Date Published: July 20, 2017
Publisher: Public Library of Science
Author(s): Catarina Conte Jakovac, Loïc Paul Dutrieux, Latifah Siti, Marielos Peña-Claros, Frans Bongers, RunGuo Zang.
Shifting cultivation is the main land-use system transforming landscapes in riverine Amazonia. Increased concentration of the human population around villages and increasing market integration during the last decades may be causing agricultural intensification. Studies have shown that agricultural intensification, i.e. higher number of swidden-fallow cycles and shorter fallow periods, reduces crop productivity of swiddens and the regrowth capacity of fallows, undermining the resilience of the shifting cultivation system as a whole. We investigated the temporal and spatial dynamics of shifting cultivation in Brazilian Amazonia to test the hypotheses that (i) agriculture has become more intensive over time, and (ii) patterns of land-use intensity are related to land accessibility and human population density. We applied a breakpoint-detection algorithm to Landsat time-series spanning three decades (1984–2015) and retrieved the temporal dynamics of shifting cultivation fields, which go through alternating phases of crop production (swidden) and secondary forest regrowth (fallow). We found that fallow-period length has decreased from 6.4 to 5.1 years on average, and that expansion over old-growth forest has slowed down over time. Shorter fallow periods and higher frequency of slash and burn cycles are practiced closer to residences and around larger villages. Our results indicate that shifting cultivation in riverine Amazonia has gone through a process of agricultural intensification in the past three decades. The resulting landscape is predominantly covered by young secondary forests (≤ 12 yrs old), and 20% of it have gone through intensive use. Reversing this trend and avoiding the negative consequences of agricultural intensification requires land use planning that accounts for the constraints of land use in riverine areas.
Tropical landscapes have been largely transformed by human land use. Shifting cultivation plays a central role in land cover transformation given its widespread occurrence in the tropics . Such landscapes are characterized by a mosaic of swiddens (temporary cropping fields) and fallows (temporary secondary forests) that are dynamic through space and time, and are mainly managed by slash and burn practices. Across the tropics, shifting cultivation systems have undergone expansion and intensification phases following public policies and socio-economic changes. From the 1960s to the 1980s, shifting cultivation was expanding over forests following government policies that stimulated the colonization of agricultural frontiers in Asia and Latin America . Subsequent public policies discouraged shifting cultivation practices and triggered, together with population increase and other socio-economic drivers, agricultural intensification and the replacement of swiddens for permanent land uses [3, 4].
In this study we assessed the dynamics of shifting cultivation fields over time using a novel remote sensing approach that allowed for high temporal and spatial resolution. Our data show that the expansion of swiddens over old-growth forest has slowed down in the last 30 years, and that swidden cultivation has been intensified, through the shortening of the fallow period. Our data support that the length of the fallow period is associated to access and suggests that constraints of land accessibility are encouraging agricultural intensification. These findings reveal that the dynamics of swidden cultivation is changing in Amazonia, possibly following recent socio-economic transformations in riverine livelihoods related to migration movements and market integration [13, 14].