Ecological interactions, feedbacks, thresholds and collapses in the Argentine Pampas in response to climate and farming during the last century

The Western Pampas consists of a large and complex sand dune system that originated during the last Pleistocene glaciations and was reworked during later semi-desertic episodes. Humans only colonized the region during the last century, but their action was powerful enough to produce two catastrophic events: one during the first half of the century, and the other one during the second half. Deforestation, over grazing, over cropping plus a non-suitable tillage technology in interaction with extremely dry and windy conditions of the 1930s and 1940s, caused a large dust-bowl episode that triggered severe dust storms, cattle mortality, crop failure, farmer bankruptcy and rural migration. During the second half of the century, improved rainfall conditions favored the conversion of abandoned lands into grazing lands and croplands. At the same time, recurrent episodes of flooding affected the area between 1970 and 2002, more drastically in the highly productive lowlands of the Rio Quinto Watershed. The configuration of dunes with respect to the slope, and the lack of a suitable infrastructure, impeded water removal and favored its accumulation. High cultivation rates dramatically increased the severity of floods during such humid periods. The ecological catastrophes of the Western Pampas during the 20th century were the result of a complex interaction involving the geological configuration, climate variability and human intervention. Over cropping has probably surpassed critical ecological thresholds and this, in turn, triggered both the dust-bowl and the flooding events. On the other hand, natural feed-back mechanisms were probably activated allowing a later stabilization and recovery of the affected lands. (c) 2006 Elsevier Ltd and INQUA. All rights reserved.