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An unexpectedly large count of trees in the West African Sahara and Sahel

Author

Listed:
  • Martin Brandt

    (University of Copenhagen
    Science Systems and Applications Inc., NASA Goddard Space Flight Center)

  • Compton J. Tucker

    (NASA Goddard Space Flight Center)

  • Ankit Kariryaa

    (Science Systems and Applications Inc., NASA Goddard Space Flight Center
    HCI Group, University of Bremen)

  • Kjeld Rasmussen

    (University of Copenhagen)

  • Christin Abel

    (University of Copenhagen)

  • Jennifer Small

    (Science Systems and Applications Inc., NASA Goddard Space Flight Center
    NASA Goddard Space Flight Center)

  • Jerome Chave

    (Université Paul Sabatier)

  • Laura Vang Rasmussen

    (University of Copenhagen)

  • Pierre Hiernaux

    (Science Systems and Applications Inc., NASA Goddard Space Flight Center
    Pastoralisme Conseil)

  • Abdoul Aziz Diouf

    (Centre de Suivi Ecologique)

  • Laurent Kergoat

    (Geosciences Environnement Toulouse (GET), Observatoire Midi-Pyrénées, UMR 5563 (CNRS/UPS/IRD/CNES))

  • Ole Mertz

    (University of Copenhagen)

  • Christian Igel

    (University of Copenhagen)

  • Fabian Gieseke

    (University of Copenhagen
    University of Műnster)

  • Johannes Schöning

    (HCI Group, University of Bremen)

  • Sizhuo Li

    (University of Copenhagen)

  • Katherine Melocik

    (Science Systems and Applications Inc., NASA Goddard Space Flight Center
    NASA Goddard Space Flight Center)

  • Jesse Meyer

    (Science Systems and Applications Inc., NASA Goddard Space Flight Center
    NASA Goddard Space Flight Center)

  • Scott Sinno

    (Science Systems and Applications Inc., NASA Goddard Space Flight Center
    NASA Goddard Space Flight Center)

  • Eric Romero

    (Science Systems and Applications Inc., NASA Goddard Space Flight Center
    NASA Goddard Space Flight Center)

  • Erin Glennie

    (Science Systems and Applications Inc., NASA Goddard Space Flight Center
    NASA Goddard Space Flight Center)

  • Amandine Montagu

    (Ecole Normale Supérieure)

  • Morgane Dendoncker

    (Université Catholique de Louvain)

  • Rasmus Fensholt

    (University of Copenhagen)

Abstract

A large proportion of dryland trees and shrubs (hereafter referred to collectively as trees) grow in isolation, without canopy closure. These non-forest trees have a crucial role in biodiversity, and provide ecosystem services such as carbon storage, food resources and shelter for humans and animals1,2. However, most public interest relating to trees is devoted to forests, and trees outside of forests are not well-documented3. Here we map the crown size of each tree more than 3 m2 in size over a land area that spans 1.3 million km2 in the West African Sahara, Sahel and sub-humid zone, using submetre-resolution satellite imagery and deep learning4. We detected over 1.8 billion individual trees (13.4 trees per hectare), with a median crown size of 12 m2, along a rainfall gradient from 0 to 1,000 mm per year. The canopy cover increases from 0.1% (0.7 trees per hectare) in hyper-arid areas, through 1.6% (9.9 trees per hectare) in arid and 5.6% (30.1 trees per hectare) in semi-arid zones, to 13.3% (47 trees per hectare) in sub-humid areas. Although the overall canopy cover is low, the relatively high density of isolated trees challenges prevailing narratives about dryland desertification5–7, and even the desert shows a surprisingly high tree density. Our assessment suggests a way to monitor trees outside of forests globally, and to explore their role in mitigating degradation, climate change and poverty.

Suggested Citation

  • Martin Brandt & Compton J. Tucker & Ankit Kariryaa & Kjeld Rasmussen & Christin Abel & Jennifer Small & Jerome Chave & Laura Vang Rasmussen & Pierre Hiernaux & Abdoul Aziz Diouf & Laurent Kergoat & Ol, 2020. "An unexpectedly large count of trees in the West African Sahara and Sahel," Nature, Nature, vol. 587(7832), pages 78-82, November.
  • Handle: RePEc:nat:nature:v:587:y:2020:i:7832:d:10.1038_s41586-020-2824-5
    DOI: 10.1038/s41586-020-2824-5
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    Citations

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    Cited by:

    1. Florian Reiner & Martin Brandt & Xiaoye Tong & David Skole & Ankit Kariryaa & Philippe Ciais & Andrew Davies & Pierre Hiernaux & Jérôme Chave & Maurice Mugabowindekwe & Christian Igel & Stefan Oehmcke, 2023. "More than one quarter of Africa’s tree cover is found outside areas previously classified as forest," Nature Communications, Nature, vol. 14(1), pages 1-10, December.
    2. Nicholas A. O’Mara & Charlotte Skonieczny & David McGee & Gisela Winckler & Aloys J.-M. Bory & Louisa I. Bradtmiller & Bruno Malaizé & Pratigya J. Polissar, 2022. "Pleistocene drivers of Northwest African hydroclimate and vegetation," Nature Communications, Nature, vol. 13(1), pages 1-11, December.
    3. Martin Brandt & Dimitri Gominski & Florian Reiner & Ankit Kariryaa & Venkanna Babu Guthula & Philippe Ciais & Xiaoye Tong & Wenmin Zhang & Dhanapal Govindarajulu & Daniel Ortiz-Gonzalo & Rasmus Fensho, 2024. "Severe decline in large farmland trees in India over the past decade," Nature Sustainability, Nature, vol. 7(7), pages 860-868, July.
    4. Luc Descroix & Anne Luxereau & Laurent A. Lambert & Olivier Ruë & Arona Diedhiou & Aïda Diongue-Niang & Amadou Hamath Dia & Fabrice Gangneron & Sylvie Paméla Manga & Ange B. Diedhiou & Julien Andrieu , 2024. "An Interdisciplinary Approach to Understand the Resilience of Agrosystems in the Sahel and West Africa," Sustainability, MDPI, vol. 16(13), pages 1-19, June.
    5. Nina Tiel & Fabian Fopp & Philipp Brun & Johan Hoogen & Dirk Nikolaus Karger & Cecilia M. Casadei & Lisha Lyu & Devis Tuia & Niklaus E. Zimmermann & Thomas W. Crowther & Loïc Pellissier, 2024. "Regional uniqueness of tree species composition and response to forest loss and climate change," Nature Communications, Nature, vol. 15(1), pages 1-12, December.
    6. Xuehui Pi & Qiuqi Luo & Lian Feng & Yang Xu & Jing Tang & Xiuyu Liang & Enze Ma & Ran Cheng & Rasmus Fensholt & Martin Brandt & Xiaobin Cai & Luke Gibson & Junguo Liu & Chunmiao Zheng & Weifeng Li & B, 2022. "Mapping global lake dynamics reveals the emerging roles of small lakes," Nature Communications, Nature, vol. 13(1), pages 1-12, December.
    7. Yan Cheng & Stefan Oehmcke & Martin Brandt & Lisa Rosenthal & Adrian Das & Anton Vrieling & Sassan Saatchi & Fabien Wagner & Maurice Mugabowindekwe & Wim Verbruggen & Claus Beier & Stéphanie Horion, 2024. "Scattered tree death contributes to substantial forest loss in California," Nature Communications, Nature, vol. 15(1), pages 1-13, December.
    8. Grabher, Harald F. & Erb, Karlheinz & Singh, Simron & Haberl, Helmut, 2024. "Household energy systems based on biomass: Tracing material flows from source to service in rural Ethiopia," Ecological Economics, Elsevier, vol. 217(C).
    9. Lucas R. Vargas Zeppetello & Susan C. Cook-Patton & Luke A. Parsons & Nicholas H. Wolff & Timm Kroeger & David S. Battisti & Joseph Bettles & June T. Spector & Arjun Balakumar & Yuta J. Masuda, 2022. "Consistent cooling benefits of silvopasture in the tropics," Nature Communications, Nature, vol. 13(1), pages 1-9, December.
    10. Djenontin, Ida N.S. & Ligmann-Zielinska, Arika & Zulu, Leo C., 2022. "Landscape-scale effects of farmers’ restoration decision making and investments in central Malawi: an agent-based modeling approach," LSE Research Online Documents on Economics 115672, London School of Economics and Political Science, LSE Library.
    11. Manan Bhan & Simone Gingrich & Sarah Matej & Steffen Fritz & Karl-Heinz Erb, 2021. "Land Use Increases the Correlation between Tree Cover and Biomass Carbon Stocks in the Global Tropics," Land, MDPI, vol. 10(11), pages 1-15, November.

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