Humans Cause Deserts: Evidence of Irreversible Changes in Argentinian Patagonia Rangelands

Argentinian Patagonia is a 750,000 km2 semi-arid region. Sheep were introduced there in the late 19th century, peaked at about 20 million head in 1960 and fell sharply thereafter reaching 8 million at present. Decline in productive capacity was blamed on overgrazing or climate change alternatively, but maps in 1998 indicated that 34 % of the region was severely desertified. We analysed the regional FPAR in the GIMMS NDVI dataset from NOAA satellite imagery in the last 30 years, a period in which the land has been destocked and under generally improved management. The trend of FPAR does not show a generalized “greening”, or recovery process, even when the rainfall trend was removed. A case study in Los Pozos Farm in the south shows that total stock has fallen monotonically since 1930 under a rainfall regime that remained constant. Variable stocking rates that tracked the productivity introduced in 1990 stabilized grazing capacity but did not induce a clear recovery in forage production. The erosion of unstable soils and damage to perennial vegetation probably explain the farm production losses, and management rather than climate change is the most probable cause. Production analysis shows that stocking rates that maximize short-term income in wool are too high and will probably damage the land. Good management has the potential to stabilize and maybe slowly revert long-term mismanagement effects on these cold desert ecosystems, but under the present market economy and land tenure system it seems unlikely that producers will give up profits to avoid possible long-term degradation.