Rethinking the relationship between length of fallow and crop yields in shifting cultivation? The theory that a correlation between shortened fallow periods and yield decline in shifting cultivation exists is questioned in this paper. This relationship has been taken for granted, and because it shows that shifting cultivation will break down under pressure, it has partly been responsible for negative government views on shifting cultivation. Yield levels in shifting cultivation are influenced by a wide range of biophysical, socioeconomic, and cultural factors and it is difficult to isolate fallow length as a single determining factor. A total of 330 studies were reviewed and fifteen with empirical data were chosen for in-depth analysis. Although most of the empirical studies support the theory, the data sets are often ambiguous and important parameters are insufficiently taken into account. Several studies found no relationship between fallow length and yield, but these also lack information to verify the validity of the data. It is concluded that empirical studies focussing on this problem are needed to fully understand this relationship and develop feasible scenarios for the numerous attempts at modelling shifting cultivation development. Moreover, the use of gloomy 'breakdown' scenarios as justification for improving shifting cultivation should be avoided.
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