Ecological Factors of the Recently Expanding Style of Shifting Cultivation in Southeast Asian Subtropical Areas : Why Could Fallow Periods Be Shortened?

Abstract

In Southeast Asian subtropical areas, fallow periods of shifting cultivation have shortened, and fallow vegetation has changed from forest to herbaceous meadow. It is widely believed that traditional farming systems have collapsed from the pressure of rising population, but the author considers this doubtful. The author investigated the ecological factors that enabled the newly expanding style of shifting cultivation in Xishuangbanna, Southwest China, to offer a counterargument to the hypothesis that untraditional styles of shifting cultivation are all unsustainable. Nine months after Eupatorium odoratum L., a perennial herb that invaded from South America, was removed from fallow fields, the most harmful perennial grass, Imperata cylindrica (L.) P. Beauv., was dominant. When water buffaloes were excluded from fallow fields for four years, Imperata cylindrica also became dominant. It was concluded that the newly expanding style of shifting cultivation is a rational adaptation to the invasion of the herbaceous perennial plant Eupatorium odoratum. Perennial grasses, especially Imperata cylindrica, the control of which is the most important factor determining fallow duration, are quickly excluded by the combination of Eupatorium odoratum and buffalo grazing. This explains why fallow periods could be shortened. In the farming system observed today, the selective herbicide 2-4-D greatly helps to reduce weeding labors. In addition to ecological factors, easier access to the market has also caused the successive changes in farming systems.