小柯机器人

丹麦哥本哈根大学Martin Brandt和美国国家航空航天局戈达德太空飞行中心Compton J. Tucker研究小组，合作绘制了西非撒哈拉和萨赫勒地区树木的覆盖情况。2020年11月14日，《自然》在线发表了这项成果。

研究人员使用亚微米分辨率的卫星图像和深度学习方法，绘制了西非撒哈拉、萨赫勒地区和半湿润地区130万平方公里土地上占地面积超过3平方米树木的树冠大小。研究人员检测到超过18亿棵树木（每公顷13.4棵树），树冠中位数为12平方米，每年的降雨梯度为0到1,000毫米。冠层覆盖率从高干旱地区的0.1％（每公顷0.7棵树）增加到干旱地区的1.6％（每公顷9.9棵树）、半干旱地区的5.6％（每公顷30.1棵树）和半湿地地区的13.3％（每半公顷47棵树木）。

尽管树冠的总覆盖率很低，但单独树木相对较高的密度挑战了主流有关旱地荒漠化的说法，甚至沙漠地区也具有惊人的高树木密度。该评估提出了一种监测全球森林以外树木的方法，并探索其在减轻土地退化、气候变化和贫困中的作用。

据悉，大部分旱地树木和灌木（以下统称为树木）都是孤立生长的，没有遮掩。这些非森林系统在生物多样性中具有至关重要的作用，并提供生态系统服务，例如碳储存、粮食资源以及人和动物的庇护所。但是，大多数与树木有关的研究都集中在森林上，而森林外的树木则没有充分的文献记载。

附：英文原文

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

Author: 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, Ole Mertz, Christian Igel, Fabian Gieseke, Johannes Schning, Sizhuo Li, Katherine Melocik, Jesse Meyer, Scott Sinno, Eric Romero, Erin Glennie, Amandine Montagu, Morgane Dendoncker, Rasmus Fensholt

Issue&Volume: 2020-10-14

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 desertification5,6,7, 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.

DOI: 10.1038/s41586-020-2824-5

Source: https://www.nature.com/articles/s41586-020-2824-5

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