| Copyright ©2003, part of The YKTA Corporation, and its licensor's. All rights reserved. |
| Home I Mind I Body I Life I Tools I New I Music Instrument I Links I Contact Us I |
| South America Desertification characteristics. |
SOUTH AMERICA
Overgrazing, cultivation of unsuitable land, land degradation by woodcutting--and
the associated water erosion--are long-standing problems in the arid regions of
South America. Wind erosion is a major threat in the semiarid pampas in
Argentina, where moving sand dunes have ruined much land. Salinity and
waterlogging have adversely affected irrigated regions in western Argentina,
particularly along the Rio Salado, and in the numerous narrow irrigated valleys
crossing the coastal plain of Peru. The very large salinas and salarea (salt lakes)
found in western Argentina, northern Chile, and the altiplano of Bolivia and Chile
are of natural origin rather than being due to man's activities. There is little
evidence of land improvement, and conditions are either worsening, or at least
not improving, nearly everywhere.
Desertification Characteristics
Heavy woodcutting for mine timbers and fuel accompanied the settling of
western South America by the Spaniards in the 16th and 17th centuries. Along
with that went localized overgrazing of livestock and the cultivation of the nearby
slopes, with the inevitable accelerated erosion, It was not until the 19th and 20th
centuries, however, that land degradation on the slopes of the Andes Mountains
and the coastal ranges become widespread. Population increases and land
tenure systems in effect in most countries of South America have combined to
put further pressure on the arid regions in recent years (Figure 6).
Desertification has been held to a moderate level in semiarid northeastern Brazil
by the erratic character of the rainfall there. Land destruction probably would
have been much worse if the rainfall were more reliable and if severe droughts
did not occur so frequently. The original caatinga vegetation is xerophytic and is
adapted to the long dry periods that occur each year (Banco do Nordeste do
Brasil, 1964).
The coast of Peru is crossed by a large number of short rivers flowing from the
Andes to the Pacific Ocean. Many of the irrigated valleys are affected to some
degree by salinization and waterlogging. The valleys constitute only a small part
of the coast desert of Peru and even less of the Chilean desert. Most of the
desert has experienced little development or desertification.
Farther south, in the semiarid coastal mountains of Chile, land degradation due
to overgrazing and cultivation of sloping lands has been severe around
population centers. Indiscriminate woodcutting has also been an important
negative factor in the development of the region.
In Argentina, which has more arid land than any other South American country,
overgrazing has led to the degradation of range vegetation from the high
plateaus in the north to the cold Patagonian desert in the south. Wind erosion
plagues both range and cultivated lands, especially in the southern half of the
nation.
Magnitude of Desertification
Overgrazing of rangelands has been the most destructive aspect of
desertification in all the arid regions of South America. There has been a
progressive elimination of palatable species by cattle, sheep, and goats over
many decades. Along with this has gone the cutting of trees for timber, firewood,
and charcoal. In the Gran Chaco of Argentina it is difficult to find good stands of
the valuable red and white quebracho trees that once grew everywhere.
Water erosion has followed overgrazing through the continent, and wind erosion
has become an acute problem in parts of Argentina (Prego et al., 1971). The
most serious wind damage has been done in the dry-farmed areas of central
Argentina where cultivation has led to the formation of mobile dunes. In 1963 an
estimated 16,000,000 hectares of land were affected to varying degrees by
wind erosion, and the situation has become worse since then. Soil fertility has
declined and runoff has increased.
Salinization and waterlogging affect about 20 percent of the irrigated land in the
coastal valley of Peru (Comite Peruano de Zonas Aridas, 1963) and large
sections of the semiarid Gran Chaco, in and around the province of Santiago del
Estero. The same problem, to a lesser degree, appears in the irrigated regions
in arid western Argentina and in northeastern Brazil.
Although only about 22 percent of the arid regions of South America are
severely or very severely affected by desertification the problem is critical
because the best lands have been degraded and the degradation is continuing.
Virtually no improvement of grazing lands has occurred anywhere, nor have soil
salinization and water-logging been controlled. Some progress has been made
in stabilizing sand dunes in the dry farming areas of Argentina but much remains
to be done. Water erosion in the Andes and the semiarid western coastal
ranges continues to present problems and may be getting worse. A fast-growing
population virtually assures greater desertification in the years ahead unless
governments become determined to cope with the problem.