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T
HE LOSS OF
biodiversity and a significant deterioration
of soil productivity have resulted from a number of
causes such as agricultural practices, ecosystem
fragility, human pressure and climate aggressivity. In tropi-
cal areas, sugar cane cultivation during the last three
centuries, and especially in the late 18th century, was the
primary cause of forest cover removal as unsustainable
production systems were installed. Much of this land had
only shallow and fragile soils, which were highly prone to
erosion due to the steepness of the slopes. Consequently it
the loss of significant amounts of topsoil was observed in
many areas, especially in the volcanic soils of Meso America.
Although the worst affected areas are no longer in cultiva-
tion, the natural vegetation that has recolonised these areas
is much poorer in species composition and accumulated
biomass than the original vegetation
In arid and semiarid parts of the continent, low rainfall and
frequent periods of drought stress generally produce poor
stands of sparse vegetation, which provide ineffective protec-
tion to the soil from the erosive effects of rainfall. The same
low rainfall reduces the rates of weathering that lead to soil
formation, thus tilting the balance towards a shallower soil.
Argentina has significant soil erosion in La Rioja, San Luis
and La Pampa provinces. Overgrazing has been severe,
causing erosion and river sedimentation. In the west, salin-
ization due to unsound irrigation practices has become a
serious problem.
The semiarid North East of Brazil supported cotton plan-
tations for centuries, moving to sugar cane in the last decades.
The small size of exploitations, poverty and high climatic
variability make this extensive area highly vulnerable.
Periodic droughts and land degradation provoked massive
migrations to the south and the Amazonian states.
1
The Andean region from Venezuela to the Patagonia is very
sensitive to climatic extremes due to the presence of popu-
lated human settlements in the highlands, and to its complex
topography and hydrology. Land slides and avalanches are a
permanent threat. In some areas of the Chilean Andes, having
a Mediterranean climate with a long dry spring and summer,
the first precipitations in winter fall over a dry, bare soil,
provoking erosion and massive sedimentation transported by
the rivers to the lower land of the Central Valley. This
phenomenon was exacerbated in the last century as a conse-
quence of the change of natural shrub cover by degraded
annual herbs. In some areas close to the cities, the Andean
piedmont has been urbanized, provoking a rapid runoff and
flooding during intensive precipitations.
Populated highlands of Bolivia, as high as 3,800 metres at
the border of Titicaca Lake, support intensive agriculture
(potatoes, quinoa). In addition, these highlands support
grazing pressure from Llamas and Alpacas. Soils are moder-
ately to intensely degraded by water and Aeolian erosion. The
intensive extraction of water from the small watershed is
pushing rich and biodiverse wetlands to desiccation.
The Valdivian Forest in Chile is one of the last two exten-
sive temperate rainforests on Earth. After a century of logging,
under 2,600 km
2
of Alerc forest remains (in the rugged, rainy
coastal mountains south of Puerto Montt). Today, 18 per cent
of the original Alerc forest survives; this is the second oldest
forest in the world (trees aged more than 2,500 years).
The tropical rain forest continues to be cleared to open land
for pastures. Fire continues to be used for this purpose. In
2000, more than 12,260 km
2
of rainforest were cut down in
the Amazon. On the southwestern coast of Brazil, the Mata
Atlantica vegetation has been reduced to small patches.
In Central America about 36 per cent of tropical forest
losses seem to be attributable to grazing. Tropical South
America’s share of total tropical deforestation is 610,730 km
2
per decade, while Central America and Mexico’s share is
111,200 km
2
per decade. These figures indicate a total rate of
tropical deforestation via grazing of 480,000 km
2
per decade
plus whatever occurs elsewhere in the world. The original
forests of Latin America covered 6.93 million km
2
. The esti-
mate for 2000 is 3.66 million km
2
.
The human drivers of land degradation interact in this
continent with climatic trends everywhere. On the South
Pacific coast of Chile, rainfall showed a clear negative trend
throughout the 20th century. At the same time this trend was
positive in the Atlantic coast of Argentina and southern Brazil,
as in many other parts of the world.
2
There is evidence of
increased climatic variability in northeastern Brazil and nega-
tive trends in water regimes of the Amazonian basin. Mean
temperature has increased about 0.6 degrees in the last
century, provoking a rapid reduction in the Andean
permafrost and glaciers, the lower edges of which have moved
up by 300 metres or more in a century. Some glaciers from
Southern Argentina and Chile have retreated hundreds of
metres and reduced their thickness at a rate of 100 centime-
tres per year. All these trends are affecting global hydrology
and water availability for irrigation.
Global warming, climatic trends and climatic
threats in Latin America and the Caribbean
Fernando Santibañez and Paula Santibañez,
Centre on Agriculture and Environment (AGRIMED) University of Chile