Is forest or Ecological Transition taking place? Evidence for the Semiarid Chaco in Argentina

Abstract

The expression Forest Transition (FT) and Ecological Transition (ET) were coined to describe the recovery path of forested areas (or more general natural vegetation) after heavy conversion into croplands. FT/ET would be driven by two main socio-economic controls: a) agricultural intensification in the most productive areas and the simultaneous reduction of cropped area in the less suitable areas (land-sparing); and b) rural population migration from rural to urban areas. In the argentine portion of the Semiarid Chaco a rapid and extensive clearing for industrial agriculture and cattle ranching based on sown pastures is taking place. In this article we evaluated the occurrence, magnitude and localization of FT/ET in the argentine portion of the Semiarid Chaco during the 1977–2007 period using an approach based on remotely sensed data. From land cover maps we derived three diagnosis variables of FT/ET: (1) the area of natural vegetation at the end of the study period; (2) the rate of annual clearance (natural vegetation loss) for the whole period; and (3) the temporal change of the area of natural vegetation in the last portion of the study period. The diagnosis variables were combined to derive 12 classes (landscape types). We observed a systematic loss of the surface occupied by natural vegetation. Industrial agriculture grew in aggregated patches generating a homogenization of the landscape. In only a 4.8% of the study area we observed a pattern of change compatible with a FT/ET. In contrast, in a 34% of the study region (9.57 million ha) a clear negative trend in the cover of natural vegetation was observed during 1977–2007 period. The area that had a negative trend in the cover of natural vegetation was 7 times greater than the portion of the region experiencing positive trends. Such number indicates an imbalance in the landscape dynamics that would further reduce areas covered by natural vegetation.