アフリカ熱帯雨林における狩猟採集生活の生態基盤の再検討

－野生ヤムの利用可能性と分布様式から－

抄録

The availability of wild yams (Dioscorea spp.) has been considered the key factor that determines the viability of hunting and gathering as a way of life in the African rainforests. Annual-stem yams (D. praehensilis and D. semperflorens) in particular are the most reliable resource to support ample subsistence by foraging during the dry season, which has been considered to be extremely severe for a “pure” foraging life in tropical forests. An analysis of the canopy photographs indicates that “annual” yams favor habitats with sunlight, namely, forest gaps. The “annual” yams were, however, observed only in the limited areas presently situated far from the village, while forest gaps were omnipresent throughout the forest. The propagation of the “annual” yams thus seems to be restricted under natural conditions.

An old map printed in 1910 during the German rule shows that there had been in the area several village sites of the Bantu cultivators; and this fact suggests Baka camps were probably also distributed around these villages. Although the Bantu cultivators, who depended on bananas and cassavas, might have not grown wild yams in their fields, it is possible that the Baka made a positive impact on the formation of patches of plenty of “annual” yams, for example, through transplanting heads of yams into favorable habitats. If such a manner of “semi-cultivation” substantially increased the opportunity for the formation of yam patches, the framework of examination of the ecological bases of human subsistence of the African rainforests should be reconsidered.