Environmental change in the Sahel, Research results

Tree cover promoted in semi-arid Sahelian farms – new publication in Nature Geoscience

More people equal more trees in semi-arid West Africa – Our new study published in Nature Geoscience questions ‘received wisdom’ as concerns the relationship between human agency and woody vegetation of West Africa. We demonstrate that in low-rainfall areas woody cover is denser in cultivated areas than in savannas, and close to settlements rather that further away, thus rejecting simplistic Malthusian ideas of a negative relationship between population density and woody cover.

These findings challenge the traditional view on agricultural expansion in semi-arid lands and this has implications for the understanding of effects of agricultural expansion on ecosystem services, including carbon sequestration. Also, these findings throw light upon the process of land degradation/desertification which contradicts commonly believed narratives on human expansion in drylands causing fuel-wood crisis, deforestation, soil depletion, erosion and desertification.

 The study is part of an unprecedented NASA project (lead by CJ Tucker), which aims at applying commercial DigitalGlobe satellite imagery with a spatial resolution of 50 cm to map the size of each individual tree and shrub in African dryland ecosystems. Our team had access to thousands of these images, and this study is the first allowing a wall-to-wall map of woody cover based on individual trees.

In contrast to traditional case studies prone to sampling errors and bias by the prevailing societal discourse, the woody cover map includes 40,000 villages, passing a technical tipping point in dryland environmental research.

Article in Nature Geoscience:

Brandt, M., Rasmussen, K., Hiernaux, P., Herrmann, S., Tucker, C.J., Tong, X., Tian, F., Mertz, O., Kergoat, L., Mbow, C., David, J.L., Melocik, K.A., Dendoncker, M., Vincke, C., Fensholt, R., 2018. Reduction of tree cover in West African woodlands and promotion in semi-arid farmlands. Nature Geoscience 1. https://doi.org/10.1038/s41561-018-0092-x

Further read in Nature Geoscience News (summary by Niall Hanan):



Research results

A new tool to monitor aboveground vegetation carbon stocks: first application to the African continent

Our new study uses unprecedented data sources to measure vegetation carbon stock dynamics at continental scale. The study demonstrates that over the African continent, the net carbon balance is negative for 2010-2016, and that most of the carbon losses occurred in dryland savannahs. The results were published in the journal Nature Ecology and Evolution.

The African continent is facing one of the driest periods in the past three decades as well as continued deforestation. These disturbances from both human pressure and climate change threaten vegetation carbon stocks and highlight the need for improved capabilities of monitoring large-scale aboveground carbon stock dynamics.

Continental scale monitoring of vegetation carbon dynamics requires satellite based techniques, however, conventional satellites are limited to sensing the upper canopy layer. Consequently, the monitoring of vegetation dynamics is limited to the top green parts of the canopies which are not directly linked to aboveground biomass carbon.

Our French colleagues around Jean Pierre Wigneron (CEA, CNES, CNRS, INRA) have produced a new data set retrieved from space-borne observations of the SMOS satellite starting in 2010. The data set is based on low frequency passive microwave emissions, which are insensitive to cloud cover and green vegetation and thus able to quantify aboveground biomass carbon of the entire vegetation layer, including stems and branches, even when the vegetation is dense.

Our group had the chance to be the first group testing these new data, with groundbreaking results. For the first time, scientists were able to monitor large scale carbon stock dynamics at annual scale. The groups expect this tool to be a key in future monitoring of carbon losses and gains for national reports and large-scale efforts, such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC).

A first application to the African continent showed highly dynamic carbon stocks, and especially dryland savannahs showed surprisingly high gross losses which were caused by recent drought years. The study concludes that the new tool is close to be operational and highlights the importance of drylands in the global carbon balance.

Screenshot from 2018-03-27 15-03-42.png
Changes in aboveground vegetation carbon stocks in sub-Saharan Africa over 2010–2016. Regions with significant negative (carbon source) or positive (carbon sink) carbon changes are shown, respectively, in red or green.

© M. Brandt – Université de Copenhagen

Article at Nature Ecology and Evolution:

Brandt M, Wigneron J-P, Chave J, Tagesson T, Penuelas J, Ciais P, Rasmussen K, Tian F, Mbow C, Al-Yaari A, Rodriguez-Fernandez N, Schurgers G, Zhang W, Chang J, Kerr Y, Verger A, Tucker C, Mialon A, Rasmussen LV, Fan L, Fensholt R. 2018. Satellite passive microwaves reveal recent climate-induced carbon losses in African drylands. Nature Ecology & Evolution 1. DOI: 10.1038/s41559-018-0530-6

Further reading:

Mongabay: new remote sensing technique used to determine carbon losses in sub-saharan africa

Article at Carbon Brief



Why our research matters

At some point, many scientists working in geographic fields may have asked themselves if there is any “use” in the work we do. The main aim of a study should not be to get it published in a high impact journal but to share research results with as many people as possible. However, here comes the dilemma, high impact journals are recognized by a much wider audience, so in the end it does matter where the study is published. Our paper just published in Nature Sustainability made it into the News and Views section of Nature with the nice title “Satellite images show China going green“. It is a great summary of our work and helps to reach an even larger audience.

So what makes this work so attractive? The human footprint in satellite images is traditionally linked with degradation, conversion of forest areas into farmlands or urban areas and air pollution. Especially large population countries with a boosting economy, like China, are usually linked with the destruction of the environment. However, here we show that management and conservation activities in China can lead to a large increase in vegetation cover and carbon stocks, in spite of drought conditions. The observed increase in vegetation growth does not only improve the ecological environment by alleviating degradation, but also the magnitude of increase is found to be large enough to contribute to a greening Earth and store large amounts of carbon.

We are happy that this message made it into the Nature News section, which is certainly among the top places where scientific results can end up. It is a nice confirmation that what we do does matter and is recognized at highest levels.

Macias-Fauria, M. (2018). Satellite images show China going green. Nature, 553(7689), 411. https://doi.org/10.1038/d41586-018-00996-5

New Publication in Nature Sustainability

Now this is something really cool:
-We have a paper in the first ever issue of the new journal Nature Sustainability
-Both the cover of the first issue and the website banner are my photos I shot last summer in Southern China
-The paper is the thesis of my girlfriend and it is the cover story!

Screenshot from 2018-01-16 21-06-23

Screenshot from 2018-01-16 21-01-59The paper is super interesting and very nice to read:

Xiaowei Tong, Martin Brandt, Yuemin Yue, Stephanie Horion, Kelin Wang, Wanda De Keersmaecker, Feng Tian, Guy Schurgers, Xiangming Xiao, Yiqi Luo, Chi Chen, Ranga Myneni, Zhen Shi, Hongsong Chen, Rasmus Fensholt. Increased vegetation growth and carbon stock in China karst via ecological engineering. Nature Sustainability 1.


How does conflict affect land use? New publication!

Population and Environment in the Middle East

In November 2015, me and a colleague (Michael Degerald, visit his blog here) asked the question: how is agriculture affected in the areas seized by the Islamic State (aka ISIS, ISIL, Da’esh)? We couldn’t find much information to answer our question, so we decided to investigate it ourselves.

At first we wanted to look at changes in productivity indicated by satellite measured greenness, but later we decided to go a step deeper and look at land use activity as an indicator of land abandonment (as I had done in a previous publication). As the project moved on, more people became interested, and eventually three more co-authors were added: Petter Pilesjö (Lund University), Martin Brandt and Alexander Prishcepov (both from Copenhagen University).

Together, we conducted a land use classification based on NDVI data from MODIS based on the seasonality of the land surface. We distinguished between single cropped cropland…

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Expanding the study area: from West Africa to South China

People who know me and my research know that I am in love with the Sahel and its people, and this will never change. However, I recently had the chance to expand my research area from the semi-arid Sahel to humid China, more specifically the South China Karst. I spent around 4 months in China in 2017, and there are some major publications on the way. This area is particularly interesting, because millions of trees have been planted, and while we have a hard time to find a human footprint in satellite data over Sahel, it is more than obvious in China. It is also a very beautiful area:


Our research in the media

Our article in Nature Ecology & Evolution got some media attention, both in the Danish and the international press.

Here is our article:

Brandt, M.; Rasmussen, K.; Peñuelas, J.; Tian, F.; Schurgers, G.; Verger, A.; Mertz, O.; Palmer, J. R. B.; Fensholt, R. Human population growth offsets climate-driven increase in woody vegetation in sub-Saharan Africa. Nature Ecology & Evolution 2017, 1, 0081.