Mapping how deforested land in Africa is used

Africa’s forest areas – approximately 14% of the world’s forest area – continue to decline at an increasing rate, mainly due to human activities to convert forest lands for economic purposes. As natural forests are important in CO₂ and reservoirs of biodiversity, this development has a significant impact on climate change and affects the integrity of nature.

To intervene in a targeted manner in the interest of climate and biodiversity protection, there is a lack of sufficiently reliable data and detailed knowledge on the different forms of further use of deforested areas to know where conversions linked to deforestation occur. forest and why.

This is confirmed by a new study published in the journal Scientific reports and led by Robert N. Masolele and Johannes Reiche of Wageningen University in the Netherlands, Martin Herold of the GFZ German Research Center for Geosciences in Potsdam and their team.

They used high-resolution satellite data, which they analyzed against local reference data for 15 different types of land use – from crops like coffee, cashews and rubber to pastures and mines – using deep learning methods. This allowed them to create the first high-resolution (five-meter precision) continental mapping of land use after deforestation over a large area of ​​the African continent, including both wet and dry forests.

This provides an improved basis for improving transparency on areas where commodity expansion is leading to deforestation and to support strategic planning and implementation of deforestation mitigation measures by governments and agencies. protection of forests, both in Africa and in the EU, where a new EU regulation aims to establish “deforestation-free supply chains” for products made from certain raw materials.

Africa’s threatened forests and the European regulation on deforestation

Over the past two decades, Africa has experienced a rapid decline in forest areas and tree cover. How land use changes after deforestation has a significant impact on forest biomass, biodiversity and the water cycle.

These changes may vary depending on the location, intensity and spatial extent of forest loss. Understanding the spatio-temporal extent and patterns of deforestation in Africa is essential to understand and mitigate its contribution to greenhouse gas emissions and its negative impacts on the forest ecosystem.

The EU also wants to make an important contribution to reducing forest loss. The European Union Deforestation Regulation (EUDR) is a new initiative that aims to ensure that products placed on the EU market are free of deforestation and thus protect the world’s forests for future generations.

It also promotes transparency and traceability in supply chains, enabling consumers to make informed choices about the products they purchase.

Insufficient database to date

Although there are some national and regional statistics documenting trends in forest loss, there is a lack of consistent, detailed, and spatially explicit estimates and mapping of the factors responsible for forest loss. The available information is often based only on samples at specific times, is not available with sufficient spatiotemporal resolution and thematic classification, and so far only includes dry forests.

Interpretations often rely on visual inspection of satellite images and the historical expectation that different forms of subsistence agriculture persist and that certain land uses are limited to specific geographic locations. This does not take into account the diversity of the real causes of forest loss.

Global approach to mapping with high-resolution satellite data

In an extensive study, researchers led by Robert N. Masolele, a postdoctoral researcher at Wageningen University in the Netherlands, and Martin Herold, head of Section 1.4 “Remote Sensing and Geoinformatics” at the GFZ German Research Center for Geosciences and professor at the University of Potsdam, have now deciphered the complex land use patterns that emerge after deforestation across Africa’s diverse landscapes.

They present the first comprehensive map of land use after deforestation in Africa, covering forest loss from 2001 to 2020. The map is available with a spatial resolution of five meters and 15 land use classes: from crops such as cocoa, cashew, oil palm, rubber, coffee and tea to mines, roads, settlements, pastures, small and large scale agriculture, as well as to forest plantations and other land covered with trees.

On the one hand, the researchers relied on high-resolution Planet NICFI satellite data provided by Norway’s International Climate and Forest Initiative (NICFI). Accordingly, the study was conducted on the African continent between 30 degrees north latitude and 30 degrees south latitude and includes countries in West, Central, East and Southern Africa. Wet and dry forests characterize the region.

Second, they used reference data from various publications, some of which were obtained via crowdsourcing with the help of citizen science or other remote sensing campaigns and open data sources.

“What makes this study special is the innovative use of satellite imagery, machine learning algorithms and active learning. This allowed us to accurately identify land use after deforestation, map it at an unprecedented scale and level of detail, and assess the trend and hotspots. of land use conversion in different countries and regions of Africa,” explains Robert N. Masolele, lead author of the study.

The most important results on land use in Africa

The study reveals a complex network of land uses that emerge after deforestation events. It shows that the causes of forest loss vary from region to region. In general, small-scale croplands are the main driver of forest loss in Africa, with hotspots in Madagascar and the Democratic Republic of Congo.

Furthermore, commodity crops such as cocoa, oil palm and rubber are the main drivers of forest loss in the rainforests of West and Central Africa, forming an “arc of commodity expansion” in this region. At the same time, cashew hotspots increasingly dominate the dry forests of West and Southeast Africa, while larger hotspots for large-scale croplands have been found in Nigeria and Zambia.

The increased expansion of cocoa, cashew, oil palm, rubber and large-scale croplands observed in the humid and dry forests of West and Southeast Africa suggests that these lands are vulnerable to future land use changes related to staple crops.

Ranking and outlook

Although the mapping is extensive, the study recognizes that it is difficult to classify some forms of land use with a high degree of precision. Factors such as cloud cover and seasonal variations present limitations that highlight the need for continued refinement and validation.

“The study makes a crucial contribution to our understanding of the complex interaction between human economic activities and the environment. Its particular importance lies in providing policy makers, environmental advocates and scientists a detailed understanding of the different developments that land in large parts of Africa undergoes following deforestation.

“This knowledge is crucial for developing targeted conservation strategies, achieving sustainable development goals and mitigating the environmental impacts of deforestation on the African continent,” emphasizes Martin Herold. “We in Europe will also benefit, as new EU deforestation regulations require proof of deforestation-free supply chains for certain raw materials such as coffee, cocoa and rubber.”

Overall, this new study shows the great potential of using high-resolution satellite data, combined with artificial intelligence and regional knowledge, to provide open source information to different stakeholders and improve monitoring transparency critical land use transitions linked to tropical forests. .