A fresh look at shifting cultivation: Fallow length an uncertain indicator of productivity

Abstract

Shifting cultivation is practiced by millions of farmers in the tropics and has been accused of causing deforestation and keeping farmers in poverty. The assumed positive relationship between fallow length and crop yields has long shaped such negative opinions on the sustainability and environmental impact of the system, as population growth is believed inevitably to lead to its collapse. Empirical evidence for this assumption is scarce, however, and a better understanding of system dynamics is needed before discarding shifting cultivation as unsustainable. With cases from Malaysia and Indonesia, we show that fallow length is a weak predictor of crop yields, though interactions with fertilizer inputs may increase its importance. Other factors such as drought, flooding, and pests are more important determinants of yields. The implication is that when using natural fallow as the only means of nutrient supply, there is no need to cut old fallow vegetation. Moreover, there is no evidence of system collapse, even at short fallow periods. We conclude that shifting cultivation should be accepted as a rational land use system and that earlier calls for bringing a ''Green Revolution'' to shifting cultivators are still relevant to achieve intensive and sustainable production.

The role of Amazonian anthropogenic soils in shifting cultivation: learning from farmers’ rationales

“…Relationships between fallow development, labor, and yields appeared early in the shifting cultivation literature (Nye and Greenland 1960, Boserup 1965, Clarke 1976, although these have not been thoroughly addressed with empirical measurements (Mertz 2002, Nielsen et al 2006, Mertz et al 2008. We provide evidence from local rationales that the reading of the fallow is a major source of information upon which farmers rely to make their decisions in shifting cultivation.…”

Representing anthropogenic gross land use change, wood harvest, and forest age dynamics in a global vegetation model ORCHIDEE-MICT v8.4.2

“…In tropical regions, fallow lengths in shifting cultivation range from 10 to 40 years (Bruun et al, 2006;Mertz et al, 2008;Thrupp et al, 1997;van Vliet et al, 2012), with a tendency of reduction in fallow length. In Latin American tropics, agricultural abandonment has already led to prominent growth of secondary forests (Chazdon et al, 2016;Poorter et al, 2016).…”

“…But when this is not possible because of inevitable mismatch between the model and forcing data, harvest areas of primary and secondary forests could mutually compensate for each other in the model to ensure that their prescribed total harvest area remains realized. A number of studies reported that fallow lengths for shifting cultivation could range from a few years to more than 50 years depending on different regions, with the majority being 10-40 years (Bruun et al, 2006;Mertz et al, 2008;Thrupp et al, 1997;van Vliet et al, 2012), and there is a tendency in reduction of fallow lengths possibly because of increased population pressure (van Vliet et al, 2012). Hurtt et al (2011) assumed a mean residence time of 15 years for shifting cultivation for tropical regions in the LUH1 reconstruction data.…”

An essay on the Boserupian model with particular emphasis on labour input and productivity in upland rice swiddens in Southeast Asia

“…The focus of the present study is on labour input rather than on yield. The relationship between yield and fallow periods of upland rice in Southeast Asia has already been quantitatively discussed in several other studies (Cramb 1984, Mertz 2002, Bruun et al 2006, Mertz et al 2008. Before the abovementioned discussion begins, the section that follows proposes a mathematical expression to capture the process of the shortening of fallow periods with population growth.…”