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. 2020 Nov;587(7832):78-82.
doi: 10.1038/s41586-020-2824-5. Epub 2020 Oct 14.

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

Martin Brandt  1   2 , Compton J Tucker  3 , Ankit Kariryaa  4   5 , Kjeld Rasmussen  6 , Christin Abel  6 , Jennifer Small  4   7 , Jerome Chave  8 , Laura Vang Rasmussen  6 , Pierre Hiernaux  4   9 , Abdoul Aziz Diouf  10 , Laurent Kergoat  11 , Ole Mertz  6 , Christian Igel  12 , Fabian Gieseke  12   13 , Johannes Schöning  5 , Sizhuo Li  6 , Katherine Melocik  4   7 , Jesse Meyer  4   7 , Scott Sinno  4   7 , Eric Romero  4   7 , Erin Glennie  4   7 , Amandine Montagu  14 , Morgane Dendoncker  15 , Rasmus Fensholt  6
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An unexpectedly large count of trees in the West African Sahara and Sahel

Martin Brandt et al. Nature. 2020 Nov.

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.

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References

    1. Bayala, J., Sanou, J., Teklehaimanot, Z., Kalinganire, A. & Ouédraogo, S. Parklands for buffering climate risk and sustaining agricultural production in the Sahel of West Africa. Curr. Opin. Environ. Sustain. 6, 28–34 (2014). - DOI
    1. Stringer, L. C. et al. Challenges and opportunities in linking carbon sequestration, livelihoods and ecosystem service provision in drylands. Environ. Sci. Policy 19–20, 121–135 (2012). - DOI
    1. Schnell, S., Kleinn, C. & Ståhl, G. Monitoring trees outside forests: a review. Environ. Monit. Assess. 187, 600 (2015). - DOI - PubMed
    1. LeCun, Y., Bengio, Y. & Hinton, G. Deep learning. Nature 521, 436–444 (2015). - DOI - PubMed
    1. Darkoh, M. B. K. The nature, causes and consequences of desertification in the drylands of Africa. Land Degrad. Dev. 9, 1–20 (1998). - DOI

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