Period: 15 January 2005 - 31 March 2005. Country: Cameroon
(1) An Ecological History of the African Rainforests: With Special Reference to the Exploitation of Yams (Dioscorea spp.) among the Baka Hunter-Gatherers of the Northwest Congo Basin
YASUOKA Hirokazu  (Division of African Area Studies)
Key Words: Ecological History, Baka Hunter-gatherers, Rainforest, Dioscorea spp., Congo Basin

Photo 1:A woman digs a tuber of wild yam (Dioscorea semperflorens)
Photo 2:An old couple harvests 30 kg of yam tuber (Dioscorea praehensilis) in a day
(2) It is not easy to give a perfect answer to the question of how tropical rainforests are related to human inhabitants, since rainforests are composed of variety of vegetations. Not only that, but the relationships between humans and nature in rainforests are characterized by diversity and multiplicity. The purpose of my Ph. D. dissertation is thus to examine the potential of tropical rainforests as human habitats, by drawing up an ecological history of the African rainforests with special reference to the exploitation of yams among the Baka hunter-gatherers of the Northwest Congo Basin.

(3) I conducted my field research in the village of Zoulabot Ancien in the East province of Cameroon, from 20 February to 31 March 2005, following the joint workshop with WWF-Cameroon on 16 February.
          In a previous paper I described the long-term foraging expeditions (molongo) of the Baka hunter-gatherers. In the dry season they go to an area containing many gathering spots that are abundant with some types of yams. These areas can be called “yam patches.” Based on an analysis of energy intake, I concluded that they can procure sufficient energy from yams even in the dry season, when energy sources become extremely scarce in the tropical rainforests.  The purpose of the present research is, accordingly, to search for a perspective to examine the extent and density of the distribution of yam patches in order to illustrate an ecological history of the wider area.
         During the present research, I paid attention to different characteristics among yam species. Between fifteen and seventeen species of yam (genus Dioscorea) and yam-like plants (genus Dioscoreophyllum) grow in the forest areas of Cameroon. Although I observed tubers of eight species being exploited by the Baka during the molongo period, D. praehensilis and D. semperflorens tubers accounted for 90% of energy intake from yams, and for 60% of the total energy intake. Both yams have annual stems and annual tubers. The tubers’ reserves reach a maximum in the dry season, and they become thin when they begin to sprout aerial stems at the beginning of the rainy season. This kind of yams prefers disturbed areas (gaps) of the forest so that the stems can rapidly reach the canopy in order to establish a photosynthetic surface.  D. praehensilis and D. semperflorens grow in clusters in these yam patches. The Baka therefore harvest considerable amounts of tubers when they find a yam patch.
         From the present research, I discovered that the yam patches were unevenly distributed in the forest: they were distributed aggregately in the area 30-40 km away from the village, and there were few yam patches around the village. Furthermore, there were several villages in the area containing many yam patches. Consequently, the inhabitants of the villages must have exploited the forest to some extent, and their activities seem to have, consciously or unconsciously, influenced the dynamics of the yam patches. Although many factors should be examined before making a complete model of the dynamics of yam patches, I have solid grounds for analyzing the dynamics of yam patches, focusing on the influence of human activities.

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