberzettl &amp; Michael E. Meadows</td>
      <td>301</td>
    </tr>
    <tr>
      <td>CHAPTER 20</td>
      <td>POLLEN RECORDS OF THE 14TH AND 20TH CENTURIES AD FROM LAKE TSIZAVATSY IN SOUTHWEST MADAGASCAR<br/>—Estelle Razanatsoa, Lindsey Gillson, Malika Virah-Sawmy &amp; Stephan Woodborne</td>
      <td>309</td>
    </tr>
    <tr>
      <td>CHAPTER 21</td>
      <td>MODERN POLLEN STUDIES FROM TROPICAL AFRICA AND THEIR USE IN PALAEOECOLOGY<br/>—Adele C.M. Julier, Saúl Manzano, Estelle Razanatsoa, Andriantsilavo H.I. Razafimanantsoa, Esther Githumbi, Donna Hawthorne, Glory Oden, Lisa Schüler, Monique Tossou &amp; Jane Bunting</td>
      <td>317</td>
    </tr>
    <tr>
      <td>CHAPTER 22</td>
      <td>VEGETATION RESPONSE TO MILLENNIAL- AND ORBITAL-SCALE CLIMATE CHANGES IN AFRICA: A VIEW FROM THE OCEAN<br/>—Ilham Bouimetarhan, Lydie Dupont, Hanane Reddad, Asmae Baqloul &amp; Anne-Marie Lézine</td>
      <td>349</td>
    </tr>
    <tr>
      <td>CHAPTER 23</td>
      <td>INSIDE-OF-AFRICA: HOW LANDSCAPE OPENNESS SHAPED HOMO SAPIENS EVOLUTION BY FACILITATING DISPERSAL AND GENE-FLOW IN MIDDLE AND LATE PLEISTOCENE AFRICA<br/>—Mick N.T. Bönnen, William D. Gosling &amp; Henry Hooghiemstra</td>
      <td>373</td>
    </tr>
    <tr>
      <td>CHAPTER 24</td>
      <td>THE ROLE OF PALAEOECOLOGY IN CONSERVING AFRICAN ECOSYSTEMS<br/>—Lindsey Gillson</td>
      <td>397</td>
    </tr>
    <tr>
      <td>REGIONAL INDEX</td>
      <td></td>
      <td>411</td>
    </tr>
    <tr>
      <td>SUBJECT INDEX</td>
      <td></td>
      <td>415</td>
    </tr>
    <tr>
      <td>BOOK SERIES PAGE</td>
      <td></td>
      <td>419</td>
    </tr>
  </tbody>
</table>
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Taylor & Francis

Taylor & Francis Group

http://taylorandfrancis.com
# Foreword

The "Quaternary Vegetation Dynamics", and the 35th volume of *Palaeoecology of Africa* (PoA) was born out of two workshops organised to relaunch the African Pollen Database initiative in Bondy near Paris (October 2019) and Amsterdam (January 2020). These workshops brought together researchers from around the world to showcase their work from across the African continent and to train them in data management. The training at the workshop was led by the late Eric Grimm who sadly passed away in November 2020. We hope that Eric's enthusiasm for collating, standardising, and disseminating palaeoecological data is captured in this volume.

In total this volume of PoA, that for the first time is available as an OPEN ACCESS publication, contains twenty-four papers and is organised regionally following the format of the first meeting: western Africa (chapters 3–6), eastern Africa and Arabia (chapters 7–11), central Africa (chapters 12–13), southern Africa (chapters 14–19), islands in the vicinity of Africa (chapter 20), and pan-African syntheses (chapters 21–24). With a view to stimulate primary research and mobilise open access publication of palaeoecological data two types of primary research papers are included: (i) short data papers containing descriptions of new palaeoecological data sets (chapters 9, 18, 19, 20), and (ii) longer research papers providing more in-depth analysis (chapters 3, 4, 5, 7, 8, 12, 13, 15, 16 and 17). To provide a synthetic overview of the state of research into Quaternary Vegetation Dynamics from in and around Africa we also include short perspective papers to provide insights into key regions or issues (chapters 1, 2, 14, and 24), and extensive review papers which bring together the growing body of research from around the continent to address particular scientific questions (chapters 6, 10, 11, 21, 22 and 23).

We are delighted to have been able to bring together work from all parts of Africa focused on the Quaternary. We believe that this reflects the enthusiasm and urgency for this type of palaeoecological research. As current climatic and land-use changes continue to exert pressure on the modern ecosystems, turning to the record of past environmental change to shed light on their origins, resilience and trajectories of change becomes increasingly pertinent. While the record of past change cannot be used to define how we should manage and develop ecosystems today, we hope that it can provide a frame of reference and inspiration for managers and policy makers to work with. We hope that the data, research and syntheses provided in this volume forms a solid basis for the next generation of palaeoecological researchers from Africa to provide scientifically and societally relevant information that will assist with the development of sustainable management practices.

Finally, we would like to thank all the participants in the meetings, the authors and the reviewers whose contributions have made this volume possible. We would like to also thank the French Agence Nationale pour la Recherche and the Belmont-Forum (VULPES: ANR-15-MASC-0003 and ACCEDE: 18 BELM 0001 05) who have provided financial support for the meetings and publication of this volume. We also take this opportunity to place on record our gratitude to Senior Publisher Janjaap Blom and his team from Routledge/Taylor & Francis/CRC Press for the continuous support to PoA.

Guest Editors: William D. Gosling (Amsterdam),
Anne-Marie Lézine (Paris),
and Louis Scott (Bloemfontein)

Series Editor: Jürgen Runge (Frankfurt)
February 2021
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Taylor & Francis

Taylor & Francis Group

http://taylorandfrancis.com
# Contributors

**Gaston Achoundong**

National Herbarium, IRAD, Yaoundé, Cameroon, Email: gachoundong@yahoo.fr
ORCID: https://orcid.org/0000-0001-6298-5763

**Marion. K. Bamford**

The Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg Private
Bag 3. Wits, 2050, South Africa, Email: marion.bamford@wits.ac.za
ORCID: https://orcid.org/0000-0003-0667-130X

**Asmae Baqloul**

Faculté des Sciences, Ibn Zohr University, B.P. 8106 Agadir, Morocco,
Email: asmaebaqloul@gmail.com
ORCID: https://orcid.org/0000-0002-7700-9535

**Anna K. Behrensmeyer**

Department of Paleobiology, Smithsonian Institution, P.O Box 37012, Washington,
DC 20013-7012, USA, Email: behrensa@si.edu
ORCID: https://orcid.org/0000-0001-6857-368X

**Lucas Bittner**

Heisenberg Chair of Physical Geography, Technische Universität, Dresden, Dresden,
Germany, Email: lucas.bittner@tu-dresden.de
ORCID: https://orcid.org/0000-0003-2521-5596

**Mick. N. T. Bönnen**

Institute for Biodiversity & Ecosystems Dynamics, University of Amsterdam,
Amsterdam, The Netherlands, Email: mickbonnen@hotmail.com
ORCID: https://orcid.org/0000-0002-0867-9949

**Raymonde Bonnefille**

Honorary Director of Research, CNRS, CEREGE, Aix Marseille University, CNRS,
IRD, INRAE, Coll. France, Technopole Arbois-Méditerranée,
13545 Aix en Provence cedex 4, France, Email: rbonnefille@orange.fr
ORCID: https://orcid.org/0000-0002-7912-9186

**Ilham Bouimetarhan**

Faculté des Sciences appliquées, CUAM, Ibn Zohr University, Agadir, Morocco; and
MARUM-Center for Marine Environmental Sciences, University of Bremen, Leobener
Str. 8, 28359 Bremen, Germany, Email: bouimetarhan@uni-bremen.de
ORCID: https://orcid.org/0000-0003-3369-3811

**Benjamin Bourel**

CEREGE, Aix Marseille University, CNRS, IRD, INRAE, Coll. France, Technopole Arbois-Méditerranée, 13545 Aix en Provence cedex 4, France, Email: benjaminbourel1@gmail.com
ORCID: https://orcid.org/0000-0001-8312-5471
**Jane Bunting**

Department of Geography, Geology and Environment, Faculty of Science and Engineering,
University of Hull, UK, Email: m.j.bunting@hull.ac.uk
ORCID: https://orcid.org/0000-0002-3152-5745

**Brian M. Chase**

Institut des Sciences de l'Evolution-Montpellier (ISEM), University of Montpellier,
Centre National de la Recherche Scientifique (CNRS), EPHE, IRD, 34095 Montpellier,
France; and Department of Environmental and Geographical Science, University of
Cape Town, Rondebosch, South Africa, Email: brian.chase@umontpellier.fr
ORCID: https://orcid.org/0000-0001-6987-1291

**Manuel Chevalier**

Institute of Earth Surface Dynamics, Geopolis, University of Lausanne, Switzerland; and
Institute of Geosciences, Sect. Meteorology, Rheinische Friedrich-Wilhelms-Universität
Bonn, Auf dem Hügel 20, 53121 Bonn, Germany, Email: chevalier.manuel@gmail.com
ORCID: https://orcid.org/0000-0002-8183-9881

**Colin J. Courtney Mustaphi**

Geoecology, Department of Environmental Sciences, University of Basel, Basel,
Switzerland; Water Infrastructure and Sustainable Energy (WISE) Futures, Nelson Mandela
African Institution of Science & Technology, Tengeru, Arusha, Tanzania, and York Institute
for Tropical Ecosystems, Department of Environment and Geography, University of York,
United Kingdom, Email: colin.courtney-mustaphi@york.ac.uk
ORCID: https://orcid.org/0000-0002-4439-2590

**Frank Darius**

Technische Universität Berlin, Institute for Ecology, Berlin, Germany,
Email: frank.darius@fu-berlin.de

**Michèle Dinies**

Freie Universität Berlin, Institute of Geographical Sciences, Berlin, Germany; and German
Archaeological Institute (DAI), Scientific Department of the Head Office, Berlin, Germany,
Email: michele.dinies@fu-berlin.de
ORCID: https://orcid.org/0000-0003-2196-4418

**Nadia du Plessis**

Department of Environmental and Geographical Science, University of Cape Town,
Rondebosch, South Africa, Email: dup.nadia@gmail.com
ORCID: https://orcid.org/0000-0003-0290-4866

**Lydie Dupont**

MARUM - Center for Marine Environmental Sciences, University of Bremen,
Leobener Str. 8, DE 28359 Bremen, Germany, Email: ldupont@marum.de
ORCID: https://orcid.org/0000-0001-9531-6793

**Tristan J. Duthie**

Discipline of Geography, School of Agriculture, Earth and Environmental Science, University
of KwaZulu-Natal, Pietermaritzburg, South Africa; and University of Suwon, South Korea,
Email: tjduthie@gmail.com
**Mekbib Fekadu**

Department of Ecology, Philipps-Marburg University, Marburg, Germany; and Department of Biology, Addis Ababa University, Addis Ababa, Ethiopia, Email: mekbib_fekadu@yahoo.com

**Jemma Finch**

Discipline of Geography, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Pietermaritzburg, South Africa, Email: finchj@ukzn.ac.za
ORCID: https://orcid.org/0000-0002-6678-6910

**Marie-José Gaillard**

Department of Biology and Environmental Science, Linnaeus University, Kalmar, Sweden, Email: marie-jose.gaillard-lemdahl@lnu.se
ORCID: https://orcid.org/0000-0002-2025-410X

**Graciela Gil-Romera**

Department of Ecology, Philipps-Marburg University, Marburg, Germany; and IPE-CSIC, Avda. Montañana, 1005, 50059, Zaragoza, Spain, Email: graciela.gil@ipe.csic.es
ORCID: https://orcid.org/0000-0001-5726-2536

**Lindsey Gillson**

Plant Conservation Unit, Department of Biological Sciences, University of Cape Town, South Africa, Email: lindsey.gillson@uct.ac.za
ORCID: https://orcid.org/0000-0001-9607-6760

**Esther N. Githumbi**

Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden; and Department of Biology and Environmental Science, Linnaeus University, Kalmar, Sweden, Email: esther.githumbi@lnu.se
ORCID: https://orcid.org/0000-0002-6470-8986

**William D. Gosling**

Institute for Biodiversity and Ecosystems Dynamics, University of Amsterdam, Amsterdam, The Netherlands, Email: W.D.Gosling@uva.nl
ORCID: https://orcid.org/0000-0001-9903-8401

**David Grady**

Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, United Kingdom, Email: gradydai524@gmail.com
ORCID: https://orcid.org/0000-0002-8286-5010

**Zoë Groenewoud**

Institute for Biodiversity and Ecosystems Dynamics, University of Amsterdam, Amsterdam, The Netherlands, Email: groenewoud.zoe@gmail.com

**Torsten Haberzettl**

Physical Geography, Institute of Geography and Geology, University of Greifswald, Germany, Email: torsten.haberzettl@uni-greifswald.de
ORCID: https://orcid.org/0000-0002-6975-9774
**Donna Hawthorne**

School of Geography and Sustainable Development, Irvine Building, University of
St Andrews, UK, Email: dj43@st-andrews.ac.uk
ORCID: https://orcid.org/0000-0002-0104-473X

**Christelle Hély**

Institut des Sciences de l'Evolution de Montpellier, Université de Montpellier and Ecole
Pratique des Hautes Etudes, Université PSL, Paris, France, Email: christelle.hely@ephe.psl.eu
ORCID: https://orcid.org/0000-0002-7549-3239

**Trevor Hill**

Discipline of Geography, School of Agricultural, Earth and Environmental Sciences,
University of KwaZulu-Natal, Pietermaritzburg, South Africa, Email: HillT@ukzn.ac.za
ORCID: https://orcid.org/0000-0001-7015-6906

**Philipp Hoelzmann**

Freie Universität Berlin, Institute of Geographical Sciences, Berlin, Germany,
Email: philipp.hoelzmann@fu-berlin.de
ORCID: https://orcid.org/0000-0001-8709-8474

**Henry Hooghiemstra**

Institute for Biodiversity and Ecosystems Dynamics, University of Amsterdam, Amsterdam,
The Netherlands, Email: H.Hooghiemstra@uva.nl
ORCID: https://orcid.org/0000-0003-2502-1644

**Sarah J. Ivory**

Department of Geosciences, Pennsylvania State University, University Park, USA,
Email: ivorysj@gmail.com
ORCID: https://orcid.org/0000-0003-4709-4406

**Adele C.M. Julier**

Plant Conservation Unit, University of Cape Town, Cape Town, South Africa,
Email: adelejulier@gmail.com
ORCID: https://orcid.org/0000-0003-1106-6008

**Rahab N. Kinyanjui**

Department of Earth Sciences, National Museums of Kenya, P.O. Box 40658-00100 Nairobi,
Kenya; Department of Environmental & Geographical Science, University of Cape Town,
Rondebosch 7701, South Africa; School of Geographical Sciences, East China Normal
University, Shanghai 200241, China; and College of Geography and Environmental Sciences,
Zhejiang Normal University, Jinhua 321004, China, Email: rkinyanji@gmail.com
ORCID: https://orcid.org/0000-0003-2032-8321

**Stefan Kröpelin**

University of Cologne, Institute of Prehistoric Archaeology, Africa Research Unit, Cologne,
Germany, Email: s.kroe@uni-koeln.de
ORCID: https://orcid.org/0000-0002-6377-3401
**Henry F. Lamb**

Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, United Kingdom; and Department of Botany, Trinity College Dublin, Dublin, Ireland,
Email: hfl@aber.ac.uk

ORCID: https://orcid.org/0000-0003-0025-0766

**Judicaël Lebamba**

Département de Biologie, Université des Sciences et Techniques de Masuku, Franceville,
Gabon, Email: jlebamba@yahoo.fr

ORCID: https://orcid.org/0000-0002-4890-4215

**Kévin Lemonnier**

Laboratoire d'Océanographie et du Climat, Expérimentation et Approche Numérique/IPSL, Sorbonne Université, CNRS-IRD-MNHN, Paris, France, Email: kevin.lemonnier@locean.ipsl.fr

**Anne-Marie Lézine**

Laboratoire d'Océanographie et du Climat, Expérimentation et Approche Numérique/IPSL, Sorbonne Université, CNRS-IRD-MNHN, Paris, France, Email: anne-marie.lezine@locean.ipsl.fr

ORCID: https://orcid.org/0000-0002-3555-5124

**Furong Li**

School of Ecology, Sun Yat-sen University, Guangzhou, China, Email: lifr5@mail.sysu.edu.cn

ORCID: https://orcid.org/0000-0001-8717-502X

**Saúl Manzano**

Plant Conservation Unit, University of Cape Town, Cape Town, South Africa,
Email: saul.manzano.rodriguez@gmail.com

ORCID: https://orcid.org/0000-0002-5720-2768

**Robert Marchant**

York Institute for Tropical Ecosystems, Department of Environment and Geography,
University of York, York, United Kingdom, Email: robert.marchant@york.ac.uk

ORCID: https://orcid.org/0000-0001-5013-4056

**Laurent Marquer**

Institute of Botany, University of Innsbruck, Innsbruck, Austria, and Research Group for Terrestrial Palaeoclimates, Max Planck Institute for Chemistry, Mainz, Germany,
Email: Laurent.Marquer@uibk.ac.at

ORCID: https://orcid.org/0000-0002-5772-3782

**Florence Mazier**

Environmental Geography Laboratory, GEODE UMR-CNRS 5602, Université de Toulouse
Jean Jaurès, Toulouse, France, Email: florence.mazier@univ-tlse2.fr

ORCID: https://orcid.org/0000-0003-2643-0925
**Michael E. Meadows**

Department of Environmental and Geographical Science, University of Cape Town,
Rondebosch, South Africa; School of Geographic Sciences, East China
Normal University, Shanghai, China; and College of Geography and Environmental Sciences,
Zhejiang Normal University, China, Email: michael.meadows@uct.ac.za
ORCID: https://orcid.org/0000-0001-8322-3055

**Crystal N.H. McMichael**

Institute for Biodiversity and Ecosystems Dynamics, University of Amsterdam, Amsterdam,
The Netherlands. Email: C.N.H.McMichael@uva.nl
ORCID: https://orcid.org/0000-0002-1064-1499

**Georg Miehe**

Department of Geography, Philipps-Marburg University, Marburg, Germany,
Email: miehe@staff.uni-marburg.de
ORCID: https://orcid.org/0000-0002-9813-4909

**Charlotte S. Miller**

Leeds Trinity University, Leeds, United Kingdom, Email: lottie.miller2@gmail.com
ORCID: https://orcid.org/0000-0003-1547-1641

**Reinder Neef**

German Archaeological Institute (DAI), Scientific Department of the Head Office, Berlin,
Germany, Email: reinder.neef@dainst.de

**Glory Oden**

Department of Plant and Ecological Studies, University of Calabar, Calabar,
Nigeria, Email: gloryoden@unical.edu.ng
ORCID: https://orcid.org/0000-0002-3124-7853

**Lars Opgenoorth**

Department of Ecology, Philipps-Marburg University, Marburg, Germany,
Email: Opgenoorth@uni-marburg.de
ORCID: https://orcid.org/0000-0003-0737-047X

**Richard Potts**

Human Origins Program, P.O. Box 37012, Smithsonian Institution, Washington,
DC 20013-7012 USA, Email: pottsr@si.edu
ORCID: https://orcid.org/0000-0001-6008-0100

**Lynne J. Quick**

African Centre for Coastal Palaeoscience, Nelson Mandela University, Port Elizabeth,
South Africa, Email: lynne.j.quick@gmail.com
ORCID Number: https://orcid.org/0000-0002-6735-7106

**Andriantsilavo H.I. Razafimanantsoa**

Plant Conservation Unit, University of Cape Town, Cape Town, South Africa,
Email: tsilamiezaka3@gmail.com
ORCID: https://orcid.org/0000-0002-9933-6991
**Estelle Razanatsoa**

Plant Conservation Unit, Department of Biological Sciences, University of Cape Town,
South Africa, Email: estelle.razanatsoa@uct.ac.za
ORCID: https://orcid.org/0000-0002-7219-1411

**Hanane Reddad**

L'Ecole Supérieure de Technologie & Faculté des Lettres et des Sciences Humaines,
Sultan Moulay Slimane University, Beni Mellal, Morocco, Email: h.reddad@usms.ma
ORCID: https://orcid.org/0000-0002-6238-165X

**Keith Richards**

KrA Stratigraphic, 116 Albert Drive, Conwy, North Wales, LL31 9YY, United Kingdom; and
Department of Geography and Planning, University of Liverpool, L69 7ZT, United Kingdom,
Email: kr@paly.co.uk
ORCID: https://orcid.org/0000-0002-5158-8209

**Eleonora Roding**

Institute for Biodiversity and Ecosystems Dynamics, University of Amsterdam, Amsterdam,
The Netherlands, Email: eleonora.roding@gmail.com

**Lena Schimmel**

Freie Universität Berlin, Institute of Geographical Sciences, Berlin, Germany,
Email: lena.schimmel@fu-berlin.de
ORCID: https://orcid.org/0000-0002-8084-2915

**Lisa Schüler**

Department of Palynology and Climate Dynamics, Albrecht-von-Haller Institute for Plant
Sciences, Göttingen University, Göttingen, Germany, Email: lschuel@gwdg.de
ORCID: https://orcid.org/0000-0002-4116-1105

**Louis Scott**

Department of Plant Sciences, University of the Free State, Bloemfontein, South Africa,
Email: ScottL@ufs.ac.za
ORCID: https://orcid.org/0000-0002-4531-0497

**Paul Strobel**

Physical Geography, Institute of Geography, Friedrich Schiller University Jena, Germany,
Email: paul.strobel@uni-jena.de
ORCID: https://orcid.org/0000-0002-7860-5398

**Shinya Sugita**

Institute of Ecology, Tallinn University, Estonia, Email: sugita@tlu.ee
ORCID: https://orcid.org/0000-0002-3634-7095

**Monique Tossou**

Department of Plant Biology, University of Abomey-Calavi, Bénin, Email: tossoumonique@
gmail.com
ORCID: http://orcid.org/0000-0003-2397-728X
**Malika Virah-Sawmy**

Humboldt-Universitat zu Berlin, Geography, Germany, Email: malikavs@gmail.com
ORCID: https://orcid.org/0000-0003-3646-5646

**Martyn P. Waller**

Department of Geography and Geology, Kingston University London, Kingston upon Thames, Surrey, UK, Email: martyn.waller@kingston.ac.uk
ORCID: https://orcid.org/0000-0003-3876-2492

**Stephan Woodborne**

iThemba LABS, Johannesburg, South Africa, Email: swoodborne@tlabs.ac.za
ORCID: https://orcid.org/0000-0001-8573-8626

**Michael Zech**

Heisenberg Chair of Physical Geography, Technische Universität Dresden, Dresden, Germany, Email: mzech@msx.tu-dresden.de
ORCID: https://orcid.org/0000-0002-9586-0390
CHAPTER 1

Rise of the Palaeoecology of Africa series

Louis Scott

*Department of Plant Sciences, University of the Free State, Bloemfontein, South Africa*

ABSTRACT: The *Palaeoecology of Africa* series was founded by E.M. van Zinderen Bakker, a biologist and palynologist who emigrated from Europe to South Africa. Ever since its origin during the nineteen-sixties, it gave a reflection of the history and development of palaeoscience in connection with the African continent and played a role in promoting international collaboration with multidisciplinary reports, conference proceedings and other papers in this field.

**1.1 INTRODUCTION**

*Palaeoecology of Africa* (PoA) of which this is the 35th volume, is a series traditionally focusing on multi-disciplinary studies on palaeoenvironments of Africa, especially on more recent parts of geological time like the Neogene and Quaternary. The early PoA volumes reveal the development history of these palaeoscience aspects in Africa. Thanks to the pioneering and visionary efforts of Eduard Meine van Zinderen Bakker and the publisher A. A. Balkema, the early volumes of PoA was a unique academic initiative out of Africa in the nineteen sixties. The series served as a mouth piece for an international group of specialists at a time when the important role palaeoenvironmental changes did not yet receive as much attention as today. Palaeoscience was then, a little-known discipline for the continent except for a rich heritage of Palaeozoic fossils and a few important hominid cranial finds such as at such as Taung, Florisbad and a few other sites (e.g. Dart 1925; Dryer 1935).

**1.2 ORIGIN**

PoA had its humble origins in the late nineteen-fifties and early sixties when van Zinderen Bakker, a Dutch naturalist who immigrated to South Africa in 1947 (Meadows 2015; Neumann and Scott 2018) started lecturing at the University of the Orange Free State in Bloemfontein (now shortened to University of the Free State). Here, he formed the Palynological Research Unit that was sponsored by the South African Council for Scientific and Industrial Research, and by the 1950's he was already involved in some of the first palynogical research projects in Africa, including modern pollen surveys in Southern Africa (Coetzee and van Zinderen Bakker 1952) and analysis of the hominin-bearing spring deposits of Florisbad near Bloemfontein (Dreyer 1935; van Zinderen Bakker 1957).

PoA started as eight soft-cover reports on pollen analysis entitled 'Palynology of Africa' in which van Zinderen Bakker reported on research news and activities in palynology and related aspects of palaeosciences in Africa covering the period of 1950–1963 (referenced in Neumann and Scott 2018). They were later re-published by Balkema, Cape Town in 1966 in book form as Volume 1 of *Palaeoecology of Africa* with the sub-title *and the Surrounding Islands &*
*Antarctica* (Van Zinderen Bakker 1966). The sub-title reflected van Zinderen Bakker's wide multi-disciplinary interests, which included biological and palynological research at the Marion and Prince Edward Islands, c. 2000 km south east of Cape Town in the Southern Ocean, to which he organized the first biological and geological research expedition in 1965 (van Zinderen Bakker 1976a; Van Zinderen Bakker *et al.* 1971). PoA Volume 1 (Van Zinderen Bakker 1966) included accounts of activities of several well-known international scientist at the time like D.A. Livingstone, L.S.B. Leakey, J.D. Clarke, R.J. Mason, C.K. Brain, W.W. Bishop, A.R.H. Martin, M. van Campo, E.P. Plumstead, H. Rakotoarivelo, H. Straka, O. Hedberg, R.E. Moreau, W.F. Libby, and others.

Volume 2, 4 and 6 followed basically the same format as Volume 1, but contained chapters under specific topics as short reports by various authors (Van Zinderen Bakker 1966, 1967b, 1972). The chapter topics included climatology and palaeoclimatology, geology and palaeontology, archaeology, biogeography, palynology in Africa, Antarctica and the Southern Ocean, isotope dates and morphology of microfossils, periglacial evidence, sea-levels, and oceanography.

The third volume of Palaeoecology of Africa contained the doctoral thesis of Joey Coetzee (Coetzee 1967), which is a landmark publication for Quaternary palynology in Africa (Meadows 2007). The early volumes also included additional lists with researcher's addresses and publications.

Maintaining the wide multi-disciplinary character from an international group of palaeo-scientists, subsequent volumes of PoA began to include separately authored papers, e.g., Volume 7 that included an extended study of 106 pages by A.C. Hamilton on palynology in Uganda (Hamilton 1972).

## 1.3 EDITORIAL CHANGES

Over the years the series eventually changed editors or were assisted by guest editors especially in the case of conference proceedings. Volume 18 was edited by Joey Coetzee and served as a dedication to the work of van Zinderen Bakker (Table S1).

Klaus Heine of Regensburg took over as editor for Volumes 19-27, of which Volume 27 was co-edited by Jürgen Runge (Frankfurt) who took over the duties for the rest of the volumes. After 1999, CRC Press (Taylor & Francis Group/'A Balkema Book') became the publisher and introduced the new current enlarged layout format and new series sub-title, *Landscape evolution and Palaeoenvironments* since 2007 (Volumes 28–34).

## 1.4 CONFERENCE PROCEEDINGS

With the appearance of Volume 22 in 1991, the following seven of eleven conference proceedings, were already published in PoA of which four represented meetings of the Southern African Society for Quaternary Research (SASQUA) (see Table S1 for the full list):

(1) Volume 5, Scientific Committee on Antarctic Research (SCAR) of the International Council of Scientific Unions (ICSU) Cambridge in 1968 (Van Zinderen Bakker 1969). This was later followed up by Volume 8 (Van Zinderen Bakker 1973), which did not cover the proceedings of a specific event but expanded the topic and inspired further interest in history of Antarctica.

(2) Volume 12, Sahara and Surrounding Seas held in Mainz in 1979 under the auspices of the *Akademie der Wissenschaften und der Literatur*, guest edited by M. Sarnthein, E. Siebold and P. Rognon, (Van Zinderen Bakker and Coetzee 1979).

(3) Volume 15, Southern African Society for Quaternary Research, SASQUA VI (1981) Pretoria, guest edited by J.C. Vogel, E.A. Voigt and T.C. Partridge (Coetzee and van Zinderen Bakker 1982).
(4) Volume 17, Southern African Society for Quaternary Research, SASQUA VII (1985) Stellenbosch, guest edited by H. Deacon (Van Zinderen Bakker et al. 1986).

(5) Volume 19, Southern African Society for Quaternary Research, SASQUA VIII (1987) Bloemfontein, guest edited by J.A. Coetzee (Heine 1988).

(6) Volume 21 Southern African Society for Quaternary Research, SASQUA IX (1989) Durban, guest edited by R.R. Maud (Heine 1990).

(7) Volume 22 (African Palynology) Rabat, guest edited by A. Ballouche and J. Maley (Heine 1991).

## REFERENCES

Coetzee, J.A., 1967, Pollen analytical studies in east and Southern Africa. *Palaeoecology of Africa and the Surrounding Islands, 3* (A.A. Balkema: Cape Town).

Coetzee, J.A., van Zinderen Bakker, E.M., 1952, Pollen spectrum of the Southern Middleveld of the Orange Free State. *South African Journal of Science, 48* (9), pp. 275–281.

Coetzee, J.A., van Zinderen Bakker, E.M. 1982, *Palaeoecology of Africa and the Surrounding Islands, 15*, (Balkema: Cape Town).

Dart. R.A. 1925, Australopithecus africanus: The Man-Ape of South Africa. *Nature, 145* (2884), pp. 195–199, 10.1038/115195a0.

Dreyer, T.F., 1935, A Human Skull from Florisbad, Orange Free State, with a Note on the Endocranial Cast, by C.U. Ariens Kappers. *Verhandelingen der Koninklijke Nederlandse Akademie van Wetenschappen, 38*, pp. 3–12.

Hamilton, A.C. 1972, The interpretation of pollen diagrams from highland Uganda. *Palaeoecology of Africa, 7*, pp. 45–149 (A.A. Balkema: Cape Town).

Heine, K. 1988, *Palaeoecology of Africa and the Surrounding Islands, 19* (A.A. Balkema: Cape Town).

Heine, K. 1990, *Palaeoecology of Africa and the Surrounding Islands, 21* (A.A. Balkema: Cape Town).

Heine, K. 1991, *Palaeoecology of Africa and the Surrounding Islands, 22* (A.A. Balkema: Cape Town).

Meadows, M.E., 2007, Classics revisited – Coetzee, J.A. 1967: pollen analytical studies in east and southern Africa. *Palaeoecology of Africa 3*, 1–146. *Prog. Phys. Geogr.*, **31** (3), pp. 313–317, 10.1177/0309133307079056.

Meadows, M.E., 2015, Seven decades of Quaternary palynological studies in southern Africa: a historical perspective. *Trans. R. Soc. S. Afr.*, **70** (2), pp. 103–108, 10.1080/0035919X.2015.10.04139.

Neumann, F. and Scott, L., 2018, E.M. van Zinderen Bakker (1907–2002) and the study of African Quaternary palaeoenvironments, *Quaternary International*, **495**, 153–168, 10.1016/j.quaint.2018.04.017.

Van Zinderen Bakker, E.M., 1966, *Palaeoecology of Africa and the Surrounding Islands 1950–1963, 1*, (Balkema: Cape Town).

Van Zinderen Bakker, E.M., 1967a, The South African biological-geological survey of the Marion and Prince Edward Islands and the meteorological expedition to Bouvet Island – introduction. *South African Journal of Science* **63**(6), 217–218.

Van Zinderen Bakker, E.M., 1967b, *Palaeoecology of Africa and the Surrounding Islands 1964–1965, 2* (A.A. Balkema: Cape Town).

Van Zinderen Bakker, E.M., 1967, *Palaeoecology of Africa and the Surrounding Islands 1966–1965, 4* (A.A. Balkema: Cape Town).

Van Zinderen Bakker, E.M., 1969, *Palaeoecology of Africa and the Surrounding Islands, 5* (A.A. Balkema: Cape Town).
Van Zinderen Bakker, E.M., 1972, *Palaeoecology of Africa and the Surrounding Islands 1969–1971*, 6, (Balkema: Cape Town).

Van Zinderen Bakker, E.M., 1973, *Palaeoecology of Africa and the Surrounding Islands 8* (A.A. Balkema: Cape Town).

Van Zinderen Bakker, E.M., and Coetzee, J.A., 1979, *Palaeoecology of Africa and the Surrounding Islands*, 12, (A.A. Balkema: Cape Town).

Van Zinderen Bakker, E.M., Coetzee, J.A. and Scott, L., 1986, *Palaeoecology of Africa and the Surrounding Islands*, 17, (A.A. Balkema: Cape Town).

Van Zinderen Bakker, E.M., Winterbottom, J.M., and Dyer, R.A. (Eds.), 1971, *Marion and Prince Edward Islands. Report on the South African Biological and Geological Expedition, 1965–1966*. (A.A. Balkema: Cape Town).
CHAPTER 2

# The African Pollen Database (APD) and tracing environmental change: State of the Art

Anne-Marie Lézine

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

Sarah J. Ivory

*Department of Geosciences, Pennsylvania State University, University Park, USA*

William D. Gosling

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

Louis Scott

*Department of Plant Sciences, University of the Free State, Bloemfontein, South Africa*

**ABSTRACT:** The African Pollen Database is a scientific network with the objective of providing the international scientific community with data and tools to develop palaeoenvironmental studies in sub-Saharan Africa and to provide the basis for understanding the vulnerability of ecosystems to climate change. This network was developed between 1996 and 2007. It promoted the collection, homogenization and validation of pollen data from modern (trap, soils, lake and river mud) and fossil materials (Quaternary sites) and developed a tool to determine pollen grains using digital photographs from international herbaria. Discontinued in 2007 due to a lack of funding, this network now resumes its activity in close collaboration with international databases: Neotoma, USA, Pangaea, DE, and the Institut Pierre Simon Laplace, FR.

## 2.1 INTRODUCTION

International cooperation in research and decision-making is critical for solving global environmental problems linked to climate and/or human impact on ecosystems, particularly at regional level. These environmental problems include forest degradation, accelerating loss of biodiversity and water resources, instability of transitional ecological domains, and change in coastal zones. Tropical ecosystems are especially at risk as future states are likely to be beyond the range of observations, yet their preservation is of crucial importance for the maintenance of the Earth's biosphere and climate. For example, the role of the equatorial and tropical forests
in global exchanges, such as the global carbon cycle, is widely recognised (Detwiler and Hall 1988). Research developed within the general framework of international scientific programmes (e.g., the International Geosphere Biosphere Programme, IGBP – http://www.igbp.net/) have long highlighted the need to provide quantitative understanding of the Earth’s past environment in order to define the envelope of natural environmental variability within which we can assess anthropogenic impact on the Earth’s biosphere, geosphere and atmosphere. Following these rec-ommendations, the scientific community has developed a set of analytical techniques to recover high-resolution environmental and ecological records from different natural archives such as tree-rings, and lake and ocean sediments, thus providing accurate scientific information for the development of predictive models of regional and global change. The use of these data to test Earth system model simulations requires the collection, assemblation, standardization and sub-sequently the access to the wider scientific and modelling community in the form of specific regional databases.

## 2.2 MAIN ACHIEVEMENTS

The African Pollen Database (APD) was first developed in 1996 in close cooperation with its European counterpart (EPD) (European Pollen Database; http://www.europeanpollendatabase.net) and the Global Pollen Database hosted at the National Oceanic and Atmospheric Administration (NOAA) Paleoclimatology Database (USA) (https://www.ncdc.noaa.gov/data-access/paleoclimatology-data). The initial workshop and subsequent work, funded by the French National Centre for Scientific Research (CNRS), the European Union (International Cooperation for development (INCO-DEV) and European network of research and innovation centres (ENRICH) programmes and the UNESCO International Geoscience Programme (PICG), established methods of collating pollen data, developed a standardized pollen nomenclature (Vincens et al. 2007), generated updated age models, composed images of pollen grains from internationally recognized herbaria, and created a searchable web interface. In the first stage of its development, the APD contained 288 fossil sites and 1985 modern samples (Figure 1). Among the numerous achievements of the APD one can highlight the following topics.

### 2.2.1 Pollen based biome reconstructions

Jolly et al. (1998) first demonstrated that the ‘biomization’ method for assigning pollen taxa to plant functional types and biomes was able to predict the potential natural vegetation of tropical Africa, despite uncertainty and variability of pollen production and dissemination (Ritchie 1995) of an extremely biodiverse flora (26,000 plant species; Lebrun and Stork 1991–1997). This allowed palaeoecologists working in Africa to participate in the ‘BIOME 6000’ project sponsored by IGBP (Prentice and Webb 1998). This project aimed to use palaeoecological data from the mid-Holocene as a benchmark to evaluate simulations with coupled climate-biosphere models and thus to assess the extent of biogeophysical (vegetation-atmosphere) feedbacks in the global climate system (Prentice et al. 2000). After the validation of the modern pollen dataset (Gajewski et al. 2002; Jolly et al. 1998), the biomization method was successfully applied to reconstruct modern (Lézine et al. 2009; Vincens et al. 2006) and past biomes for selected time periods, typically the Last Glacial Maximum (LGM) and the Holocene (Jolly et al. 1998; Elenga et al. 2000). Past biome reconstructions have also been performed for the Plio-Pleistocene (Bonnefille et al. 2004; Novello et al. 2015) and more recent time periods such as the last glacial-interglacial cycle and the Holocene (Amaral et al. 2013; Izumi and Lézine 2016; Lebamba et al. 2012; Lézine et al. 2019).
<figure><img src="image_9.png" /><figcaption>**Figure 1.** Late Quaternary African Pollen Database (APD) sites. In red: pollen data gathered during the first phase of the APD (1994–2007). In yellow: new pollen sites to be entered into the new version of APD, in construction).</figcaption></figure>

## 2.2.2 Quantitative reconstructions of climate variables from pollen data

Modern-analogue, regression, and model-inversion techniques have been developed to reconstruct past climates from pollen assemblages or pollen-based reconstructed biomes worldwide. Using the APD modern pollen dataset, Peyron et al. (2007) provided the first quantitative pollen-based reconstruction of precipitation for all of Africa at 6000 yr BP based on the Modern Analogues Technique (MAT) and the Plant-Functional Types (PFT) climate relationships. Results were then compared with atmospheric general circulation model output and coupled ocean atmosphere-vegetation models developed in the frame of the Paleoclimate Model Intercomparison Project (PMIP) international project (Joussaume and Taylor 1995). More recently, Wu et al. (2007) then Izumi and Lézine (2016) developed an inverse modelling approach based on the BIOME model to quantitatively reconstruct past climates based on pollen biome scores. The advantage of this method was to provide quantitative climate reconstructions for periods when CO₂ concentrations were different from today. While reconstruction attempts of climate by means of pollen data in South Africa, were mostly qualitative (Scott et al. 2012), Chevalier and Chase (2015) applied a method that related the pollen to plant distribution data to obtain quantitative estimates.

## 2.2.3 Vegetation reconstructions from pollen data

Palaeoecological data from the APD led to a series of reconstructions of vegetation at a continental scale. Site-based global biome maps for Africa for the mid-Holocene and LGM were first completed within the framework of the 'BIOME 6000' project (Prentice et al. 2000). More recently, APD palaeoecological data was included in a global synthesis of changes in composition and structure of past vegetation since the LGM performed by Nolan et al. (2018). This study provided a baseline for evaluation of the magnitudes of ecosystem transformations under future emission scenarios.

At a regional scale, APD data were used to reconstruct the Green Sahara and evaluate plant migration rates during the African Humid Period (Hély et al. 2014; Watrin et al. 2009). In
East Africa, compilation of pollen and archaeological data was used to discuss the cumulative effects of climate and land-use on the environment (Marchant *et al.* 2018). Furthermore, with the increasing recognition that fossil data can improve information about fundamental climatic tolerances, modern and palaeoecological data from the APD have been included in estimates of climatic niches of at-risk plant taxa (Ivory *et al.* 2016). This information was then used to provide forecasts of future impacts to ranges under climate and land-use trajectories for the end of the 21st century (Ivory *et al.* 2019).

## 2.3 CHALLENGES AND FUTURE DEVELOPMENTS

All these realizations suffer from (1) an highly uneven geographic distribution of data. Pollen data are relatively abundant in Eastern and Southern Africa where palynological research has been ongoing since the early 1950s (Hedberg 1954; van Zinderen Bakker and Coetzee 1952). In the former region, the abundance of lakes and swamps also provides favourable conditions for pollen preservation and long-time series. In North and Central Africa, on the other hand, data are less numerous and often discontinuous in time. The drying out of Holocene lakes in the Sahara, the difficulties of access to the sites, and their rarity are all limitations to regional geographical reconstructions; (2) the scarcity of long time series beyond the LGM (Ivory et al. 2017; Lézine et al. 2019; Miller and Gosling 2014; Scott 2016), and therefore long-term vegetation changes are mostly derived from marine cores (e.g., Dupont and Kuhlmann 2017; Hessler et al. 2010).

Thanks to a recent funding from the Belmont Forum for Science-driven e-infrastructure innovation for the project ‘Abrupt Change in Climate and Ecosystems: Where are the Tipping points?’, the APD is now being relaunched and developing further collaborations with international databases (‘NEOTOMA’, ‘PANGAEA’) and the French Institute Pierre Simon Laplace (IPSL). One of the priorities is to gather and validate data published since 2007, the date of the closure of the French data centre Medias-France where APD was stored. Today, 67 new late Quaternary, 17 Plio-Pleistocene and 20 marine new pollen series have been collated. Strong links are being developed with NEOTOMA (https://www.neotomadb.org/) and PANGAEA (https://pangaea.de/) databases.

These new datasets benefit from improved dating techniques and age modelling methods. The result of which is that newly acquired pollen series have reduced temporal uncertainty and improved resolution, allowing to more precision in interpretation of local and regional ecosystem dynamics and climate-vegetation interactions. All this allows to envisage new scientific developments of which one can cite three examples here:

### 2.3.1 Better understanding of ecosystem-human interactions

The identification and quantification of human-induced alterations to the Earth's surface are critical to understand the role of land-use change on ecosystems and climate. The Land Cover 6k (6000 yrs BP) project of IGBP PAGES (http://www.pastglobalchanges.org/science/wg/landcover6k) described in Gaillard *et al.* (2018) is a unique opportunity to develop a methodological approach to carefully reconstruct land cover change from pollen data and evaluate anthropogenic land-cover change scenarios for palaeoclimate modelling. The major limitation of such a quantification in tropical Africa is that ‘with very few exceptions, tropical trees have zoophilous pollinating systems and relatively low pollen productivity’ (Ritchie 1995; p. 487). The relationship between pollen percentages in diagrams and actual vegetation cover is thus extremely difficult to assess. Within the equatorial forest for instance, many tree taxa are under-represented or even absent from the pollen assemblages.

The reliability of any landscape reconstruction requires the spatial scale represented by the pollen assemblage to be carefully taken into account. This requires the most accurate possible
evaluation of pollen productivity of species and pollen-rain settling time. Following the work of Duffin and Bunting (2008) in South Africa, Gaillard and colleagues are currently applying the LOVE (Local Vegetation Estimates) and REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) models developed by Sugita (2007a,b) in Central Africa. The development of such an approach as well as the compilation of pollen and archaeological data (Marchant *et al.* 2018) can greatly improve the involvement of the palynological community in the study of land-use as a climate forcing.

### 2.3.2 Improved constraint of climate variability over the last millennia

The recent publication of Nash *et al.* (2016) within the framework of the PAGES 2ka working group (http://www.pastglobalchanges.org/science/wg/2k-network) showed that Africa is one of the world's most poorly documented regions in terms of climate reconstructions over the last millennia. Historical archives are very rare, as are natural archives with adequate temporal resolution and age control. Time frames where historical records overlap the prehistorical data are important to obtain seamless reconstructions and validate reconstructions. Improving the spatial coverage and resolution of palaeoecological records is crucial for studying natural decadal (or multi-decadal) climate variability and associated mechanisms. It is also essential to analyze the complexity of spatial hydroclimate patterns, such as that suggested for the Little Ice Age (1250–1750 CE) in Africa, for which wet or dry regions have been identified.

### 2.3.3 Understanding vegetation responses to abrupt climate change

The evolution of northern Africa from a 'Green Sahara' state to one of the most arid deserts today (Kröpelin *et al.* 2008) or the collapse of the equatorial forests (e.g., Lézine *et al.* 2013) occurred at the end of the African Humid Period. These are among the most emblematic examples of the extreme changes that can affect the global environment with dramatic consequences for human populations. The tipping points and climatic drivers between extreme states remain to be studied, as do the early warning signals of these environmental crises, which may date back several millennia, and still need to be identified. Long-term, high-resolution and evenly distributed pollen records are critical to address these questions.

## 2.4 CONCLUSION

The African Pollen Database aims at providing the scientific community, students and teachers with scientific and educational tools (pollen grain determination tools, modern and fossil data duly validated and dated, publications) to address key issues for understanding the vulnerability of ecosystems facing climate change. It ensures interoperability with international databases for multi-proxy reconstructions of the past environment. Beyond these activities, the African Pollen Database is a scientific network to develop the sharing of data and knowledge between researchers in different countries.

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CHAPTER 3

Preliminary evidence for green, brown and black
worlds in tropical western Africa during the
Middle and Late Pleistocene

William D. Gosling, Crystal N.H. McMichael, Zoë Groenewoud & Eleonora Roding

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

Charlotte S. Miller

*Leeds Trinity University, Leeds, United Kingdom*

Adele C.M. Julier

*Plant Conservation Unit, University of Cape Town, Cape Town, South Africa*

ABSTRACT: Modern ecological studies indicate that the degree of openness in African vegetation cover is determined, in part, by the presence of herbivores and fire as consumers of vegetation. Where herbivores are the dominant consumer of vegetation the resultant open state is described as a 'brown' world. Where fire is the dominant consumer of vegetation the resultant open state is described as a 'black' world. While if neither consumer is dominant then a more closed canopy states arises that is described as a 'green' world. Here we use palaeoecological data obtained from Lake Bosumtwi (Ghana) to characterize green, brown, and black worlds during two short sections of around 1000 years each, deposited around 200,000 and 100,000 years ago (Middle and Late Pleistocene). We characterize the vegetation cover using pollen and phytoliths, herbivory using *Sporormiella* and fire using micro-charcoal. We find that during c. 1000 years of the Middle Pleistocene fire was the major consumer of vegetation, while during c. 1000 years in the Late Pleistocene herbivores were relatively more important consumers of vegetation. We therefore suggest that the Middle Pleistocene section represents a black world, while in the Late Pleistocene section we capture a combination of green, brown and black worlds. The duration of these states seems to range from centuries to millennia and transitions are observed to occur in both an abrupt and a stepwise fashion. These preliminary data demonstrate how palaeoecological information can be used to gain insights into past landscape scale processes over thousands of years. Further work is required to test the robustness of these findings and to provide a higher temporal resolution to aid the link with modern ecological studies.
## 3.1 INTRODUCTION

The theory of ‘alternative stable states’ proposes that biotic and abiotic feedbacks can determine the composition and structure of an ecosystem regardless of external factors, such as climate (May 1977; Scheffer et al. 2001). The presence of herbivory and fire activity in African landscapes has long been suggested to be a key factor in determining the openness of the vegetation cover (Stebbing 1937). To characterize the role of herbivory and fire as mechanisms determining the degree of vegetation openness (alternative stable state) William Bond developed the concept of ‘green’, ‘brown’ and ‘black’ worlds (Figure 1; Bond 2005; Bond 2019). This ‘multi-coloured’ world model comprises three vegetation states based on differences in herbivory and fire as consumers of vegetation: (i) a ‘green’ world where consumers (herbivores and fires) are at sufficiently low occurrence levels as to not influence vegetation growth and consequently vegetation cover is more closed and primarily controlled by plant resource acquisition, (ii) a ‘brown’ world where an abundance of herbivores consuming seeds, seedlings and saplings means a more open vegetation structure, and (iii) a ‘black’ world where the frequent occurrence of fires consuming vegetation means a more open vegetation structure.

Modern studies in African savannas have demonstrated that herbivory and fire play an important role in the complex interactions that determine vegetation openness (Sankaran et al. 2008) and consequently the regulation of both are routinely used in landscape management (Roques et al. 2001). Evidence from modern exclosure experiments has demonstrated that the removal of animals from ecosystems can result in changes to vegetation state on timescales of years to decades (e.g. Riginos et al. 2012; Staver et al. 2009). While the manipulation of fire regimes, through experimental burns and fire suppression initiatives, have demonstrated vegetation state can also be altered through these processes on decadal timescales (e.g. Enslin et al. 2000; King et al. 1997). Over the longer-term (>100s of years) palaeoecological data have revealed that past changes in herbivory and fire activity have altered African vegetation composition and structure (e.g. Ivory and Russell 2016; Runcia et al. 2009; Shanahan et al. 2016). Palaeoecological data therefore provide an opportunity to search for evidence of the green, brown and black worlds proposed by Bond (2005), test the timescales of their stability, and discover how transitions between them occur.

Based on Bond's multi-coloured world model it can be suggested that the addition, or subtraction, of either herbivory or fire as a consumer of vegetation in a landscape would result in a shift in the degree of openness (Figure 1). Here we use palaeoecological data to parametrize vegetation openness (Poaceae pollen/phytoliths), herbivory (Sporormiella) and fire (charcoal) to provide ‘snap shots’ of vegetation states in tropical western Africa during the Middle and Late Pleistocene. We use these data to identify periods of time when consumers (both animals and fires) did, and did not, exert a dominant control over the vegetation openness.

<figure><img src="image_10.png" /><figcaption>**Figure 1.** Conceptual panorama of vegetation change across an African landscape dependent on the dominant consumer of vegetation. Green = absence of consumers. Brown = herbivores are the dominant consumers. Black = fire is the dominant consumer.</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>**Figure 2.** Major vegetation types of western Africa relative to Lake Bosumtwi (Ghana). Vegetation classifications follow White (1983).</figcaption></figure>

## 3.2 MATERIALS AND METHODS

### 3.2.1 Study site

Lake Bosumtwi (06° 30′ 06.04″ N, 01° 24′ 52.14″ W, 97 metres above sea level; Figure 2) was formed by a meteorite impact *c*. 1 million years ago and is a hydrologically closed system (Koeberl *et al.* 1998). The International Continental Scientific Drilling Program (ICDP) Lake Bosumtwi drilling project extracted a *c*. 295 m sediment core from the centre of the basin in 2004 (named BOS04-5B) (Koeberl *et al.* 2005; Koeberl *et al.* 2007).

Lake Bosumtwi lies within the seasonal migration path of the Intertropical Convergence Zone (ITCZ) and moisture is also delivered to the site by the West African monsoon (Nicholson 2009). This climate configuration results in a strong gradient of decreasing precipitation from south to north across western Africa. Concomitant with the climate gradient is a vegetation gradient which means that today Lake Bosumtwi is surrounded by semi-deciduous forest, with evergreen forest to the south, and savanna to the north (Figure 2; White 1983). Analysis of ancient pollen contained within the BOS04-5B core revealed multiple transitions between forest and savanna vegetation during the last *c*. 520,000 years which have been linked to multi-millennial, orbitally forced, climate changes (Miller and Gosling 2014; Miller *et al.* 2016). In this study, two short (*c*. 5 m) sections of the core, in which vegetation transitions had previously been identified, were sub-sampled for further palaeoecological analysis to explore the impact of shorter-term landscape-scale process on past vegetation dynamics (Figure 3; Gosling *et al.* 2021).

### 3.2.2 Chronological control

Previously published radiometric dates indicate that the meteorite which formed Lake Bosumtwi impacted the Earth *c*. 1.07 ± 0.05 million years ago (Koeberl *et al.* 1998). Subsequent sediment
<figure><img src="image_12.png" /><figcaption>**Figure 3.** Position of the two sections focused on in this study (grey bars) from Lake Bosumtwi relative to previous palaeoecological work (modified from Miller *et al.* 2016).</figcaption></figure>

accumulation through the core has been constrained by radiocarbon, U-series and optically stimulated luminance dating (Shanahan *et al.* 2013a). The two sections of the BOS04-5B core focused on here were recovered from 61.25–56.05 and 38.85–33.45 metres below lake floor (mblf) (Figure 3). Based on the radiometric dating these two sections were likely deposited during the Middle Pleistocene (c. 200,000 years ago) and Late Pleistocene (c. 100,000 years ago) respectively (Miller *et al.* 2016).

Previous studies into sediment deposition within Lake Bosumtwi indicated that the light-
dark couplets of laminations within the sediments likely represent seasonal cycles (Shanahan
*et al.* 2013b). Therefore, to gain a minimum estimate of the timescale over which these sections
were deposited, the number of laminations within each section was counted on the basis that the
sediment core images were included in the initial core descriptions.
### 3.2.3 Palaeoecological analysis

Twenty sub-samples were prepared for palaeoecological analysis across each of the two sections using standard techniques including density separation, acetolysis and sieving at 180 µm (Moore et al. 1991). An exotic marker (*Lycopodium*) was added to each sample to allow the concentration of microscopic remains to be calculated (Stockmarr 1971); University of Lund, batch #483216, containing 18,583 grains ± 4.1%. Each sub-sample was analysed for the concentration of Poaceae pollen, *Sporormiella*, and micro-charcoal (< 180 µm); identifications followed Gosling et al. (2013), van Geel and Aptroot (2006), and Whitlock and Larsen (2001) respectively. Phytoliths were also present in the prepared slides. Phytolith concentration from the same sub-samples were analysed across the Middle Pleistocene section; phytolith identifications were based on Piperno (2006).

### 3.2.4 Statistical analysis and data presentation

To assess the robustness of the palaeoecological datasets 95% confidence intervals were calculated (following Maher 1981). Bayesian Change Point (BCP) analysis (Barry and Hartigan 1993), which determines if there is a significant change in the mean of the variable at a given point in a time series, was used on: (i) *Sporormiella* (herbivore) concentration, and (ii) micro-charcoal (fire) concentration data. The posterior probabilities of the BCP analysis indicated the likelihood of significant change of those variables at each time step sampled (Barry and Hartigan 1993; Blois et al. 2011). Where the posterior probability of the BCP analysis exceeded 0.8 for *Sporormiella* or charcoal, a zone boundary was defined, indicating a significant change in herbivory or fire activity. Data were plotted using C2 (Juggins 2005).

## 3.3 RESULTS

Previously published radiometric dating indicates that the two sections studied here were deposited during the Middle and Late Pleistocene (Figure 3; Shanahan *et al.* 2013a). The results of the younger section are presented in the upper panel (Figure 4A) and the results of the older section are presented in the lower panel (Figure 4B).

### 3.3.1 Lamination counting

Approximately 1200 light-dark couplets of laminations were identified in the Middle Pleistocene section; however, no laminations could be identified in three parts of the section at: 60.25–59.85, 58.65–58.45, and 57.05–56.85 mblf (Figure 4B). Approximately 750 light-dark couplets of laminations were identified for the Late Pleistocene section; however, no laminations could be identified between 34.45 and 33.45 mblf (Figure 4A).

### 3.3.2 Palaeoecological analysis

For the Middle Pleistocene section two abrupt changes in vegetation consuming processes were detected by the BCP analysis at 59.25 (micro-charcoal) and 56.65 (*Sporormiella*) mblf defining three zones (Zones i, ii, and iii; Figure 4B). Within Zone i Poaceae pollen occurs in high concentrations (mean of 38,000 grains/cm³), Poaceae phytoliths, tree phytoliths and micro-charcoal are ever present but are highly variable in concentration (1100–46,000 Poaceae phytoliths/cm³, 28,000–240,000 tree phytoliths/cm³, and 250,000–1,600,000 fragments/cm³),
and *Sporormiella* is absent. In Zone ii Poaceae pollen is continually present at medium con-
centration (mean 26,000 grains/cm³), Poaceae phytoliths, tree phytoliths and micro-charcoal are
usually present and highly variable in concentration (4000–127,000 Poaceae phytoliths/cm³, 0–
360,000 tree phytoliths/cm3, 199,000–6,194,000 fragments/cm³), and *Sporormiella* is absent. In
Zone iii Poaceae pollen and phytoliths occur at high concentrations (mean 35,000 grains/cm³
and 34,000 phytoliths/cm³ respectively), but tree phytoliths are absent; micro-charcoal is vari-
able (395,000–978,000 fragments/cm³), and *Sporormiella* is continually present (395–1133
spores/cm³).

For the Late Pleistocene section two abrupt changes in vegetation consuming processes
were detected by the BCP analysis at 36.45 (*Sporormiella* and micro-charcoal) and 34.25
(*Sporormiella*) mblf defining three zones (Zones I, II, and III; Figure 4A). Within Zone I Poaceae
pollen (17,000 grains/cm³), *Sporormiella* (mean 1200 spores/cm³), and micro-charcoal (mean
291,000 particles/cm³) are all relatively highly abundant within the section. In Zone II Poaceae
pollen (mean 14,000 grains/cm³) are abundant, while *Sporormiella* and micro-charcoal vary
widely (0–8400 spores/cm³ and 15,000-496,000 fragments/cm³ respectively). In Zone III Poaceae
pollen (mean 2700 grains/cm³) and micro-charcoal (mean 4400 fragments/cm³) are relatively
low, while *Sporormiella* varies (0–4000 spores/cm³) in concentration.

**3.4 DISCUSSION**

**3.4.1 Timescales of deposition**

Radiometric dating indicates that the Middle Pleistocene section was deposited *c.* 200,000 years ago during a period of high eccentricity in the Earth's orbital cycle (Miller *et al.* 2016). This orbital configuration of northern hemisphere insolation maximum, during a precession minimum and an eccentricity maximum, extenuates seasonal variations at Lake Bosumtwi (6°N). Therefore, this period of time likely represents ecosystem functioning under high seasonal stress, and a consistently low level of Lake Bosumtwi during this period (Figure 2). The Late Pleistocene section is indicated to have been deposited *c.* 100,000 years ago as part of the longer transition out of the last interglacial period and includes a period of relatively higher lake levels (Figure 2).

Lamination counting within the two sections revealed 1200 light-dark couplets in 5.2 m of sediment in the Middle Pleistocene section, and 750 light-dark couplets in 5.4 m in the Late Pleistocene section. These counts were derived from visual inspection of digital core scan images and consequently likely represent an under-estimate of the true number of bands present because some may not have been captured in the digital imagery of the core surface. To reveal all bands, and develop a robust internal chronology, further analysis of the sediments in thin section is required. The preliminary analysis presented here shows this is a promising line of investigation and, based on the visible bands, it can be roughly estimated that the period of deposition represented by each of these sections is more than 1000 years. The relatively higher number of bands in the older section could be related to the enhanced seasonality and lower sedimentation rates during this period.

**3.4.2 Evidence for green, brown and black worlds**

Fire (charcoal) was ever present, and highly abundant, in the Middle Pleistocene section (Zone i, ii and iii in Figure 4B), while herbivores (*Sporormiella*) only appear in the uppermost samples (Zone iii in Figure 4B). The first transition (Zone i to Zone ii) is defined by a change in fire activity that is coincident with a slight drop in the average concentration of Poaceae pollen, however, no directional change in the concentration of Poaceae or tree phytoliths is discernible at this time. This suggests that vegetation state did not change significantly. The second transition
<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

**Figure 4.** Palaeoecological diagram from two portions of the Lake Bosumtwi (BOS05-3B) sedimentary record: (A) Late Pleistocene (c. 39.0–33.0 mblf), and (B) Middle Pleistocene (c. 56.0–61.5 mblf). Dark grey plus symbols indicate upper and lower confidence intervals (95%). Horizontal light grey bands indicate portions of the sediment without laminations. For 'Abrupt change' curves: black dotted line indicates BCP analysis of *Sporormiella* concentration data, black dashed line indicates BCP analysis of micro-charcoal concentration data, vertical solid grey line indicates 0.8 significance threshold. In the case of one sample, at 59.25 mblf, the concentration of charcoal fragments exceeds the scales shown and the upper value is indicated numerically. Raw data available from Gosling *et al.* (2021).
(Zone ii to Zone iii) is defined by the appearance of herbivores, and is associated with the loss of tree phytoliths and the rise of Poaceae pollen and phytolith concentrations. This suggests that increased herbivory did diminish, or alter, the woody component of the vegetation. Throughout this section the high concentration of Poaceae (indicated by both pollen and phytoliths) with a variable woody component (indicated by the tree phytoliths) suggests that the landscape around Lake Bosumtwi during this short snapshot of the Middle Pleistocene was similar to the open vegetation found in the forest-savannah transition zone c. 250 km north of Lake Bosumtwi today (Julier et al. 2018), rather than the closed vegetation found close to the site today (Julier et al. 2019; Figure 1). Today in the transition zone fires during the dry season (November-March) limit juvenile establishment and sapling recruitment (Armani et al. 2018). The enhanced seasonality during this part of the Middle Pleistocene likely resulted in two prolonged and intense dry seasons during which burning could have occurred. The enhanced seasonality likely meant that fire was an even greater consumer of vegetation than it is today in the transition zone, suggesting that this entire section likely represents ‘black’ world open vegetation.

Fire activity and herbivory both change through the Late Pleistocene section (Figure 4A). The first transition (Zone I to II) sees first a spike and then a persistent decline in both herbivory and fire activity. Prior to the spike (Zone I) herbivory levels and fire activity are relatively high and stable, and this is mirrored in the Poaceae concentration. After the spike (Zone II) herbivory and fire activity fluctuate, and are periodically absent, which is coincident with a slight drop in Poaceae concentration. *Sporormiella* and micro-charcoal concentrations relative to the Middle Pleistocene ‘black’ world section are higher and lower respectively. This suggests that in the Late Pleistocene section herbivores likely played a relatively more important role in determining vegetation structure. Therefore, it can be tentatively suggested that where *Sporormiella* is abundant a ‘brown’ world persisted. Although it should be noted that both herbivory and fires were clearly present and no doubt both helped to maintain the vegetation openness. Furthermore, it seems that the role of both herbivory and fire as consumers of vegetation (promoting higher Poaceae concentration and inferred openness) is diminishing through Zones I and II. The concomitant decline in consumers and Poaceae perhaps suggests a move from a consumer controlled stable state, towards a more closed canopy ‘green(er)’ world. The second transition (Zone II to III) is defined by a rise in herbivory, and is coincident with a drop (to near absence) in fire activity, low concentrations of Poaceae pollen, a sedimentological change (loss of laminations), and a drop in lake level (Figure 2). It is consequently unclear if the lower Poaceae pollen concentration (and inferred decreased openness) observed in Zone III are a direct result of diminishing numbers of herbivores and fire activity leading us into a ‘green’ world, or if other, possibly climatological or taphonomic controls are responsible.

### 3.4.3 Insights into past vegetation states in tropical western Africa

The preliminary data from the two sections examined here provide evidence for the presence of, and switches between, green, brown and black worlds in tropical western Africa during the Middle and Late Pleistocene. It is also apparent that different combinations of herbivores and fire in the landscape resulted in different degrees of openness (stable states) persisting. It seems likely that the background climatic configuration and seasonality played a significant role in determining the relative importance of these processes; an observation that aligns with modern studies which indicate that fire prevalence is most strongly linked to previous years’ rainfall (van Wilgen et al. 2004). The presence of both herbivores and fire within the landscape is coincident with elevated concentration of Poaceae pollen and phytoliths in line with expectations from modern studies that suggest these vegetation consumers promote more open ecosystems (Bond 2005; Bond 2019; Warman and Moles 2009). The timescales over which the green, brown and black alternative ‘stable states’ persisted appears to be at least on the order of centuries to millennia.
It can be tentatively suggested that transitions between green, brown and black worlds occur over decades to centuries; however, it should also be noted that both gradual transitions seem to exist (i.e. in the Late Pleistocene section herbivory, fire activity and Poaceae all decline in a step wise fashion) as well as abrupt shifts (i.e. in the Middle Pleistocene section herbivory appears and tree phytoliths disappear at the same time). The different modes of transition suggest a complex series of interactions are responsible for initiating and driving vegetation dynamics during both time windows. This finding is in line with more recent data from savanna in eastern African that suggest that over the last 1400 years periodic fluctuations in woody cover driven by landscape processes are the rule, not the exception (Gillson 2004). Complex landscape scale processes have also been observed to be important over longer timescales during the transition out of the last interglacial period at Lake Bosumtwi (Shanahan et al. 2016) and over shorter timescales in the modern forest-savanna transition zone to the north (Ametsitsi et al. 2020). These findings emphasize the need for further empirical data to contextualize the role of processes, such as herbivory and fire activity, in determining vegetation states in Africa across space and through time.

### 3.4.4 Future perspectives

To determine the relative importance of herbivory and fire as consumers of vegetation, and how this changes through time, at Lake Bosumtwi further research is required. Firstly, a robust internal chronology should be established through detailed examination of the nature and frequency of the laminations, and secondly further details should be extracted from the palaeoecological and palaeoclimatic record. Specifically, detailed pollen and phytolith analyses are required at a higher temporal resolution to characterize trajectories of vegetation change. These vegetation data need to be supported by: (i) further charcoal analyses (micro- and macro-charcoal and charcoal chemistry) to reveal the biomass consumption and temperature of burning (Gosling et al. 2019; Whitlock and Larsen 2001), (ii) examination of a full suite of coprophilous fungal spores (not just *Sporormiella*) to provide insights into changing animal assemblages (Loughlin et al. 2018; van Geel and Aptroot 2006), and (iii) further independent evidence for climatic change should be sought, including further $\delta^{15}N$ analysis to determine changes in moisture balance (Talbot 2001; Talbot and Johannessen 1992), and pollen chemical analysis to identify fluctuations in solar irradiance (Jardine et al. 2016; Jardine et al. 2021).

## 3.5 CONCLUSIONS

The examination of Middle and Late Pleistocene sections of the Lake Bosumtwi sediment core provide evidence for, and switches between, 'green', 'brown' and 'black' worlds. The different coloured worlds (alternative stable states) each seem to persist for hundreds to thousands of years. The addition, and subtraction, of herbivory and fire activity from the landscape around Lake Bosumtwi seems to have resulted in vegetation change occurring in both an abrupt and complex gradual fashion over decades to centuries. Although the mechanisms behind the changes in herbivory and fire activity remain largely ambiguous, it seems likely that seasonality modulated by orbital forcing plays a strong role in governing fire activity. To further our understanding of the persistence of, and transition between, alternative stable states around Lake Bosumtwi we now need to improve the chronological control, enhance our sampling resolution, and expand the range of proxies analysed to provide a comprehensive insight into past ecosystem dynamics. Armed with these data we will be able to better anticipate the impact of projected climate changes for tropical western Africa.
## ACKNOWLEDGEMENTS

Palaeoecological data were generated by ZG and ER as part of their BSc Biology dissertation projects supervised by WDG and CNHM. CSM and AJ assisted with the pollen identifications. WG wrote the manuscript with contributions from all authors.

## DATA AVALIABILITY

All data presented in this manuscript can be downloaded from DOI: 10.6084/m9.fishshare.12738131

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<figure><img src="image_15.png" /></figure>

Taylor & Francis

Taylor & Francis Group

http://taylorandfrancis.com
CHAPTER 4

Holocene high-altitude vegetation dynamics on
Emi Koussi, Tibesti Mountains (Chad, Central
Sahara)

Michèle Dinies<fnref n="1" />, Lena Schimmel & Philipp Hoelzmann

Freie Universität Berlin, Institute of Geographical Sciences, Berlin, Germany

Stefan Kröpelin

University of Cologne, Institute of Prehistoric Archaeology, Africa Research Unit, Cologne, Germany

Frank Darius

Technische Universität Berlin, Institute for Ecology, Berlin, Germany

Reinder Neef

German Archaeological Institute (DAI), Scientific Department of the Head Office, Berlin, Germany

ABSTRACT: High mountains are sensitive to climate change. Holocene lake remnants witness to the last Saharan Humid Period (SHP) in the Tibesti, the highest mountains of the Sahara (>3000 m asl). The impact of Holocene climatic change on the terrestrial montane ecosystems, however, is largely unknown. Palynological investigations on a palaeolake sequence from the summit caldera of the Emi Koussi, the highest volcanic complex of the Central Sahara, were performed to address this issue. Based on charred plant particle concentrations, the age depth model indicates a Holocene age of the palaeolake (c. 9500-5500 cal yr BP). Shifts in the vegetation composition indicate altered climatic conditions: high proportions of Poaceae and fern as well as highly fluctuating *Artemisia* frequencies characterize the SHP, strongly dominating *Ephedra distachya*-type proportions reflect the present vegetation, evidencing distinctly decreased humidity. The missing mass expansion of tropical tree taxa into the summit zone meanwhile points to persisting low temperatures during the Holocene. The absence of Mediterranean tree taxa during the SHP indicates that migration from the Mediterranean to the southern Sahara was not possible. Hence, a survival of Mediterranean tree taxa within micro-refugia may also be excluded. An exception is *Erica (arborea)* which expanded only during the Middle Holocene, relying on relict populations. Increased precipitation at persisting lower temperatures thus shaped the

<footnote n="1">¹Other affiliation: German Archaeological Institute (DAI), Scientific Department of the Head Office, Berlin, Germany</footnote>
high altitudinal ecosystems during the SHP, triggering modifications in the vegetation composition. The ecosystem type itself, a montane steppe, remained. This is in clear contrast to the contemporaneous marked biome changes in the surrounding Saharan plains.

## 4.1 INTRODUCTION

Due to their positions amidst today's largest hot desert, the mountain complexes Hoggar and Tibesti in the central Sahara are exceptional regions, resembling islands of increased biodiversity. Even though the altitudinal change in precipitation and temperature leads to more mesic conditions at higher elevations, there is no montane tree belt in these Central Saharan massifs, distinguishing them from the tropical mountains in East Africa as well as from the Mediterranean mountain ranges in the north. A combination of aridity and low temperatures is claimed to prevent major tree growth in the Hoggar and Tibesti, fostering at their summit a vegetation formation dominated by species of the genera *Ephedra*, *Artemisia* and *Pentzia*, called 'pseudo-steppe' or 'steppe culminale' (e.g. Maire and Monod 1950; Messerli and Winiger 1992; Ozenda 1991; Quézel 1965). The steppe culminale fits the criteria of paleartic steppes characterized by (a) the dominance of herbs, mainly grasses with high chamaephyt proportions in some regions (b) more than 10% vegetation cover (c) occurring in climates too dry for taller woody vegetation and at least occasionally affected by frost (Wesche et al. 2016). This definition thus includes the naturally occurring grasslands of the Mediterranean and of the subtropical-tropical arid zones as steppe, similar to the definition of Le Houérou (2001, 2009).

Because of the strong dominance of chamaephyts, the steppe culminale of the Tibesti may be assigned to the desert steppes, characterized by vegetation cover of only 10–25% with often increased dwarf shrub proportions, a vegetation formation mediating to subtropical deserts (cf. Wesche et al. 2016). The present heterogenous biogeographical composition of the Central Saharan montane ecosystems points to multiple floristic relations: inner Saharan, Sahelian, Afroalpine East African, and links to the Mediterranean phytoregion. The latter are documented by Mediterranean woody plants at altitudes higher than 1500 m asl (*Cupressus dupreziana*, *Erica arborea*, *Olea europaea* subsp. *laperrinei* and *Rhus tripartite*) and numerous annuals and perennials. However, most of these woody taxa only occur in the Hoggar mountains, compliant with higher proportions of Mediterranean dwarf shrubs and annuals. The more northerly position of the Hoggar massif in comparison to the Tibesti and thus (closer) proximity to the Mediterranean phytoregion accounts for this difference (Maire 1935; Maire and Monod 1950; Médail and Quézel 2018; Ozenda 1991; Quézel 1965).

As to the African Humid Period, several dated palynological and anthracological investigations in the surrounding plains of the Eastern and Central Sahara provide evidence of profound ecosystem changes, with tropical plant taxa migrating some 500 km northwards compared to their present day distribution, thus as far north as the Tibesti or even further north (Gabriel 1977; Haynes et al. 1989; Hély and Lézine 2014; Jahns 1995; Lézine 2017; Maley 1981; Ritchie et al. 1985; Ritchie 1987; Ritchie 1994; Ritchie and Haynes 1987; Schulz 1987, 1991; Schulz 1991; Mercuri et al. 1998; Mercuri 1999; Mercuri and Grandi 2001; Neumann 1989; Trevisan et al. 1998; Watrin et al. 2009). There is, however, no clear evidence of a similar distinct southward migration of Mediterranean plant taxa into the Central Saharan plains during the Holocene.

An intensified and northwards expanded summer monsoon is supposed to be the main humidity source (Kutzbach 1981). Other atmospheric patterns are assumed to have contributed as well, such as e.g. seasonal tropical plumes and extratropical troughs (Dallmeyer et al. 2020; Knippertz 2005; Maley 2000; Skinner and Poulsen 2016), and interactions of extratropic cyclones with the monsoonal system, either with or without overlaps (e.g. Baumhauer 2004; Rogerson et al. 2019) or with additional interferences of moisture from the Indian Ocean (Mercuri et al. 2018) are
discussed. Feedback mechanisms additionally seem to play a role. In models, interactive coupling between atmospheric and oceanic dynamics as well as land surface amplify the African monsoon (e.g. Braconnot et al. 1999, 2007; Claussen and Gayler 1997; Claussen et al. 1999; Kutzbach and Liu 1997; Pausata et al. 2016). The influence of land cover feedbacks is controversial (e.g. Braconnot et al. 1999 vs. Braconnot et al. 2007), however a positive feedback seems probable (e.g. Krinner et al. 2012).

Palaeolake remnants in the montane belt of the Tibesti and Hoggar massifs document the impact of increased precipitation during the African humid period (e.g. Jäkel and Geyh 1982; Maley 1981; Médail and Quézel 2018). The vegetation response however remains vague, because to date only single or few palynological samples scattered throughout the Central Saharan Mountains have been investigated, allowing only very punctual insights. Samples of the Hoggar tentatively dated to the beginning of the Pleistocene show high proportions of temperate and plant taxa, interpreted as relict woodlands of the Tertiary. During the Middle and Late Pleistocene, the proportions of tropical plant taxa as well as types representing the Saharan desert vegetation increased, while Mediterranean and temperate taxa persisted, however with decreasing importance. This led to the hypothesis that the desert vegetation established successively in the plains and thus acted as a barrier, isolating the mountain ranges, which however were connected by hydrogeographic networks activated during periods of increased humidity (Rossignol and Maley 1969). As to the African Humid Periods, the involvement of Mediterranean taxa in the Hoggar/Tassili and Tibesti mountain complexes remains ambiguous. Some authors suggest an expansion of Mediterranean or even temperate tree taxa in the Central Saharan mountains, while a re-investigation in the Hoggar and analyses on lake remnants in the Tibesti revealed only the few Mediterranean tree taxa still present today (e.g. Alimen et al. 1968; Gabriel 1977; Quézel 1958; Quézel 1965; Maley 1981; Maley 2000; Prentice et al. 2000; Medail and Quézel, 2018 versus Thinon et al. 1996 and own investigations).

Here, we present the first pollen diagram encompassing the period c. 9500-5500 cal yrs BP, based on palynological investigations of a ¹⁴C-dated sediment sequence from the deepest subcaldera of the highest volcanic shield complex, the Emi Koussi at about 3000 m asl. This analysis complements existing single sample investigations from various different geomorphological contexts. Relying on the new sequence, we will: a) present a chronology of the investigated lake remnant based on ¹⁴C-dates of organic material, b) indicate Holocene vegetation fluctuations at these highest altitudes and c) deduce climatic configurations from these vegetation reconstructions.

## 4.2 REGIONAL SETTING

### 4.2.1 Geomorphology

The Tibesti massif is one of the world's major and most significant examples of intracontinental volcanic provinces and covers more than 100,000 km² (Ball et al. 2019). Intense volcanic activity began as early as the Oligocene and intensified during the Quaternary (Deniel et al. 2015; Gourgaud and Vincent 2004). The Emi Koussi is the largest volcano of the entire Tibesti Volcanic Complex, with a basal diameter from 60 to 80 km and a summit caldera of 9–12 km in diameter. Altitude differences vary between c. 3000 m compared to the Bodélé depression in the south and c. 2300–2900 m to the Serir Tibesti in the north (Pachur and Altmann 2006). A succession of three volcanic sequences between 2.4 and 1.3 Ma formed the Emi Koussi volcano and each is related to the collapse of a caldera. Era Kohor is the youngest caldera that was formed during the last sequence (Gourgaud and Vincent 2004). Basalts overlaying Terminal Pleistocene to Holocene limnic sediments in the Emi Koussi caldera indicate volcanic eruptions until the recent past (Messerli 1972). Seismic activities are recorded even nowadays. Groundwater-coupled processes
like solfatars/fumaroles and hot springs are still active on the eastern slopes of Emi Koussi (Pachur and Altmann 2006).

4.2.2 Climate

In the plains surrounding the Tibesti, hot desert climates (BWh; Köppen 1918) prevail, whereas in the mountains the climatic conditions change due to the adiabatic lapse rate to cold desert climates (BWk) with mean annual temperatures below 18°C. Climate data are not available for the Emi Koussi, but some meteorological data from lower locations indicate the ‘classical’ precipitation increase and temperature decrease with increasing altitudes. Rainfall at the Trou au Natron at 2450 m asl, thus 1000 m below the sampled Emi Koussi lake remnant, amounts to an average annual precipitation of 93.3 mm and a mean annual temperature of 13.5° C (Gavrilovic 1969). The few data allowing vague insights into the distribution throughout the year indicate a precipitation maximum during May and another during August, with highest monthly means during July (Maire and Monod 1950). For the highest altitudes of the Emi Koussi, precipitation estimations based on single measurements and deduced from altitude, geomorphology and vegetation range from 50 to 150 mm per year (Wininger 1972, Figure 1, Vegetation map). In contrast to the lower mountains and plains that are mainly affected by monsoonal summer precipitation, the high altitudes seem to profit from orographic, frequent but minor precipitations. Coupled with clouds, this effective moisture source propagates plant growth (Quézel 1958).

<figure><img src="image_16.png" /></figure>

**Figure 1.** Satellite image (Esri World Imagery) of the Tibesti massif and its surrounding plains, Central Sahara. Inlet map: Schematic map of the vegetation zones (centres of endemism: III – Sudanian, VII – Mediterranean, and the regional transition zones: XI – Guinea-Congolia/Sudania, XVI – Sahel, XVII – Sahara, XVIII – Mediterranean/Sahara), following White (1983). The reconstructed northern limits of Sudanian and Sahelian plant taxa during the SHP are indicated as green lines (Neumann 1989; Schulz 1991). Isohyetes (in grey) are from Railsback *et al.* (2016).
### 4.2.3 Today's vegetation of the Tibesti

After Maire and Monod (1950), Quézel (1958), Ozenda (1991) and Médail and Quézel (2018), three main altitudinal belts can be distinguished in the Tibesti and Hoggar Mountains: a Saharan-Tropical belt similar to the contracted vegetation surrounding the mountains, followed by a montane Saharan-Mediterranean belt with increasingly diffuse plant cover, and a summit zone. The generalized vegetation map after Quézel (1958, 1964, 1965) shows this altitudinal controlled vegetation distribution on the Emi Koussi volcano itself (Figure 2).

(1) Saharan-Tropical desert vegetation of the plains: contracted desert vegetation with *Panicum turgidum* and *Acacia ehrenbergiana* dominates.

(2) Saharan-Tropical belt up to c. 1700 m asl: the vegetation resembles the desert vegetation of the surrounding plains, with Sahelian plant taxa such as acacias (*A. tortilis* var. *raddiana*, *A. laeta*, *A. stenocarpa*), Maerua crassifolia and Capparis decidua in the wadis, and *Hyphaene thebaica* and *Salvadora persica* bordering them. Together with a grassy vegetation formation in depressions or runnels (*Aristidia funiculata* - *Indigofera sessiliflora* formation), they are supposed to represent remnants of plant formations that expanded northwards during the African Humid Period (Médail and Quézel 2018).

(3a) Lower montane zone of the Saharan-Mediterranean belt, c. 1700-2500 m asl: in this zone the Sahelian vegetation fades out, and the plant cover becomes increasingly diffuse. *Acacia stenocarpa* and *A. laeta*, different *Ficus* species, *Grewia tenax*, *Rhus*, *Capparis spinosa* and *Boscia salicifolia* grow in the wadis. Montane *Aristida* grasslands (3b1) cover the surfaces between the wadis, with *Linaria* and *Helianthemum* as characteristic taxa. The two *Acacia* species form the upper tree line at altitudes of 1800-2300 m asl, depending on the exposition, while dwarf grown acacias may even reach 200 m higher (Messerli 1972; Quézel 1965). As to the Sahelian affinity of the acacias, temperature is claimed as the limiting factor for tree growth. Yet, aridity seems to be a relevant factor as well: in the Hoggar mountains relict stands of *Olea europaea* subsp. *laperrinei* trees grow in caves at 2700 m asl, and at the Emi Koussi *Erica arborea* grows in ravines between 2500 and 3000 m asl, indicating that theoretically these Mediterranean trees should constitute the upper timber line at higher altitudes or even cover the highest summit. Quézel (1965) thus assumed that these and other Mediterranean (and Temperate) elements disappeared 4000-5000 years ago as a result of aridification.

(3b) Upper montane zone of the Saharan-Mediterranean belt (steppe culminale), above c. 2500 m asl: dwarf shrubs prevail at these highest altitudes. While in the Hoggar mountains *Artemisia herba-alba* (*Seriphidium herba-alba* (Asso) Sojak), *Artemisia campestris* (subsp. *glutinosa* (Besser) Blatt.), *Ephedra major* Host and *Pentzia monodiana* Maire form these summit steppes, endemic counterparts, *Artemisia tilhoana* Quézel and *Ephedra tilhoana* Maire, replace them, with *Pentzia monodiana*, *Ballota hirsuta* and *Lotus tibeticus* accompanying them as characteristic species. *Euphorbia granulata*, *Erodium oreophilum*, *Campanula bordesiana*, *Helianthemum lippi* and *Helichrysum monodianum* are also common in these steppes. This is supposed to represent a vegetation formation with a long-lasting Quaternary history (Quézel 1958, 1965).

## 4.3 MATERIALS AND METHODS

### 4.3.1 Sampling

Within the Era Kohor caldera, palaeolake remnants are preserved at the NW slopes, covered by volcanic talus material (Figures 2 and 3). These diatomaceous sediments exhibit a thickness of 145 cm and were sampled at an altitude of 2796 m asl (top of the sampled sequence;
<figure><img src="image_17.png" /><figcaption>**Figure 2.** a) Digital elevation model (DEM) of the Emi Koussi shield volcanic complex with the three summit calderas after Gourgand and Vincent (2004) and the generalized vegetation zones after Quezel (1958; 1964; 1965) and Maire and Monod (1935, 1950). b) DEM of the Era Kohor caldera with the position of section W566 c) NW-SE profile across the Era Kohor caldera.</figcaption></figure>

19° 50.376' N, 18° 33.177' E), some 130 m above the present crater floor. The desiccated sediments (diatomite) were sampled in subsequent monoliths (W566-1 to W566-7; Figure 2). Sub-sampling of the monoliths was undertaken at 1 cm sample intervals where possible, after export of the monoliths to the laboratory. However, some monoliths did not reach the laboratory intact and for these segments a single bulk sample was taken.

### 4.3.2 Preparation of pollen samples and charred plant particles concentrates for ¹⁴C-dating

In a first step, samples at intervals of about 10 cm were prepared. Pollen preservation proved highly variable throughout the profile. Subsequently the intervals with pollen preservation were chosen for further palynological investigations. Samples were treated following common acid/base, heavy liquid and acetolysis protocols, thoroughly washing the samples with distilled water after each treatment (Eisele *et al.* 1994; Faegri and Iversen 1989; Moore *et al.* 1991;
Nakagawa *et al.* 1998). A volume of 10cm³ sediment (diatomite) was prepared, adding marker spores (Stockmarr 1971).

Pollen concentrations were prepared applying a combination of different protocols (Chester and Prior 2004; Brown *et al.* 1992; Regnéll and Everitt 1996; Nakagawa *et al.* 1998; Vandergoes and Prior 2003; Piotrowska *et al.* 2004) with the following preparation steps: (1) Treatment with ~10% HCl (heated), (2) Treatment with ~10% KOH (heated), (3) Dense-media separation with sodium-polytungstate (SPT; ~2.1 g/cm³), (4) Treatment with 12 M H₂SO₄ for 2 h, with 1.2 M H₂SO₄ for 3 h (heated), (5) Microscopic analysis of the residues to decide on the next steps for the processing procedure, (6) Density separation (1.6-1.2 g/cm³) with CsCl or repeated with 2.1 g/cm³ SPT, with microscopic control of the potential different phases, (7) Sieving (<6 µm).

Pollen slides were analysed using a transmitted light microscope (Leica DMRB) with 400–1000× magnification. Pollens were identified by using the reference collection of the DAI (Deutsches Archäologisches Institut, Berlin, Germany), electronic photographs of the African Pollen Database (downloaded in 2012, www://medias.obs-mip.fr/apd) and published pollen atlases (Bonnefille and Riotlet 1980; El-Ghazali 1993; Reille 1992).

## 4.4 RESULTS

### 4.4.1 Lithostratigraphy and radiocarbon dating of W566

The diatomite is faintly laminated in its entity, structured by oxidized bands, mainly ochre, some of them sustaining (Figure 3).

Six samples of the W566 sequence were radiocarbon dated (Table 1). The total carbon content of the diatomaceous sediments is generally extremely low and in consequence the datable amount of organic carbon in the prepared concentrates is also low. Macroscopic charred plant remains were not found in the sampled sequence. Thus, concentrates of microscopic charred plant particles were prepared for ¹⁴C-dating to enrich organic carbon for the necessary minimum mass of c. 0.1 mg to produce reliable ages. However, below 0.1 mg C uncertainty increases correspondingly (Kutschera 2016), in addition the risk of contamination during sample preparation rises with decreasing sample mass. The sample with only 0.04 mg C (Poz-12905) has been excluded from calculations of the age depth model because of the methodological uncertainties, as in other investigations (e.g. Parker *et al.* 2004). To establish an age depth model, rbacon, a Bayesian approach with an implemented outlier analysis was chosen (version 2.4.3; Blaauw and Christen 2011). The basal 10 cm were devoid of datable organic material, the ages for these 10 cm were thus extrapolated. With these first absolute datings of the diatomite of the Era Kohor caldera, we prove a Holocene age of the lake remnant.

### 4.4.2 Pollen sum and diagram

The pollen sum varies between 63 and 910, with 304 on average. It includes all terrestrial types as well as monolete fern spores. Ferns are supposed to have been common on terrestrial sites during the African Humid Period. Similarly, ferns were included in the main sum in earlier investigations in the Tibesti (Maley 1981) and in Yemen (Lézine *et al.* 2007). Aquatics and other spores are excluded. The pollen sum strongly depends on the pollen concentration and preservation of the respective sample: very low pollen concentrations and/or higher proportions of corroded pollen resulted in part in low pollen sums. The diagram was drawn with Tilia (Grimm 2020). The pollen types are grouped according to their ecology in representatives of desert vegetation (of the plains), altitudinal steppes, thorn (and deciduous) savanna, and riparian and water vegetation.
<table><caption>**Table 1.** Radiocarbon dates from section W566 from the Era Kohor caldera. The ¹⁴C dates were calibrated with OxCal. The coverage of the different dated organic components is indicated as percentage values for each sample respectively.</caption><thead><tr><th>Lab-Nr.</th><th>Depth (cm) from top of W566</th><th>¹⁴C yrs BP</th><th>cal yrs BP (2sigma)</th><th>Material dated</th><th>mg C</th></tr></thead><tbody><tr><td>Beta441716</td><td>0–15</td><td>4720±30</td><td>5320–5580</td><td>90% charred plant particles, 10% tissues and pollen</td><td>no data</td></tr><tr><td>Poz122314</td><td>33–36</td><td>7480±50</td><td>8180–8380</td><td>90% charred plant particles, 10% probably limnic tissues</td><td>0.3</td></tr><tr><td>Poz122366</td><td>95–96</td><td>7700±40</td><td>8400–8590</td><td>85% charred plant particles; 10% minerogenic particles; 5% algae remains</td><td>0.8</td></tr><tr><td>Beta441715</td><td>123–125.5</td><td>8360±40</td><td>9150–9490</td><td>90% charred plant particles, 10% tissues and pollen</td><td>no data</td></tr><tr><td>Poz125905</td><td>132–134</td><td>7330±170</td><td>7790–8460</td><td>80% charred plant particles; 10% minerogenic particles; 10% tissues and pollen</td><td>0.04 not considered</td></tr><tr><td>Poz122367</td><td>136–137</td><td>7510±50</td><td>8190–8400</td><td>80% charred particles, 20% minerogenic particles</td><td>0.35</td></tr></tbody></table>

## 4.5 DISCUSSION

### 4.5.1 Age-depth model

The sequence of the five ¹⁴C-dates clearly indicates a Holocene age of the lake sediments in the Era Kohor subcaldera of the Emi Koussi. Considering the distribution of the ¹⁴C-dates in respect to age versus depth, two possibilities can be proposed: (a) The ¹⁴C-date at 33–36 cm (Poz-122314) exhibits nearly the same age as the lowest sample (Poz-122367). This can be interpreted as indicating very high sedimentation rates, about 1 m during a few centuries around 8200 cal yr BP. The uppermost sample at 0–15 cm dating to about 5400 cal yr BP, would thus point to a marked hiatus between the basal metre and the upper 30 cm. (b) Assuming approximately constant sedimentation rates, the dates at 33–36 cm (Poz-122314) has to be considered as too old. As the lithology seems uniform and there are no distinct features indicating a hiatus in the uppermost 30 cm, we decided to consider possibility (b).

Age-depth models can be approached by linear inter- and extrapolation or by using e.g. Bayesian statistics. The latter method is based on a constrained ordering of the ¹⁴C-dates and simulating numerous different accumulations in between dated depths. Especially for sequences with low dating densities as well as dating scatter and outliers, a Bayesian approach is recommended (Blaauw *et al.* 2018). We therefore chose rbacon to calculate the age depth model. Because no ¹⁴C-dates are available for the basal 10 cm, ages have been extrapolated. The resulting age-depth model is shown in Figure 3: two radiocarbon dates (Poz-122314 and Poz-122367) were omitted during model simulation.
Despite the scattering of the ¹⁴C-dates, our new radiocarbon datings of organic material that is not susceptible to hard water/reservoir effect indicate an Early and Middle Holocene age of the lake remnant. The Bayesian approach, adapted to scattered data, resulted in an age-depth model indicating a deposition of lake sediments between c. 9650 and 5500 cal yr BP.

Based on the published data in Lézine *et al.* (2011b) and complemented by ¹⁴C-dates published in Jäkel and Geyh (1982), an extended dataset of published ¹⁴C-dates for the Tibesti mountains was compiled. Following a modified classification scheme by Lézine *et al.* (2011b), the dates were assigned to the categories lacustrine, fluviatile terraces, playas, palustrine, arid and cultural and summed per millennium (Figure 6). The frequency distribution of dates of lacustrine contexts peaks during the Early Holocene, as do dates from fluviatile terraces. Considering only ¹⁴C-datings other than calcareous crusts, which are possibly susceptible to the hard water effect and volcanic CO₂-gazing, sharpens the peak to the Early Holocene. The newly dated lacustrine sequence from the Emi Koussi caldera, which covers approximately the period 9500–5500 cal yr BP, thus fits into the palaeohydrological scheme of the Tibesti mountain range.

### 4.5.2 Surface pollen sample and present vegetation

The surface sample, a salt crust from the present-day bottom of the sub-caldera, shows a strong dominance of *Ephedra distachya*-type pollen, followed by high *Artemisia* frequencies and some *Anthemis*-type pollen, probably representing *Pentzia* (see Figure 4; *Pentzia* pollen belong to the *Anthemis*-type, cf. Vezey *et al.* 1994). The surface pollen spectrum thus represents the common chamaephyte steppe with the endemic species *Ephedra tilhoana* and *Artemisia tilhoana*, occurring at altitudes between 2400 m asl and the summit (Quézel 1959). The relationship of the endemic *Ephedra tilhoana* is not investigated genetically. Based on morphological traits alone, two *Ephedra* species are assumed to be closely related (or identical) to the Tibestian endemite: *Ephedra major* Host var. *suggarica* Maire (if not flowering/fruiting) and *E. distachya* L. (H. Freitag, pers. comm. 2020), both in accordance with the dominating *Ephedra distachya* pollen type we identified in our samples. The distribution of both taxa indicates the above-stated relation to the (altitudinal) Mediterranean and Asian steppe (see Figure 4). The affinities of the endemic *Artemisia tilhoana* are less clear. The global distribution and core area of *Artemisia* coincide, however, with the distribution of *Ephedra*, pointing similarly to close relations to the oro-Mediterranean and Asian steppes (e.g. Meusel and Jäger 1992).

### 4.5.3 Early to Middle Holocene vegetation at the summit of Emi Koussi

Migration of plant taxa in altitude, changes in the plant composition and substitution of the respective ecosystem are possible vegetation responses to climate fluctuations in mountains (e.g. Messerli and Winiger 1992).

#### 4.5.3.1 Altitudinal plant migration

In order to detect altitudinal migration, we define plant taxa characteristic for the lower montane belt between about 1700 and 2500 m asl which can be traced palynologically. Common genera with distinct pollen types are: *Acacia*, *Rhus*, *Fluggea*, *Capparis*, *Boscia*, *Cordia*, *Commicarpus/Boerhavia*, *Grewia* (tenax) and *Fagonia* (Maire and Monod 1950; Quézel 1959). Some of these types are present in the Early and Middle Holocene spectra: *Acacia*, *Capparis/Cadaba* and *Grewia*. However, in spite of the known under-representation of these pollen types (e.g. Ritchie 1994), the low frequencies point to the presence of these thorn savanna taxa close to highest altitudes, but do not indicate a distinct invasion of tropical plant taxa. The aforementioned and postulated persistence of lower temperatures during the Early and Middle Holocene are a plausible explanation of why there is no marked upward migration of tropical taxa at highest altitudes during the Holocene.
<figure><img src="image_18.png" /><figcaption>**Figure 3.** Stratigraphy, summary pollen diagram and age-depth plot of section W566. (a) Schematic lithography of the sampled section. (b) The grey lines indicate the position and thickness of the ¹⁴C-sample. (c) The black lines indicate the position and thickness of the sampled monoliths. (*) sections constitute a single sample (damaged during transport). (d) Percentage values of a few selected vegetation formations/pollen types are summed up (light grey – altitudinal steppe, dark grey – grasslands, black – ferns) and plotted against the depth, thus indicating the position of the analysed pollen samples. The same graph is plotted against age in Figure 5. The depth scale is the same in all graphs. (e) Age-depth model (simulated with rBacon).</figcaption></figure>
<figure><img src="image_19.png" /></figure>

**Figure 4.** Above: Surface sample. The percentage values of the recorded pollen types are shown. Middle: Photo of the montane steppe at the Emi Koussi. Below: Geographic distribution of the assumed two closest relatives of the endemic *Ephedra tilhoana*, *E. major* Host and *E. distachya* L. Only occurrences documented by plant samples are plotted (GBIF.org).
### 4.5.3.2 *Mediterranean plant taxa migration?*

Lower temperatures in combination with increased moisture should have allowed the spread of Mediterranean tree taxa. Today, as mentioned in the introduction, *Erica arborea* is the only woody taxa with Mediterranean distribution in the Tibesti, occurring in a few small populations in ravines at the Emi Koussi at altitudes between 2500 and 3000 m asl, interpreted as relict. Genetic studies on *Erica arborea* indicate a range of expansion during the Pleistocene from the Eastern Africa/Arabia centre westward, pointing to its oro-African relations while colonizing the Mediterranean region and North Africa. Range fragmentation in Northern Africa resulted in the relicts in the Tibesti mountains (Bruneau de Miré and Quézel 1959; Médail and Quézel 2018) and is connected to the expansion of the Saharan desert. Genetic studies of *Erica arborea* imply a spread of this plant taxa during the African Humid Period (Désamoré *et al.* 2011). Few sporadic pollen records of *Erica* before 6000 cal yr BP and higher frequencies about 6000 cal yr BP may indicate the anticipated expansion near today's relict on the Emi Koussi. With proportions of 6.5% *Erica* pollen in the youngest samples of a Trou au Natron diatomite (Maley 1981), larger *Erica* stands are probable in the Tibesti mountains, corroborated by continuous *Erica* pollen input during the 6th-4th millennia BP in Lake Yoa in the plains E of the Tibesti (Kröpelin *et al.* 2008; Lézine *et al.* 2011a). Except for these *Erica* pollen, no Mediterranean nor Temperate plant taxa (excl. the steppic chamaephytes) are recorded in the sequence of twenty samples from the Era Kohor lake deposit. The few and low frequencies of, e.g. *Pinus* and *Tilia*, are interpreted as long-distance transport. In the palynological investigations of the scattered palaeolake sediments of the Tibesti, neither Mediterranean nor Temperate pollen types are recorded (Maley 1981), in line with palynological re-investigations of Mid-Holocene hyrax midden in the Tassili mountains, evidencing only Mediterranean trees as still present today (Thinon *et al.* 1996). This argument is strengthened by the lack of these elements in the charcoal spectra and only lowest pollen proportions of temperate trees, interpreted as long distance transported, in a joint pollen and charcoal investigation in the Tassili mountains (Amrani 2018). The samples from terraces as well as probably dammed up sediments near Bardai in the Tibesti revealed spectra dominated by temperate and Mediterranean pollen types (compiled in Gabriel 1977). Considering the depositional settings, a re-working of older, Pleistocene sediments bearing Mediterranean and Temperate pollen (see Introduction, Rossignol and Maley 1969) can explain these spectra. Relying on the first sequence from a palaeolake, and underpinned by the above-mentioned investigations (Maley 1981; Thinon *et al.* 1996) and our own ongoing analyses of the Early to Middle Holocene sediments of Lake Yoa (Dinies *et al.* 2019), an expansion of Mediterranean woodlands in the Tibesti can be ruled out, though. Two circumstances or a combination of both can explain the lack of Mediterranean woody taxa. First, the Early and Middle Holocene climatic conditions at high altitudes in the Tibesti mountains were unsuitable (too dry). Second, a migration of Mediterranean (woody) taxa from the source area was not possible during the Holocene, because aridity persisted in the plains north of the Tibesti, and relicts that could expand were not present in the mountains, with the exception of the present *Erica*-relict. The few records of Mediterranean taxa with low frequencies in the Fezzan in the area northwest of the Tibesti mountains and the Central Saharan plains corroborate the latter explanation (e.g. Mercuri 2008; Mercuri *et al.* 1998; Schulz 1991; Trevisan *et al.* 1998).

### 4.5.3.3 *Shift in the plant composition*

The actual pollen spectrum is dominated by the chamaephytes *Ephedra* and *Artemisia*. In contrast Poaceae prevail in the Early and Middle Holocene spectra, together with at times high *Artemisia* proportions and high fern proportions in the lower part of the sequence. This distinct difference between the basal pollen spectra of the palaeolake and the surface sample, though biased by the different type of samples, evidences that at about 9500 cal yrs BP more humid conditions than today were already established at high altitudes in the Tibesti.
<figure><img src="image_20.png" /><figcaption>**Figure 5.** Pollen diagram of section W566. Percentages of pollen types plotted versus age (cal yr BP). Only pollen types present in more than one sample are shown. The first summary graph shows the fluctuations of: light grey – altitudinal steppe, grey – grasslands, black – ferns. The pollen types are grouped according to their ecology.</figcaption></figure>

Ferns still occur today in the Tibesti mountains, however only very rarely and in specific habitats such as shaded fissures and fumerolles at high altitudes, thus in humidity-advantaged localities (Maire and Monod 1950; Quézel 1958). The high fern proportions during the Early and Middle Holocene therefore point to increased humidity, most probably especially to an extended wetter period that fostered their growth, as indicated in the Lake Yoa record in the southeastern foreland (Lézine et al. 2011a). Some scattered palynological investigations of palaeolake sediments in the Tibesti revealed high fern spore proportions which are similarly interpreted as mirroring wetter conditions (Maley 1981). Ferns were also abundantly recorded in an Early
Holocene lacustrine deposit in the present-day desert of Yemen (Lézine et al. 2007). In an analysis of surface samples throughout the African continent, higher fern proportions are assigned to mean annual precipitation amounts >100 mm, peaking about 1200 mm, corroborating the connection to increased humidity (Gajewski et al. 2002). The simultaneously high Poaceae frequencies in our Era Kohor sequence fit into this assumption. Following the interpretation of shifts between *Artemisia* (and Amaranthaceae) versus Poaceae by El Moslimany (1987, 1990), higher grass proportions indicate an increase in humidity during the growing season of grasses. The highest altitudinal pollen spectra in the Early and Middle Holocene thus show a distinct switch in plant composition, indicating increased humidity, probably encompassing a large part of the year. However, despite the marked shift in plant taxa composition, the steppe ecosystem persisted. This is corroborated by the records of additional plant taxa typical for the altitudinal steppes such as *Campanula filicaulis* or *C. bordesiana*, included in the *Campanula* type, or e.g. *Erodium malacoides* included in *Geranium/Erodium* pollen type.

#### 4.5.3.4 Shallow water and riparian vegetation

*Myriophyllum*-type includes the tropical genus *Laurembergia* and *Myriophyllum*. Due to the temperature considerations, an occurrence of *Myriophyllum* is more probable. *Myriophyllum spicatum* occur on the Djebel Marra at elevations between 1160 and 2450 m asl (Wickens 1967), commonly growing in shallow water habitats (Hegi 1975). The continuous record of *Myriophyllum*-type pollen indicates the persistence of a shallow water zone throughout the Early and Middle Holocene. A continuous riparian belt is similarly corroborated by the continuous records of *Typha domingensis* and *Typha latifolia* (Quézel 1958). While *Myriophyllum spicatum* and *Typha* species tolerate brackish water, at least the recent genus *Pediastrum* is mainly restricted to fresh-water habitats, and is very rarely recorded in brackish biotopes (Hegi 1975; Komarek and Jankovska 2001). However, freshwater influxes into a brackish lake may as well explain the occurrence of *Pediastrum*. The riparian and water vegetation thus indicate a shallow and freshwater-to-brackish lake throughout the Holocene, at least at the position of the sampled lake remnants on the slopes of the Era Kohor crater, some 145 m above the caldera floor.

### 4.5.4 Early and Middle Holocene high altitude climate settings derived from montane vegetation

Ferns, grasses and the records of some tropical taxa at highest altitudes suggest humid conditions. In contrast, higher *Artemisia* proportions can be connected to an increase in aridity. Though the genus *Artemisia* is characterized by a wide range of bio-climatic requirements, the opposed progression of grasses and *Artemisia* points to the validity of this assumption for the Tibesti (e.g. Langgut et al. 2011; Lézine et al. 2011a; Subally and Quézel 2002). *Ephedra distachya*-type is another indicator for aridity: low proportions of *Ephedra distachya*-type in the Middle Holocene spectra (cf. also Maley 1981) as compared to its highest frequencies in the surface sample, as well as the general bioclimatic interpretation, evidence its positive correlation with aridity (Gajewski et al. 2002; Qin et al. 2015).

Based on these assumptions, a humidity progression including ferns and Poaceae versus *Artemisia* and *Ephedra distachya*-type may be postulated (Figure 5). Highly fluctuating, but basically more humid conditions characterize the period between 9500 and 8500 cal yrs BP, while three samples about 8000 cal yr BP point to decreased humidity. These more arid conditions may be concomitant with the arid '8.2' identified elsewhere in Africa event (e.g. Gasse 2000). Whether more arid conditions prevailed until about 7000 cal yr BP or whether results are biased by relying on only one sample remains an open question. During the period from about 7000 to 6000 cal yrs BP humidity increased again, however tentatively less distinctly than during the Early Holocene. Interestingly, the humidity index is roughly in line with the frequency distribution of the hydrological indicators: with the peak in lacustrine dated deposits, the humidity index,
<figure><img src="image_21.png" /><figcaption>**Figure 6.** Humidity index and frequency distribution of hydrological indicators by age: (a) Frequency distribution of ¹⁴C-dates from different geomorphological and archaeological formations including all ¹⁴C-datation, (b) excluding the calcareous crusts. Black = lacustrine sediments, grey = fluviatile terraces, grey/dashes = palustrine sediments, grey/lines = playa sediments, white/points = arid settings, white = cultural layers (c) Humidity index: The proportions of Poaceae and ferns versus *Artemisia* and *Ephedra distchya*-type, scaled to 1, are plotted against age. The surface sample mirroring the present climatic conditions is shown as a separate point.</figcaption></figure>

though distinctly fluctuating, reaches high values during the 9th and 8th millennia BP. Both proxies show a depression during the 7th millennium, pointing to reduced humidity, while in the 6th millennium wetter conditions were established again, with a maximum of the humidity index and (augmented) lacustrine and fluviatile sedimentation.

As to precipitation estimates, the major issues are the distinct shift in vegetation composition and the persistence of the steppe ecosystem at high altitudes. To assess rainfall amounts, the bioclimatic requirements of Mediterranean, North African steppes as well as altitudinal, continental dry steppes dominated by dwarf shrubs may be considered. The precipitation marge for the Mediterranean, North African steppes varies between 100 and 400 mm/a (Le Houérou 1995, 2001). To get a notion of the altitudinal factor, altitudinal, continental dry steppes dominated by *Artemisia* in SW Asia (Iran) may additionally be considered an equivalent. In an altitudinal vegetation-pollen-rain transect in SW Iran, rainfall amounts of about 100–300 mm/a are assigned to *Artemisia*-dominated steppes at altitudes about 800-1500 m asl mirrored by high *Artemisia* pollen proportions. The subsequent, treeless montane and alpine grass-dominated belt at >1500 m asl, characterized in the pollen spectra by high Poaceae frequencies, profits from orographic rainfall increase of about 300–500 mm/a (Dehghani *et al.* 2017). Because of the recurrent high *Artemisia* proportions in the W566 sequence, underpinned by high *Artemisia* frequencies in a sample from another Early Holocene lake remnant of Emi Koussi (Maley 1981), a range near the threshold between *Artemisia* – Poaceae dominated zones may be assumed at about 300–400 mm/a,
and up to 500 mm/a for the grass-dominated sections. By applying the actual adiabatic lapse rate (roughly 50 mm per 1000 m), rainfall similarly would amount to 370–540 mm/a. Precipitation estimates for the Middle Holocene in the Ounianga Basin southwest of the Tibesti massif based on transfer functions resulted in 250–420 mm/a (Kröpelin *et al.* 2008; Lézine *et al.* 2011a). At present <5 mm/a are indicated for the Ounianga Basin and 80–150 mm/a are estimated for the high altitudes of the Emi Koussi. Indications concerning temperature fluctuations are less distinct. The lack of a mass expansion of tropical trees points to (persisting) low temperatures. Diatom spectra of the Emi Koussi similarly speak in favour of persisting low or even lower temperatures at the beginning of lake formation (Messerli 1972). Both assumptions are in line with continental scale pollen-based climate reconstructions at 6000 years BP for the region Northern Chad and Southern Libya, indicating an increase of precipitation >200 mm/a with an inconsistent pattern for temperature, however also in parts indicating a temperature decrease, resulting from an increased monsoon (Bartlein *et al.* 2011).

## 4.6 SUMMARY AND CONCLUSIONS

The age-depth model of a lake remnant based on ¹⁴C-dates of charred plant material and the investigation of a sequence of 20 pollen samples from this palaeolake in the Emi Koussi crater, SE Tibesti mountains, allow inferences on some pending issues:

There is no palynological evidence of an Early and Middle Holocene expansion of Mediterranean (and Temperate) plant taxa in the Tibesti mountains (except for the relict *Erica*). For the first time, a palynological sequence has been analysed, improving the previously erratic data basis of single pollen samples. None of the newly investigated pollen samples shows higher frequencies of Mediterranean or Temperate taxa. This is in line with the single-sample palynological investigation of lake remnants in the Trou au Natron and the SE Tibesti (Emi Koussi, MouskORBÉ, Tarso Yega, Maley 1981). Neither a re-migration of Mediterranean tree taxa from the north, nor an expansion from possible refuge habitats was thus possible during the Holocene. A rather poorly developed palaeohydrological network reconstructed for the surroundings of the Tibesti (HydroSHEDS; https://www.hydrosheds.org/) seems to corroborate its more isolated situation when compared to the Hoggar mountains in the NW, where there are more Mediterranean tree relicts (*Cupressus dupreziana*, *Olea europaea* subsp. *laperrinei* e.g. Quézel 1965). An exception is the spread of *Erica arborea* at the end of the African Humid Period in the Tibesti. However, relict stands of *Erica* continue to exist today at the Emi Koussi. Similarly, *Erica arborea* may have outlasted the last Glacial and expanded under favourable conditions about 6000 years ago.

Lake formation at the highest altitudes of the Tibesti and the surrounding plains is synchronous. The radiocarbon-dated charred plant particles from the diatomite W566 of the Era Kohor caldera clearly indicate its Holocene age. The lake formation at highest altitudes thus fits into the main phase of lake and terraces formation in the Tibesti mountains, as shown by the frequency distribution of ¹⁴C-dates of these geomorphological formations – and is synchronous to the well-defined palaeolake phase in the Saharan plains (e.g. Cremaschi and Zerboni 2009; Hoelzmann *et al.* 1998; Holmes and Hoelzmann 2017; Kuper and Kröpelin 2006; Lézine *et al.* 2011b; Lécuyer *et al.* 2016; van Neer *et al.* 2020). This does not exclude an increase in humidity pre-dating the formation of lakes: the high Poaceae frequencies in the basal pollen samples of the Emi Koussi sequence indicate wetter conditions already at the beginning of lake formation.

Distinct changes in plant composition with the persistence of the montane steppe ecosystem indicate increased humidity and probably continued low temperatures. Palynological investigations on the W566 lake sediments in the Era Kohor sub-caldera document the persistence of a steppe at high altitudes. Changed climatic conditions, however, are indicated by high Poaceae and fern frequencies and strongly fluctuating *Artemisia* proportions during the African Humid period versus strongly dominating *Ephedra distachya*-type proportions, together with *Artemisia*,
reflecting the present vegetation. The resultant calculated humidity index indicates wetter conditions during the Early Holocene, more arid conditions about 8200–8000 cal yr BP presumably lasting until about 7000 cal yr BP, and an increase in humidity during the 6th millennium.

In analogy to Mediterranean and Asian chamaephyte steppes, a three- to fivefold increase in precipitation (c. 400–550 mm/a) may be estimated. The lack of a mass expansion of tropical taxa at high altitudes points to persisting low temperatures during the African Humid period. Holocene climate fluctuations thus impacted the surrounding plains more strongly, triggering large-scale ecosystem changes. High altitudinal ecosystems in the Tibesti were less affected, probably in consequence of the persisting specific climatic conditions (low temperatures) that still prevail today due to the singular geographic position of the Tibesti between the Mediterranean and the tropical climate regimes.

With its additional habitats such as riparian vegetation and additional grass-dominated plant formations at highest altitudes, the mountain ranges of the Tibesti may have attracted humans and wild animal populations. Due to the more stable conditions than in the plains, the Tibesti has acted (and acts) as a refuge, e.g. for *Ephedra* during the African Humid period or today for *Erica* relict stands – which of course holds true for humans and animals as well.

## 4.7 ACKNOWLEDGEMENTS

This study is supported by a grant from the DFG priority program SPP 1234 'Entangled Africa'. DEM data were provided by the DLR (Deutsches Zentrum für Luft- und Raumfahrt/German Aerospace Center). Fieldwork was supported by DFG project 57444011-SFB806. We are grateful to Dr. Baba Mallaye, Director of the Centre National de la Recherche pour le Développement (CNRD) in N'Djaména, for his comprehensive support of the missions. We also thank our team members Jan Kuper and Mahadi Chaha for their help with the sampling. We thank an anonymous reviewer and Jean Maley for their most fruitful reviews and suggestions which most significantly improved the manuscript.

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<figure><img src="image_22.png" /></figure>

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CHAPTER 5

# Timing and nature of the end of the African Humid Period in the Sahel: Insight from pollen data

Kévin Lemonnier & Anne-Marie Lézine

*Laboratoire d'Océanographie et du Climat, Expérimentation et Approche Numérique/IPSL, Sorbonne Université, CNRS-IRD-MNHN, Paris, France*

**ABSTRACT:** Pollen, spores, and algae from a 4m-long sediment core at the Mboro-Baobab site (15°8′58.49″N, 16°54′34.37″W), in the Niayes region of Senegal were used to provide a record of the end of the African Humid Period (AHP) in the western Sahel. We show that the drying of the Mboro-Baobab landscape was gradual, starting from 3750 cal yr BP then culminating at 1300 cal yr BP. In contrast, the response of the lake system and the gallery forest developed in two main phases: the sharp decline of tropical humid forest elements at 3200 cal yr BP followed by the almost complete collapse of the gallery forests at 2500 cal yr BP. Our results are consistent with those from the central Sahel, which show a gradual transition from the AHP to the modern landscape.

## 5.1 INTRODUCTION

At the end of the African Humid Period (AHP), tropical North Africa experienced a major environmental crisis. The southward displacement of the desert margin (Kuper and Kröpelin 2006) with the related loss in biodiversity (Hély *et al.* 2014; Watrin *et al.* 2009) along with the decline of wetlands (Lézine *et al.* 2011) had dramatic consequences for human populations through a decline in population density, cultural adaptations with the development of pastoralism and migrations toward the main rivers (Nile, Senegal, Niger) (Manning and Timpson 2014 and references therein) and the Equatorial forest block (Lézine *et al.* 2013). How long was this transition from a “green Sahara” to the hyper-arid desert of today? This question remains largely unanswered, as the number of palaeorecords with adequate temporal resolution and age control is low and often contradictory. Based on marine records, deMenocal *et al.* (2000) showed that an abrupt increase in dust transport to the ocean between 5579 and 5299 cal yr BP marked the end of the AHP in the Saharan desert. Studies in the central Sahara suggested that the modern desert was definitely established at 2700 cal yr BP after a period of gradual drying likely originating from the mid-Holocene and intensifying at 4300 cal yr BP (Kröpelin *et al.* 2008; Lézine *et al.* 2011; Lécuyer *et al.* 2016).

In the Sahel, interdunal depressions of Senegal and Nigeria provided detailed records of environmental change during the AHP (Lézine 1988; 1989; Salzmann and Waller 1998; Waller *et al.* 2007). The presence of a water table near the surface favored the development of forest galleries along water bodies. However, pollen studies suggest a contrasted situation: in Senegal, an abrupt change c. 2500 cal yr BP, interpreted as the crossing of a biological threshold, brought about the destruction of the forests and the decline of tropical humid elements (Lézine 1989).
In Nigeria, the modern vegetation was established earlier, c. 3300 cal yr BP (Salzmann and Waller 1998). However, new data from Jikaryia Lake (Waller et al. 2007) suggest that “rather than a single abrupt event, Late Holocene aridification appears to have occurred progressively” from 4700 cal yr BP onward. Here we present a new and high-resolution pollen record from Mboro-Baobab in the “Niayes” coastal region of Senegal (15°8′58.49″N, 16°54′34.37″W). We focus on the period between 4300 cal yr BP (the base of the Mboro-Baobab pollen sequence) and the last millennium, which has been the subject of a separate publication (Lézine et al. 2019). Our goal is to determine whether the transition from AHP to the present was abrupt or gradual in this area, to discuss the turnover of species and the response times of forest trees to changes in hydrological conditions.

## 5.2 GENERAL SETTING

Niayes are interdunal depressions with accumulations of organic sediments, formed between linear fixed and partially fixed coastal dune ridges, located along the Atlantic coast between 15° N and 16° N, at roughly 17° W. The mean annual rainfall (369 mm) is characteristic of the Sahel, but in response to local soil moisture conditions, the depressions support an array of plant communities that include an azonal extension north of Guinean humid forests and Sudanian dry forests and wooded grasslands (Trochain 1940) (Figure 1A).

The Mboro-Baobab depression is located 2.3 km from the seashore west of the Mboro paleoriver (Figure 1B), at the edge of the central zone of the Niayes where the sub-surface aquifer is the most developed (Putallaz, 1964). The Mboro-Baobab depression is 570 m long and 310 m wide. To the south, it is covered with vegetation and partially exploited for agricultural purposes.

<figure><img src="image_23.png" /><figcaption>**Figure 1.** (A) vegetation map of Senegal from Trochain (1940) showing the azonal position of the Niayes along the Atlantic Ocean, north of the Dakar peninsula. Trochain described the vegetation of the Niayes as belonging to a "sub-Guinean domain" owing to its strong relation with the Guinean (rain) forests today found in the Casamance region, south of Senegal. (B) Location map of the Mboro-Baobab interdunal depression west of the Mboro paleoriver channel. In gray, inundated sectors (ORSTOM 1962). (C) Satellite image showing the Mboro- Baobab depression surrounded by dunes fields covered with Sahelian vegetation. The localization of the core in the northern part of the depression is shown.</figcaption></figure>
Its northern part is an open water basin of 270 m by 90 m wide and 0.4 m maximum depth (Figure 1C). Mboro-Baobab is currently filled by brackish waters and occasionally desiccated.

## 5.3 MATERIAL AND METHODS

A 4 m long core was collected near the northeastern shore of the open water basin using a manual Russian corer (Jowsey 1966) in 2016 (Lézine *et al.* 2019). It was divided into 8 sections of 50 cm each. The sediment consists of homogeneous organic clay. Samples (1 cm³ each) were taken at 5 cm intervals for pollen and non-pollen palynomorphs (NPP = freshwater algae (*Pediastrum*, *Botryococcus*, *Coelastrum*, *Scenedesmus*, *Tetraedron* and undifferentiated fungi) analyses. They were processed using the standard HF method described by Faegri and Iversen (1977). Pollen identification was based on the reference slide and photo collections of the LOCEAN laboratory and the Musée National d'Histoire Naturelle in Paris as well as on pollen atlases of tropical African flora from e.g. Maley (1970), APLF (1974), Ybert (1979) and Bonnefille and Riollet (1980). Pollen nomenclature, which follows the standard defined by the African Pollen Database (Vincens *et al.* 2007), was based on Lebrun and Stork (1991-2015). The pollen spectra was composed of 105 taxa among which 57 trees, shrubs, lianas and palms, 21 herbs, 16 undifferentiated (trees, shrubs or herbs), 7 aquatics and 4 ferns (Table 1). Pollen taxa have been grouped according to the phytogeographical affinity of the parent plants following Trochain (1940) and White (1983) (Table 1).

<table><caption>**Table 1.** Mboro-Baobab pollen taxa. A: trees; AL: tree/lianas; L: lianas; I: undifferentiated; N: herbs; Nq: aquatics. Nomenclature from the African Pollen Database. According to Vincens *et al.* (2007) a "type" is added to the name of the taxon (1) to the genus when several plant genera display similar pollen morphology. The species name can be added in case of monospecificity or when the species is dominant or characteristic in the study area (2) to the species when, the genus being clearly identified, several species can be concerned. SH: Saharan. SL: Sahelian; SU: Sudanian; GU: Guinean.</caption><thead><tr><th>Family</th><th>Taxon</th><th>Life form</th><th>SH</th><th>SL</th><th>SU</th><th>GU</th></tr></thead><tbody><tr><td rowspan="3">ACANTHACEAE</td><td><i>Hygrophila</i></td><td>N</td><td></td><td></td><td>x</td><td></td></tr><tr><td><i>Justicia</i>-type</td><td>I</td><td></td><td>x</td><td>x</td><td></td></tr><tr><td><i>Justicia</i>-type <i>flava</i></td><td>N</td><td></td><td>x</td><td>x</td><td></td></tr><tr><td rowspan="9">AMARANTHACEAE</td><td><i>Achyranthes</i>-type <i>aspera</i></td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td><i>Aerva</i>-type <i>lanata</i></td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td><i>Alternanthera</i></td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td>Amaranthaceae undiff.</td><td>I</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td><i>Celosia</i>-type <i>trigyna</i></td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td><i>Chenopodium</i>-type</td><td>N</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td><i>Gomphrena</i></td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td><i>Suaeda</i></td><td>I</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td rowspan="2">ANACARDIACEAE</td><td>Anacardiaceae undiff.</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Lannea</i>-type</td><td>A</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td>APIACEAE</td><td>Apiaceae undiff.</td><td>I</td><td></td><td>x</td><td>x</td><td></td></tr></tbody></table>

(continued)
<table><caption>**Table 1. Continued.**</caption><thead><tr><th>Family</th><th>Taxon</th><th>Life form</th><th>SH</th><th>SL</th><th>SU</th><th>GU</th></tr></thead><tbody><tr><td rowspan="2">APOCYNACEAE</td><td>Apocynaceae undiff.</td><td>I</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td>Tabernaemontana</td><td>AL</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td rowspan="2">ARECACEAE</td><td>Elaeis guineensis</td><td>PA</td><td></td><td></td><td></td><td>x</td></tr><tr><td>Phoenix reclinata-type</td><td>PA</td><td>x</td><td>x</td><td>x</td><td>x</td></tr><tr><td>ASCLEPIADACEAE</td><td>Gymnema</td><td>AL</td><td>x</td><td></td><td></td><td></td></tr><tr><td rowspan="3">ASTERACEAE</td><td>Asteraceae undiff.</td><td>I</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td>Centaurea-type perrottetii</td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td>Cichorieae undiff.</td><td>I</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td>BOMBACACEAE</td><td>Adansonia digitata</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>BURSERACEAE</td><td>Commiphora africana-type</td><td>A</td><td></td><td>x</td><td>x</td><td></td></tr><tr><td>CAESALPINIACEAE</td><td>Detarium senegalense</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td rowspan="2">CAPPARACEAE</td><td>Capparis fascicularis-type</td><td>AL</td><td></td><td>x</td><td>x</td><td></td></tr><tr><td>Cleome-type gynandra</td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td rowspan="5">CARYOPHYLLACEAE</td><td>Caryophyllaceae undiff.</td><td>I</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td>Cerastium-type</td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td>Polycarpaea-type</td><td>N</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td>Polycarpon-type</td><td>N</td><td>x</td><td>x</td><td>x</td><td>x</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>CASUARINACEAE</td><td>Casuarina equisetifolia-type</td><td>A</td><td></td><td></td><td></td><td></td></tr><tr><td rowspan="2">CELASTRACEAE</td><td>Celastraceae undiff.</td><td>AL</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td>Salacia</td><td>AL</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>CHRYSOBALANACEAE</td><td>Chrysobalanus/Parinari</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>COMBRETACEAE</td><td>Combretaceae undiff.</td><td>A</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td rowspan="2">COMMELINACEAE</td><td>Commelina-type benghalensis</td><td>N</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td>Commelina-type forskalaei</td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td rowspan="2">CONVOLVULACEAE</td><td>Convolvulus-type</td><td>N</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td>Ipomoea-type</td><td>I</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td>CYPERACEAE</td><td>Cyperaceae undiff.</td><td>Nq</td><td></td><td></td><td></td><td></td></tr><tr><td>DILLENIACEAE</td><td>Tetracera</td><td>AL</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td rowspan="2">EBENACEAE</td><td>Diospyros</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>Ebenaceae undiff.</td><td>A</td><td></td><td></td><td></td><td></td></tr><tr><td>EPHEDRACEAE</td><td>Ephedra</td><td>AL</td><td>x</td><td></td><td></td><td></td></tr></tbody></table>

(continued)
<table><caption>**Table 1. Continued.**</caption><thead><tr><th>Family</th><th>Taxon</th><th>Life form</th><th>SH</th><th>SL</th><th>SU</th><th>GU</th></tr></thead><tbody><tr><td rowspan="10">EUPHORBIACEAE</td><td><i>Acalypha</i></td><td>I</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Alchornea</i></td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Anthostema</i>-type</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Antidesma</i>-type</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Bridelia</i>-type</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Erythrococca</i>-type</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Hymenocardia</i></td><td>A</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td><i>Macaranga</i>-type</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Mallotus</i>-type</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Uapaca</i></td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>FABACEAE</td><td><i>Aeschynomene</i></td><td>I</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>HALORRHAGACEAE</td><td><i>Laurembergia tetrandra</i></td><td>Nq</td><td></td><td></td><td></td><td></td></tr><tr><td>LAMIACEAE</td><td><i>Basilicum</i>-type <i>polystachyon</i></td><td>N</td><td></td><td></td><td>x</td><td></td></tr><tr><td>LORANTHACEAE</td><td><i>Tapinanthus</i>-type</td><td>L</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td>MALVACEAE</td><td><i>Hibiscus</i></td><td>I</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td>MELIACEAE</td><td><i>Khaya</i>-type <i>senegalensis</i></td><td>A</td><td></td><td></td><td></td><td>x</td></tr><tr><td rowspan="3">MENISPERMACEAE</td><td><i>Cissampelos</i>-type</td><td>AL</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td><i>Cocculus</i></td><td>L</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td><i>Tinospora bakis</i></td><td>L</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td rowspan="2">MIMOSACEAE</td><td><i>Acacia</i></td><td>AL</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td><i>Prosopis</i>-type <i>africana</i></td><td>A</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td rowspan="3">MORACEAE</td><td><i>Ficus</i></td><td>A</td><td></td><td>x</td><td>x</td><td></td></tr><tr><td><i>Musanga</i>-type</td><td>A</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td><i>Myrianthus</i>-type</td><td>A</td><td></td><td></td><td></td><td>x</td></tr><tr><td>MYRTACEAE</td><td><i>Syzygium</i>-type <i>guineense</i></td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>NYMPHAEACEAE</td><td><i>Nymphaea</i></td><td>Nq</td><td></td><td></td><td></td><td></td></tr><tr><td>OCHNACEAE</td><td><i>Lophira</i></td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>ONAGRACEAE</td><td><i>Ludwigia</i>-type <i>ascendens</i></td><td>Nq</td><td></td><td></td><td></td><td></td></tr><tr><td>POACEAE</td><td>Poaceae undiff.</td><td>N</td><td>x</td><td>x</td><td>x</td><td>x</td></tr><tr><td>POLYGALACEAE</td><td><i>Polygala</i>-type</td><td>I</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td>POLYGONACEAE</td><td><i>Polygonum senegalense</i></td><td>Nq</td><td></td><td></td><td></td><td></td></tr><tr><td>POTAMOGETONACEAE</td><td><i>Potamogeton</i></td><td>Nq</td><td></td><td></td><td></td><td></td></tr></tbody></table>

(continued)
<table><caption>**Table 1. Continued.**</caption><thead><tr><th>Family</th><th>Taxon</th><th>Life form</th><th>SH</th><th>SL</th><th>SU</th><th>GU</th></tr></thead><tbody><tr><td>RANUNCULACEAE</td><td>Clematis-type</td><td>AL</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td rowspan="8">RUBIACEAE</td><td>Leptactina</td><td>A</td><td></td><td></td><td></td><td>x</td></tr><tr><td>Hymenodictyon-type</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>Ixora-type</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>Mitracarpus villosus</td><td>N</td><td></td><td>x</td><td>x</td><td></td></tr><tr><td>Mitragyna-type inermis</td><td>A</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td>Morelia senegalensis</td><td>A</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td>Pavetta</td><td>AL</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>Rubiaceae undiff.</td><td>I</td><td>x</td><td>x</td><td>x</td><td>x</td></tr><tr><td>Spermacoce-type radiata</td><td>N</td><td></td><td>x</td><td>x</td><td></td></tr><tr><td>RUTACEAE</td><td>Zanthoxylum-type zanthoxyloides</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>SALVADORACEAE</td><td>Salvadora persica-type</td><td>A</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td rowspan="3">SAPINDACEAE</td><td>Allophylus</td><td>AL</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>Paullinia pinnata</td><td>L</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>Sapindaceae undiff.</td><td>AL</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td rowspan="2">SAPOTACEAE</td><td>Sapotaceae undiff.</td><td>AL</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>Vitellaria-type paradoxa</td><td>A</td><td></td><td></td><td></td><td>x</td></tr><tr><td>SOLANACEAE</td><td>Solanum-type</td><td>I</td><td>x</td><td>x</td><td>x</td><td></td></tr><tr><td>STERCULIACEAE</td><td>Dombeya-type</td><td>A</td><td></td><td></td><td>x</td><td>x</td></tr><tr><td>TAMARICACEAE</td><td>Tamarix</td><td>A</td><td>x</td><td>x</td><td></td><td></td></tr><tr><td>TILIACEAE</td><td>Triumfetta-type</td><td>I</td><td></td><td>x</td><td>x</td><td></td></tr><tr><td>TYPHACEAE</td><td>Typha</td><td>Nq</td><td></td><td></td><td></td><td></td></tr><tr><td>ULMACEAE</td><td>Celtis</td><td>A</td><td></td><td>x</td><td>x</td><td>x</td></tr><tr><td>ZYGOPHYLLACEAE</td><td>Tribulus</td><td>N</td><td>x</td><td>x</td><td></td><td></td></tr></tbody></table>

Data are presented as percentages and influx values (number of grains/cm²/year) and diagrams are drawn using Tilia and CONISS (Grimm 1991). Pollen percentages were calculated against a sum excluding aquatics and ferns, the percentages of which were calculated separately against a sum including all the pollen grains and fern spores counted. Algae and fungi percentages were calculated against the sum of NPP. Correspondence statistical analyses (CA) were performed on the raw pollen counts using the Package 'Rcmdr/FactoMinR' (Husson et al. 2020).

An age model was derived from three Accelerator Mass Spectrometry (AMS) radiocarbon dates and an additional control point given by the first occurrence of *Casuarina equisetifolia* pollen grains, the parent trees of which were planted in 1948 along the coast (Ndiaye et al. 1993), using the Bacon age-depth modeling (Blaauw and Christen 2011) from calibrated ¹⁴C ages (Reimer et al. 2013) (Table 2).
<table><caption>**Table 2.** Mboro-Baobab ages. Radiocarbon dating (99.5 cm, 299.5 cm, and 399.5 cm) was conducted at UMS-ARTEMIS AMS Facilities (France). At 30.5 cm downcore, the first appearance of *Casuarina equisetifolia* pollen grains provide a date of 1948 CE. The age of the surface is that of coring (from Lézine *et al.* 2019).</caption><thead><tr><th>Lab.<br>number</th><th>Mean<br>depth (cm)</th><th>Nature</th><th>Radiocarbon<br>Age BP</th><th>Error</th><th>δ<sup>13</sup>C</th><th>Age cal<br>yr BP</th></tr></thead><tbody><tr><td></td><td>0</td><td>Date of coring</td><td></td><td></td><td></td><td>-66</td></tr><tr><td></td><td>30.5</td><td>Casuarina pollen</td><td></td><td></td><td></td><td>-2</td></tr><tr><td>49827</td><td>99.5</td><td>Bulk sediment</td><td>580</td><td>30</td><td>-22.40‰</td><td>604</td></tr><tr><td>49828</td><td>299.5</td><td>Bulk sediment</td><td>3265</td><td>30</td><td>-28.60‰</td><td>3496</td></tr><tr><td>49829</td><td>399.5</td><td>Bulk sediment</td><td>3865</td><td>30</td><td>-29.10‰</td><td>4298</td></tr></tbody></table>

## 5.4 POLLEN DIAGRAM

Based on the variations in percentages of the main pollen taxa and NPP types, four zones corresponding to the main phases of landscape evolution over the last 4300 years can be distinguished. Zones 3 and 4 were presented in detail in Lézine *et al.* (2019, Figure 2).

### 5.4.1 Zone 1A: 4300 – 3700 cal yr BP

Guinean tree taxa such as *Mallotus* (3%), *Zanthoxylum* (2.4%), *Uapaca* (2.5%), *Alchornea* (15%) and *Macaranga* (11%) characterized this zone. Lakeshore populations are reduced with *Typha* percentages less than 1%.

Among the NPPs, *Pediastrum* and *Coelastrum* are largely dominant with percentages that can reach values above 80% for *Pediastrum* and 30% for *Coelastrum*.

### 5.4.2 Zone 1B: 3700 – 3050 cal yr BP

There is little change from the previous zone. However, the forest taxa listed above decreased significantly (e.g. *Uapaca* (0.3%)). Other tree taxa such as *Lannea* (1.2%) and *Mitragyna* (1.2%) increased, along with taxa from lakeshore populations, *Syzygium* (7.2%) and *Elaeis* (1.2%). Upland herbaceous taxa, such as *Amaranthaceae* and *Aerva*, which were occasionally present in zone 1A, also increased. However, their percentages remained low (less than 1.5%).

Among the NPPs, this zone is characterized by the rapid development of *Tetraedron*, which reached up to 80% reflecting the onset of the lake level lowering.

### 5.4.3 Zone 2A: 3050 – 1600 cal yr BP

This zone is characterized by the sharp increase in *Typha* percentages (15%) and the more gradual increase of Cyperaceae (22.8%) showing the development of reed swamp populations around the lake. Among the trees, *Mallotus* or *Uapaca* gradually decrease to less than 0.5%, whereas *Alchornea* increased (16.5%). Dry herbaceous taxa, such as *Mitracarpus* and *Spermacoce*, already present previously, increased with percentages up to 4%.

NPP are characterized by the progressive increase in the percentages of *Botrycoccus*, (maximum = 17%).

### 5.4.4 Zone 2B: 1600 – 700 cal yr BP

Cyperaceae (23%) then *Elaeis* (2.6%) increased in this zone. Some tree taxa of Guinean affinity (*Mallotus*, *Anthostema*, *Zanthoxylum*, *Celtis*) or wetlands decreased or even disappeared
<figure><img src="image_24.png" /></figure>

**Figure 2.** Figure showing from left to right, a simplified diagram of pollen percentages for Mboro-Baobab (Senegal). Black shading shows selected taxa. Light-gray shading shows the same results, multiplied by 10 for highlighting. On the right, the main NPP (Algae and Fungi) are shown.

almost completely, while others were stable (*Alchornea* 19%) or even increased (*Detarium* 2.1%, *Mitragyna* 1.6%). *Typha* percentages decreased significantly (5%) while another aquatic plant, *Potamogeton* (1.9%), appeared.

Among the NPPs, *Tetraedron* and *Botryococcus* continued to increase until reaching 85% and 47%, respectively.