Back to the future for the forests of Central Africa

Two of the authors, Jean Maley and Alex Chepstow-Lusty, summarize a recent paper in Quaternary Research for us.

A recent article in Quaternary Research1 by Jean Maley at the University of Montpellier and colleagues, which focuses on the scale of natural contraction and fragmentation of the rainforests across Central Africa 2500-2000 years ago, may have major implications for agriculture in this vulnerable region today. During this period, linked to global climate change, dry seasons became longer, and, combined with intensified storm activity, resulted in widespread erosion.

It has been proposed that this fragmentation 2500 years ago allowed the second and major phase of migration of Bantu-speaking peoples through the forests2, who were able to exploit pioneering trees, such as energy rich oil palms that had colonized the gaps created, as well as cultivate for the first time cereals in this newly created agricultural zone, including pearl millet (Pennisetum glaucum), for which archaeological evidence has been found.

This map in the paper indicates the extent of the forest refuges 2500 years ago, which were more resilient to climate change and hopefully shall remain so. The longer dry season, between 2500-2000 years ago, eliminated previous rainforests, and provided space for pioneer forests and savanna. Subsequently, after 2000 years ago, the rainforests grew back. In some regions, from south-eastern Cameroon to the northeast and east of the Congo Basin, a new forest formation developed, characterized by Gilbertiodendron dewevrei (‘Limbali’), a shade tolerant tree belonging to the Fabaceae-Caesalpinioideae. This canopy tree forms very dense, practically monospecific, evergreen stands in which the species regenerates well under its own shade. Nevertheless, some fragments of savanna have survived to this day as islands within the rainforest.

Map of forest refugia in Central Africa, 2500 BP

Recent meteorological data, including increased thunder and lightning activity, may already be suggesting that the climatic patterns leading to forest contraction and major erosion are starting again. Hence, the interval 2500-2000 years ago could provide a model for the future, with the savannas re-expanding (i.e. especially in the areas outside of the forest refuges). Previously, this occurred when human populations were negligible. That’s not the case now.

If predictions of an extended dry season become a reality, agriculturally a greater emphasis should probably be placed on the cultivation of African native cereals3, which maintain the characteristics of their wild savanna ancestors. Besides pearl millet, these include sorghum (Sorghum bicolor), finger millet (Eleusine coracana), fonio (Digitalis exilis and D. iburua) and African rice (Oryza glaberrima), and there should be less dependence on the relatively recent introductions and more demanding global cereals: wheat, rice and maize. Indeed, this approach could be essential for maintaining the production of arable lands in much of Central Africa and providing food security for an ever-growing population.

This paper brings together a range of data across a wide-geographical area, and should act as a wake-up call, with the implications for climate change, human activities and conservation already being experienced.

  1. Maley, J., Doumenge, C., Giresse, P., Mahé, G., Philippon, N., Hubau, W., Lokonda, M., Tshibamba, J., Chepstow-Lusty, A. (2017). Late Holocene forest contraction and fragmentation in central Africa. Quaternary Research, 1-17. doi:10.1017/qua.2017.97 []
  2. Bostoen, K., Clist, B., Doumenge, C., Grollemund, R., Hombert, J.M, Muluwa, J.K., Maley, J. 2015. Middle to Late Holocene paleoclimatic change and early Bantu expansion in the rain forests of Western Central Africa. Current Anthropology, 56 (3) : 354-384. []
  3. National Research Council. 1996. Lost Crops of Africa. Volume 1: Grains. National Academy Press. Washington D.C. []

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Celebrating Africa

Well, while we can all agree that living conditions in many places in Africa may not be up to the standard of the current President of the USA, that hasn’t stopped the continent producing some very remarkable women and men. I’ll just mention two from our field who have been in the news lately, one for a happy reason and one for a sad.

On the happy side, Dr Segent Kelemu, director general of ICIPE, was just featured by Bill Gates in the recent issue of Time magazine which he guest-edited:

Kelemu, 60, grew up in a small Ethiopian village with only one dress and no shoes to wear. She rebelled against the constraints placed on her as a girl. (They cracked.) Along the way, she has fostered a faith that each problem possesses a solution. Among her discoveries: “Life is always a lesson,” she says. “Every day, I learn from everybody.”

On a much sadder note, Harvard’s Prof. Calestous Juma passed away just before Christmas:

Africa, he wrote, contained 60% of the world’s available arable land. It also contained, in sharp contrast to monocultures elsewhere, a vast range of indigenous crops. Many of these, long adapted to arid conditions, could help feed the world despite climate change. Africa was a reservoir of biodiversity, and the next step was to ensure that the storing of seeds, and research into them, became the business of African governments, universities and farmers. Perhaps his most satisfying stint was as the first executive secretary of the UN convention on biodiversity of 1992—in effect an African safeguarder of that vast and endangered genetic library, still hardly catalogued and still largely unread.

Let’s celebrate them, and all the others too.