Sub-continental-scale carbon stocks of individual trees in African drylands

Abstract: (Nature Paper)
The distribution of dryland trees and their density, cover, size, mass and carbon content are not well known at sub-continental to continental scales. This information is important for ecological protection, carbon accounting, climate mitigation and restoration efforts of dryland ecosystems. We assessed more than 9.9 billion trees derived from more than 300,000 satellite images, covering semi-arid sub-Saharan Africa north of the Equator. We attributed wood, foliage and root carbon to every tree in the 0–1,000 mm year−1 rainfall zone by coupling field data19, machine learning, satellite data and high-performance computing. Average carbon stocks of individual trees ranged from 0.54 Mg C ha−1 and 63 kg C tree−1 in the arid zone to 3.7 Mg C ha−1 and 98 kg tree−1 in the sub-humid zone. Overall, we estimated the total carbon for our study area to be 0.84 (±19.8%) Pg C. Comparisons with 14 previous TRENDY numerical simulation studies for our area found that the density and carbon stocks of scattered trees have been underestimated by three models and overestimated by 11 models, respectively. This benchmarking can help understand the carbon cycle and address concerns about land degradation. We make available a linked database of wood mass, foliage mass, root mass and carbon stock of each tree for scientists, policymakers, dryland-restoration practitioners and farmers, who can use it to estimate farmland tree carbon stocks from tablets or laptops.

Bios:
Compton Tucker, a native of Carlsbad New Mexico, received his B.S. degree in biological science in 1969 from Colorado State University in Ft. Collins. After working for Colorado National Bank in Denver and the First National Bank in Albuquerque, he returned to Colorado State University for graduate school in Earth science. He received his M.S in 1973 and his Ph.D. in 1975, both from the College of Forestry. In 1975, he came to NASA/Goddard as a National Academy of Sciences post-doctoral fellow, and in 1977 became an employee of NASA. At NASA/Goddard, Tucker has used satellite data to study the Earth, in research areas that include famine early warning, deforestation, desert boundary determination, ecologically-coupled diseases, terrestrial primary production, food security, and identifying degraded lands. Since 2015, he has devoted most of his time complimenting NASA satellite observations with commercial satellite data. He took part from 2002 to 2012 in NASA’s Space Archaeology Program, leading a group that assisted archaeologists mapping ancient sites with ground-penetrating radar and magnetometry in Turkey, at the sites of Troy of Trojan War fame, in the Granicus River Valley, and at Gordion, the home of King Midas.

He has authored or coauthored more than 220 journal articles that have been cited more than 32,000 times according to the Web of Science and more than 87,000 time according to Google Scholar. He has a Google Scholar index of 130 and a Google Scholar index since 2018 of 72. He is an adjunct professor at the University of Maryland and is a consulting scholar at the University of Pennsylvania’s Museum of Archaeology and Anthropology. He taught "Introduction to Remote Sensing" seven times at the University of Maryland, which forced him to learn the subject better. He has appeared on more than forty radio and TV programs. He is a Fellow of the American Geophysical Union & the American Association for the Advancement of Science. He has been awarded several medals and honors, including NASA’s Exceptional Scientific Achievement Medal, the Pecora Award from the U.S. Geological Survey, the National Air and Space Museum Trophy for Current Achievement, the Henry Shaw Medal from the Missouri Botanical Garden, the Galathea Medal from the Royal Danish Geographical Society, the Vega Medal from the Swedish Society of Anthropology and Geography, and the Mongolian Friendship Medal.

Pierre Hiernaux: agricultural engineer (National Agronomy School in Montpellier, France, 1970), Doctor in vegetation ecology (University of Montpellier, 1975), specialized in vegetation ecology applied to natural resource management, Pierre Hiernaux has 45 years of professional experience in tropical Africa. He has authored or co-authored over 250 publications, with an emphasis on plant ecology and range resource survey, on mapping and remote sensing applied to resources monitoring, on rangeland productivity, dynamics and management, and on the functioning and bio-economic modelling of agricultural systems. Pierre Hiernaux is a retired researcher, independent consultant (PASTOC), member of the French Scientific Committee on Desertification. In previous employments he served as scientist at the International Livestock Center for Africa (ILCA, Addis Ababa) based in Mali from 1975 to 1993, then at the International Livestock Research Institute (ILRI, Nairobi) based in Niger from 1993 to 2002. Guest professor at the University of Hohenheim in Germany from 2003 to 2004, he move to Toulouse in France, first at the Centre for Spatial Studies of the Biosphere (CESBIO) under contract with the University Paul Sabatier from 2005 to 2009, then to the Geoscience Environment Toulouse (GET) laboratory as a CNRS scientist from 2010-2014.

Ankit Kariryaa received his PhD from the University of Bremen, Germany in 2020. Since then he works as a postdoc at the Machine Leaning Section, Department of Computer Science, University of Copenhagen. His research focuses on the development of deep learning methods for large-scale monitoring of vegetation dynamics and other ecosystem properties using very-high resolution satellite imagery. Ankit enjoys playing chess, reading novels, and sailing in his free time.

Summary