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 -