Ecology of the past

I am delighted to be able to report that Alfred Houngnon (University of Abomey-Calavi, Benin) has been awarded an INQUA Fellowship for 2024 to develop his research into past environmental change in the Dahomey Gap. This research will link up my laboratory, at the Institute of Biodiversity & Ecosystem Dynamics (University of Amsterdam), and the group of Dr Mireille S.S. Toyi (Laboratory of Applied Ecology, University of Abomey-Calavi). Below, and in the associated video report, Alfred explains the project and what he hopes to achieve during the project.

The Dahomey Gap project is designed to gain new insights on the West African palaeoenvironments using pollen, charcoal and dung fungal spore records to reconstruct past vegetation, fire and animal abundances. These empirical data will then be compared against paleoclimate models. Specifically, we will explore the interactions between fire, animals and vegetation around the Ewe-Adakplame forest in the south east of Benin Republic and highlight the role humans would have previously played in the modification of the landscape for millennia.

The Ewe-Adakplame forest is an emblematic and heritage community reserve that covers about 500 hectares serving as single habitat for 17% of national flora including many range restricted heritage African trees. The study site belongs to the Dahomey Gap, a 200 kilometers forest‐savanna corridor between Ghana, Togo, Benin and Nigeria that splits the African rainforest into the Guinean and Congolean blocks. The blocks are defined as the Guineo-Congolian Regional Centre of Endemism including three sub-centres : Upper Guinea, Lower Guinea, and Congolian, each with distinctive endemic flora. This region is especially interesting because it contains a mosaic of ecosystems, including isolated and persistent island forests. In the Benin Republic the island forests, within the savanna landscape, are the last forest habitats which preserve the biological heritage of the country, and represent an important part of the national floristic diversity and therefore have a high conservation priority. The Ewe-Adakplame forest is an exciting case that could probably reflect the “memory of the past” and provide a unique perspective for palaeoecology in the context of human-environment interactions and climate changes.

Although still widely debated, some palaeoclimatic models suggest that through the termination of the African Humid Period, West Africa was relatively stable in terms of climate (precipitation and temperature). This seems to contradict the hypothesis of an abrupt drying causing the formation of the Dahomey Gap. Obviously, African ecosystems have experienced a long history of climate change and human settlement particularly with agricultural practices, fire use, livestock and the development of iron work. Therefore, in this project we will test the idea that human activity was primarily responsible for the loss of forest in the Dahomey Gap since 4500 years ago by reconstructing the key ways in which humans modified the landscape (changing fire regimes and introducing animals), and relating this change to the vegetation change.

Two to 3 meters long sediment cores will be recovered from lakes around the Ewe-Adakplame forest. The age of the sediments will be determined using radiocarbon dating. Sediments will be subsampled and analyzed for pollen, charcoal, and dung fungal spores. Pollen data will be used to provide insights into past vegetation. To ensure the best possible interpretation of the fossil pollen data, modern pollen traps will be deployed locally for one year to capture the modern pollen rain. Fire regime will be characterized through analysis of charcoal recovered from the sediments, and herbivory will be assessed through the analysis of coprophilous fungal spores. The results will help to reassess the role of past peoples in the formation of the Dahomey Gap and raise awareness among scientists’ and locals on palaeoecology interest for landscape management and conservation.

We thank INQUA to have given us this great opportunity for an inspiring career in Palaeoecology in Africa.