(3) From Jan. 15, 2005 to Feb. 15, 2005, I conducted fieldwork in Kifanya Village, Njombe District in the Iringa Region of Tanzania. In recent years, the Bena people have planted black wattle trees (Acacia mearnsii) to use as charcoal and pine trees (Pinus patula) for timber on fallow hillside fields. They fell and use these trees after 10 to 20 years, and burn the remaining branches and leaves, making cultivation possible with little or no chemical fertilizer. Through my research, (I) I elucidated the historical relations of tree planting, lumbering and slash-and-burn cultivation. And (II), I collected soil samples from various stages of the fallow and cultivation process from hillside fields, in order to analyze annual changes in soil fertility resulting from the growth of trees and burning of the fields.
(I) In my earlier research, conducted in 2000, I found that slash-and-burn cultivation fields were usually prepared on cutover areas of black wattle forest. However, these fields are currently prepared mainly on cutover areas of pine forest. This change was caused by the following factors: (1) The Bena began to actively plant pine trees after the 1980s, and many pine forests planted at that time have become mature. (2) The introduction of diesel-powered table saws as a substitute for pit saws led to an increase in sawing speed, resulting in an expansion of the cutover area of pine forests.
(II) I am currently analyzing soil samples. The two following points were clarified: (1) The soil under the pine forests is strongly acidic. (2) However, ash from the burnt vegetation can neutralize soil acidity.
Based on these findings, I will evaluate how the changes in the Bena cultivation system relate to changes in their society.