TY - JOUR

T1 - An unexpectedly large count of trees in the West African Sahara and Sahel

AU - Brandt, Martin

AU - Tucker, Compton J.

AU - Kariryaa, Ankit

AU - Rasmussen, Kjeld

AU - Abel, Christin

AU - Small, Jennifer

AU - Chave, Jerome

AU - Rasmussen, Laura Vang

AU - Hiernaux, Pierre

AU - Diouf, Abdoul Aziz

AU - Kergoat, Laurent

AU - Mertz, Ole

AU - Igel, Christian

AU - Gieseke, Fabian

AU - Schöning, Johannes

AU - Li, Sizhuo

AU - Melocik, Katherine

AU - Meyer, Jesse

AU - Sinno, Scott

AU - Romero, Eric

AU - Glennie, Erin

AU - Montagu, Amandine

AU - Dendoncker, Morgane

AU - Fensholt, Rasmus

PY - 2020

Y1 - 2020

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85092592991&partnerID=8YFLogxK

U2 - 10.1038/s41586-020-2824-5

DO - 10.1038/s41586-020-2824-5

M3 - Journal article

C2 - 33057199

AN - SCOPUS:85092592991

VL - 587

SP - 78

EP - 82

JO - Nature

JF - Nature

SN - 0028-0836

ER -