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

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Grasslands of the world
In Paraguay , the Chaco, referred to as the “western region”, is almost flat,
with 32 000 km 2 suitable for crops , but only a very small area is cultivated. The
grazed area covers 124 000 km 2 , mostly on natural grassland . Two main vegetation
groups are recognized in Paraguay: the xeromorphic group dominates
the landscape ; matorral is the main formation in all the centre, north and west.
Mesomorphic vegetation that dominates towards the south and centre-east
develops on heavier, better structured soils and is covered by a mosaic of alternating
forest of Schinopsis balinese, Caesalpinia paraguariensis and Phyllostylon
rhamnoides; palm-savannahs of Copernica alba ; and marshes.
Extensive livestock rearing is, and will probably remain, a major land use
in the Chaco. Bush encroachment brought about by overstocking and lack of
grazing management is very serious, leading to erosion, loss of wildlife habitat ,
and greatly reduced livestock production. The economics of herbicides and
mechanical clearing are not clear. In most sub-tropical areas of extensive grazing,
the strategic use of pasture resting and controlled fire is the only economic
way of keeping bush in check.
Poor management in the Chaco leads to invasion by unpalatable weeds,
caused by loss of soil fertility, which must be kept at high levels to assure
survival of introduced forages. Proper adjustment of carrying capacity is also
essential. Natural grassland is better than degraded, weed-infested, “improved
pasture ”. Sown pastures may have an important role in the Paraguayan
Chaco compared with the rest of the area.
Pampas
The Pampas (Garbulsky and Deregibus, 2004), which occupies about 50
million hectares between the 2°C and the 13°C isotherms, has a temperate
climate with mild, snow-free winters. Precipitation decreases from 1 200 mm
in the northeast to 500 mm/yr in the ecotonal change to the Monte region.
Rain is evenly distributed through the year in the east, but is concentrated in
the warm season in the west.
This Region is characterized by its lack of native trees, flat terrain, fertile soils,
extended croplands and native or sown pastures. As soils are fertile and summers
shorter and milder than in the north, many C3 grasses and temperate legumes
grow during the cool season. Thus a seasonal alternation occurs between
C4 and C3 plants. Species alternation maintains green grass year-long and is ideal
for resource utilization in a seasonally variable climatic environment; mild water
deficits in summer are better overcome by C4 grasses. Temperate grasses and
legumes of good quality (above 20 percent protein and 70–80 percent digestibility)
allow total utilization during winter of the remnant biomass of summer
grasses, so there is seldom accumulation of forage in winter.
Native humid-grasslands cover the Flooding Pampa, some parts of Entre
Ríos Province and most river and stream banks. Their warm season components
are grasses of the Panicoideae, Chlorideae, Andropogoneae and