Grasslands of the World.pdf - Disasters and Conflicts - UNEP

428
Plate 11.8
Park grasslands in NE Chaco, a summer view.
Grasslands of the world
It slopes gradually eastwards, at 100–500 m above sea level, except for the
Sierras in Cordoba, Argentina , which reach 2 800 m. The climate, of the wetdry
season al type , varies without sudden changes since there are no natural
barriers. Temperatures rise from south to north and rainfall from west to east.
The warmest months coincide with those of maximum rainfall, which favoured
the evolution of herbaceous forages of the C4 type.
Most early settlement was along the coast and major waterways. A railway
and water supplies opened the Chaco to settlement. Commercial beef production
developed in the nineteenth century. Large tracts were colonized and the
exploitation of the Chaco began in earnest. Between 1910 and 1920, the southeast
of the Paraguayan Chaco was an area for extensive cattle production and
sugar cane growing. Grazing was totally unmanaged, there was uncontrolled
burning , and overfelling of forest led to its replacement by undesirable thorny
vegetation .
Introduction of livestock alone is not enough to explain the dramatic and
rapid changes that took place in the vegetation . The most potent factor was the
dispersion of watering points so that a much greater proportion of the herbage
could be consumed, leaving little or none to be burnt. The demise of the
fire climax led to an increased scarcity of forage through increased grazing and
increased growth of unpalatable, woody species. This was the only grassland
intervention introduced by the ranchers. Grazing was continuous , with mixed
herds of cattle , horses, goats , asses and sheep roaming uncontrolled on the
same land, with no limits but the distance to water in the dry season ; small
V. ALEJANDRO DEREGIBUS AND MARTIN F. GARBULSKY