Download The main consequence of land degradation is the loss of soil

Santibañez Q.F. y P. Santibáñez V. 2007 Trends in Land Degradation in Latin America and the Caribbean, the role
of climate change EN: Climate and Land Degradation World Meteorological Organization. Ginebra. Springer
Verlag p 65-81
Trends in Land Degradation in Latin America and the Caribbean, the
role of climate change.
Fernando Santibáñez and Paula Santibáñez
Centre on Agriculture and Environment (AGRIMED)
University of Chile
[email protected], www.agrimed.cl
Latin America was under populated until the XVIII century. It was located far
from the most populated centres of the world, like China, Africa and Europe where the
first human concentrations emerged. This continent was characterized for civilizations
demographically dispersed in the territory, living in a relative harmony with their natural
resources. Demographic expansion started very slowly, only 500 year ago, after the
arrival of European to colonize this land. For that reason this continent still conserve the
most part of its original genetic resources and biomes.
Latin America has probably the richest reserve of genetic resources of the world.
This region provides habitat for about 40% of the known living species, has an important
reserve of cultivated land and fresh water. About one third of the forest of the world lives
in their important tropical and temperate biomes. Some areas of the Amazonian mass and
of temperate sub Antarctic forest are among the less disturbed ecosystems that are still at
pristine condition. Otherwise, Antarctic waters are well known for their rich marine
biodiversity. Despite its genetic richness, important deforestation has affected mainly
coastal ecosystems. Originally, this continent had 6.93 millions square Kilometres of
forests. At present it has been reduced to 3.66 millions. Present rate of forest loss is
15.000 square Kilometres per year that is to say, almost 3 hectares per minute.
Soils
The agricultural potential of the region is estimated at 576 million hectares (UNEP
GEO 2003). About 24% of the Americas are arid or semiarid (Sivakumar, 2007). The
major cause of land degradation is the use of unsound cultivation practices. In South
America, about 45 per cent of croplands are affected by land degradation. In MesoAmerica these figures are mare dramatic rising up to 74 per cent of cropland.
The main source of deforestation in the Amazon is the expansion of croplands into
previously forested areas. After some years, the soil degrades and crops are abandoned to
give way to permanent pastures. Soybean production has been the main cause for the
expansion of agricultural frontier in northern Argentina, eastern Paraguay and central
Brazil.
The arid lands are threatened by desertification and very often by droughts. Both
phenomenons have high social costs pushing millions of people to move to cities, creating social
pressure in urban areas. This is one of the sources of crime increase and political instability in
many countries.
Irrigated lands are about 15 millions hectares, the most part of them show
symptoms of soil degradation. Nearly 20% of physical surface is already degraded
Biodiversity
The region contains 40 per cent of the plant and animal species of the planet. The
biota of all countries is threatened. Only Brazil has 103 bird species threatened. Peru and
Colombia occupy the fifth place in the world with 64 species each. A third of Chilean
vertebrates are threatened. Brazil also has 71 threatened mammal species (the fourth highest
in the world). More than 50 per cent of Argentinean mammals and birds are also threatened.
Highlands of Bolivia, as higher as 3800 m in the border of Titicaca Lake, support
intensive cultivation of annual crops (potatoes, quinoa). Risers of Lamas and Alpacas very
often keep a stocking rate higher than carrying capacity of degraded grasslands,
intensifying vegetation regression and soil degradation. The main processes of soil
degradation in Highlands and mountain areas are water and wind erosion. The intensive
extraction of water from wetlands is pushing them to desiccation, affecting the integrity of
rich, biodiverse and unique ecosystems, having more than 70% of endemic species.
The Valdivian Forest in Chile (dominated by Nothophagus spp) is one of the last
extensive temperate rainforests of Southern Hemisphere. After a century of wood
extraction, only 18% of the original Alerc forest survives. This is the second longevous
species in the world (trees aged of more than 2500 years). At present it is very likely that
this unique species is under her critical territory and forest structure to guarantee her
conservation.
At present, the rainy tropical forest continues to be cleared, mainly using fire, to
open lands for annual crops and pastures. Just in one year (2000), more than 12,260 km2
of rainforests were cut in the Amazon basin. In the South Eastern coast of Brazil, the
Mata Atlantica vegetation, considered a rich genetic reserve, has been reduced to small
patches.
South America's share of total tropical deforestation is 610,730 km2 /decade, while
Central America and Mexico's share is 111,200 km2/ decade. These figures indicate a total
rate of tropical deforestation higher whatever occurs elsewhere in the world.
Water
Latin American continent has big river basins with abundant water resources: the
Amazon, Orinoco, São Francisco, Paraná, Paraguay and Magdalena rivers represent more
than 30 per cent of continental runoff. Nevertheless, two-thirds of its territory is arid or
semi-arid. These areas are located in central and northern Mexico, northeastern Brazil, West
and South of Argentina, Northern Chile, Bolivia and South Western Peru. Normally arid
and semiarid parts have high agricultural potential if irrigated. An area of 697 000 km2 is
currently irrigated, corresponding to 3.4 per cent of the Latin American territory. Irrigated
areas are affected by salinization and waterlogging due to bad management of irrigation
systems.
Human drivers and ecosystems
Human drivers are normally called pressures upon natural resources. The main
source of human pressure on soil comes from unsound agricultural practices and
interventions on natural ecosystems to extract goods and services. As consequence of these
human interventions the natural equilibriums are altered triggering the chain of degrading
processes (Sivakumar, 2007). Food, raw materials and energy production, as well as mining
and industrial activity, urbanization, tourism and other human activities, exert direct or
indirect pressures on natural resources. All these human actions cause loss of mass, energy
or information contained in natural systems, often taking them to irreversible simplification
levels. Human actions on natural systems, tends to accelerate processes leading to dissipate
energy, reducing its stock of internal energy and its stability or complexity (Mosekilde et al,
1991).
Natural systems have the capability to absorb small temporary imbalances or
pressures, restoring by themselves, i.e., recovering their structural and functional integrity.
This resilience allows the ecosystems to stay unaffected through lingering periods of time
despite changes of their environment (Schnoor J, 1996). Furthermore, natural systems have
become stronger due to the slow and subtle climate changes occurred through the ages
When the imbalances go beyond the system resilience capacity, transformations
become permanent, state from which the system will not recover by itself. In such case the
system has lost information or essential components, unrecoverable in human scales of
time. Practically any component of a natural system can be modeled according to the
outline in figure 1, i.e., as a balance among the forces that it push to its degradation and
those that moves to its recovery. The important thing is to know which is the role of
population in the input and output of matter, energy and information to and from the natural
systems.
Less resilience capacity of natural systems implies higher vulnerability. In general,
the most complex systems or those that must complete longer cycles tend to be more
vulnerable, as is the case of temperate forest and wetlands. In many cases the reproduction
of the plant species and animals depend on delicate balances that, when suffering
distortions, can impede the spawning of new generations that could guarantee the stability
of an ecosystem. The simple removal of a plant species can put in risk the subsistence of an
animal species that bases its subsistence on it, in turn, this can also puts in risk the survival
of predators, triggering a series of processes whose end result is difficult to foresee.
The pressures exerted by humans are not easily describable by a single parameter.
Many times they are the result of multiple derived factors of human actions over the
environment. Additionally, an action can have effects on different environmental
components simultaneously, exercising multiple pressures over several natural resources.
This is the case of the agriculture, activity for which the natural ecosystem balances must be
radically modified exerting overwhelming pressures over plant and animal biodiversity, soil
and water resource, all at once.
Desertification
Basically, desertification is the simplification and loss of the natural balances of the
ecosystems characteristic of climates with water deficit, affecting the life quality of the
inhabitants. The arid climates ecosystems have, in general, high levels of resilience.
Nevertheless, they are considered fragile due to the high levels of water stress that affects
the vegetation communities and the poor soil protection as a consequence of the reduction
of plant cover.
One of the most relevant human interventions that triggers or worsens the
desertification process is the extraction of plant biomass, used as forage or fuel purposes.
This reduces plant cover coverage, partially increasing soil vulnerability to the eroding
action of climatic elements. Soil erosion reduces its fertility and its water holding capacity
which, in turn, triggers a chain of processes that, through positive feedback, increases the
ecosystem deterioration. Figure 1 shows a causality diagram of this chain of processes.
Vegetation removal
Anual
Rainfall
(+)
(-)
Plant cover
(-)
(-)
overgrazing
(-)
Carrying
capacity
Rainfall
exposure
(+)
Fertility and
water hoding
capacity
(+)
Soil
Cultivation
(-)
Soil
Erosion
Figure 1. Diagram of causality representing the main processes leading to soil degradation.
Climatic variability and precipitation intensity exacerbate the negative impacts of this vicious
circle.
All the processes that lead to desertification are gradual and continuous. Although
degradation of the environmental components happens, in general, with some simultaneity,
under determined managing conditions and depending on the nature of each ecosystem, it is
possible that some components degrade faster than others do. This makes each degradation
situation different from others not being possible to generalize a single route toward
desertification. Nevertheless, it is necessary to have a numeric language that allows the
representation and comparison of the various degradation profiles of the different
ecosystems that compose a territorial system.
Present trends of Climate
Land degradation is a consequence of a combination of human and climatic
drivers. Climate has been fluctuating forcing important landscape changes in the last
thousand of years (Climatic trends are evident in extensive areas of the continent
(Telegeinski-Ferraz et al, 2006). Temperature records in tropical Andes show a significant
warming of about 0.33°C per decade since the mid-1970s. Minimum temperature in
Chiclayo, Peru’s north coast, increased 2°C from the 1960s to 2000. Similar trends were
observed in Chile (Rosemblüth B, 1997). The trend has been observed in the high plateau
region in extreme southeastern Peru were minimum temperature has risen 2°C from 1960
to 2001. (http://www.climatehotmap.org/samerica.html). In the 20th century, temperature
changed faster than in the precedent centuries, showing a clear acceleration in recent
decades (Villalba et al, 2003)(Figure 2). Daily time series have shown no consistent
changes in the maximum temperature while significant trends were found in minimum
temperature, in Western and Eastern coastal regions of South America (Vincent et al,
2005). In the South Western Pacific coast, rainfall has shown a clear negative trend
throughout the 20Th century. A contrary trend has been observed in the Atlantic coast of
Argentina and Southern Brazil, like in many other parts of the world (IPCC, 2007). Mean
annual precipitation in the humid Pampa increased by 35% in the last half of the 20th
century (Figure 3).
Figure 2. Surface temperature change in Brazil and Argentina over the last century
(Source: Grid Arendal : http://maps.grida.no/go/region).
Climatic variability seems to be increasing, making more frequent extreme
climatic events of drought and floods (Aguilar et al, 2005). In the Amazonian basin water
regime tend to move to a more arid condition due to deforestation which is reducing vapor
transfer to the atmosphere (Durieux et al, 2003). Amazonian rain forest is one of the few
examples of clear interaction among forest cover and mesoclimatic regime.
In the overall continent a rapid reduction in the permanent ice bodies is observed,
mainly Andean permafrost and glaciers, which moved upward their lower front about 300
meters or more in a century (Figure 4). Some glaciers from the Southern Argentina and
Chile have retrieved hundred of meters and reduced its thickness at a rate of 100
centimeters per year. Glaciers in Patagonia have receded by an average of almost a mile
(1.5 km) over the last 13 years. In 1972 Venezuelan Andes had 6 glaciers, at present only
2 remain, and it is expected that these will be gone within the next 10 years. All this
trends are affecting the global hydrology of the Andean basins and water availability for
irrigation of important agricultural areas in Chile, Argentina and Peru.
Buenos Aires (Argentina)
Relative precipitation
1,50
1,40
1,30
1,20
1,10
1,00
0,90
0,80
0,70
1840
1860
1880
1900
1920
1940
1960
1980
2000
year
Relative precipitation
La Serena (Chile)
2,00
1,50
1,00
0,50
0,00
1860
1880
1900
1920
1940
1960
1980
2000
year
Figure 3. Running average (10 year period) of annual rainfall in Buenos Aires
(Argentina) and La Serena (Chile)
Figure 4. Retreat of Ice cap on Volcano Nevado Santa Isabel (Colombia).
(Source: Grid Arendal : http://maps.grida.no/go/region).
Ecosystems
Ecosystem vulnerability depends on climatic agressivity and variability, soil type,
vegetation resilience and landforms. Social vulnerability depends on ecosystem
vulnerability, economic resources, access to technology and social structures and
assistance networks.
Highlands of the Andean region are very sensitive to climatic variations due to the
presence of populated human settlements, the complex landforms and a dynamic
hydrological system. Land slides and avalanches are a permanent threat for small villages
and agricultural lands.
In Mediterranean climates, having a long dry spring and summer, precipitations
concentrates in a short rainy period of 3 to 4 month. When the first precipitations arrive, a
dry bare soil is intensively eroded provoking massive sedimentation of rivers and lower
lands. This phenomenon was exacerbated in the last century as a consequence of soil
denudation, where dense chaparral and savannas were replaced by degraded annual herbs
unable to protect soil from water and wind erosion. In some areas close to the cities, the
Andean piedmont has been urbanized provoking a rapid run off and flooding during
intensive precipitations.
Main biomes of the continent are submits to different natural and human drivers or
pressure. Pressure having a human origin depends on population density and productive
use of natural resources. Natural pressure depend basically on climate change, that is
forcing ecosystem to adapt to new environmental conditions and creating more adverse
conditions for soil conservation. Normally human and natural drivers interact negatively
making difficult to sustain the integrity of ecosystems. Another component of land
degradation is ecosystem vulnerability, which can be defined as the property of natural
vegetation, animal species and physical environment as a functional unity, to resist,
absorb or to neutralize an external perturbation without having permanent modifications.
Different biomes have different vulnerabilities depending on their capacity to restore their
original condition after a human intervention or a natural environmental change. The
figure 5 presents an estimation of present human and natural pressures, and estimated
sensitivity of the main biomes.
Population
pressure
H
L
Climate change
pressure
M
ES
Warm
LS
LS
Atacama
desert
LL
ES
Andean
altiplano
HH
Cold
Dry
LS
NE Catinga
Chaco
HH
HL
M
Dry Pampas
HL
ES
Patagonian
steppes
HL
Rain
Forest
HH
M
ES
ES
ES
Sclerophylus
forest
HH
Temperate
forest
HH
sub antarctic
Tundra
LH
Humid
Figure 5. Relative situation of the main Latin American and Caribbean biomes,
related climate change, human drivers and sensitivity. (H=high pressure, L=low pressure,
LS=less sensitive, M=medium sensitive, ES=extreme sensitive)
Agriculture
Soil degradation is affecting productivity of agricultural lands and livelihood of
population, ecosystems as well as natural plant cover and biodiversity.
Land degradation is the result of a number of causes, as unsound agricultural
practices, ecosystem fragility, human pressure and climate which is getting more
hazardous. Land degradation is the first phase of a long chain of processes affecting the
integrity of the ecosystems, ecosystem services and the capacity of the territory to sustain
human activities. One example of this is the El Niño-La Niña phenomenon. During the El
Niño phase, Pacific water warms 2 to 4 degrees bringing intensive precipitations in the
Southern Cone (Peru, Chile, Argentina, Pacific and Atlantic coasts), while droughts affect
Colombia, Venezuela, Mexico, North Eastern Brazil and the Amazon basin. The cold
phase is associated with inverse effects. This phenomenon is a real threat for human
settlements, being the main cause of floods and landslides. Periodic droughts create
unfavourable conditions for investments in agriculture. This oceanic oscillation is
probably the main driver for climatic variability in the continent, making precipitations
highly hazardous, forcing farmers to make agriculture of low inputs in order to reduce
economic risk. This leads to a marginal agriculture, associated with low yields and
income, and consequently, social deterioration and very often, the primary cause of
massive migrations. This has been the case of North Eastern Brazil, Northern Argentina,
Northern Chile and Mexico (MA Secretariat, 2002; NRC, 2002).
Land degradation is the end result of a long chain of processes having different
beginnings (Pielke et al, 2007). The most common is social marginality and lack of
economic and technological resources (Figure 6). Under these conditions, farmers, often
small owners, tend to minimize cost using basic and aggressive techniques of soil
cultivation, leading to soil erosion. A second cause has historically been mining. High
energy requirements of metal foundry, stimulated deforestation of fragile ecosystems to
provide mines with fuel wood and charcoal. The third cause was industrial agriculture that
used high levels of fertilizers, pesticides and machinery. This combination leaded to the
loss of organic matter, soil compaction and, after some years, a global decay in soil
productivity. In all cases there was a combination of human pressure and climate
aggressivity threatening important ecosystems. In tropical areas, sugar cane cultivation
during the last three centuries and especially in the late 18th century, was the primary
cause for forest cover removal to install unsustainable production systems. Much of this
land had only shallow and fragile soils highly erosion prone due to the steepness of the
slopes it occupied. Consequently it was observed a loss of significant amounts of topsoil
from many areas, especially in the volcanic soils of Meso America. Although the worst
affected areas are no longer in cultivation, the natural vegetation that has recolonised
these areas is much poorer in species composition and biomass than the original
vegetation
Land use / Human activities
Marginal lands
good lands
Poverty
intensive agriculture
Unsound practices
due to lack of
technology
unsound practices due to
the lack of environmental
considerations.
Plan cover removal
and forest fires
soil compaction
salination
chemical deterioration
flooding
slope cultivation
overgrazing
soil erosion
decay of soil productivity
AGRI DESERTI
afforestation
urbanization
Figure 6. Paths to land degradation. Good lands with intensive agriculture and
marginal lands with low input agriculture follow different path by the end results are
similar. The Agri Deserti is a completely degraded land unsuitable for agriculture.
In arid and semiarid parts of the continent, low and variable rainfall create a
permanent water stress that produce poor stands of sparse vegetation, which provide
ineffective protection to the soil from the erosive effects of rainfall and wind.
The effect of climatic variations on crop productivity is difficult to predict due to the
complexity of the cause effect relationships among plant ecophysiology and climate. In
some case the effect of higher temperature is clearly negative, in some others, clearly
positive. The balance of negative and positive impacts will determine the behavior of
crops in new climatic scenarios. A rise of temperature in cold climates will be certainly
positive, stimulating growth rate and biomass accumulation. If this phenomenon is
accompanied of precipitation reduction, the negative effect of this will oppose to the
positive change in temperature regime. The final result will depend on what of the two
phenomenons will predominate over the other. In tropical regions, a rise of temperatures
will create conditions for thermal stress being deleterious for crops. Simultaneously a
higher CO2 content will allow plants to better support these stressing conditions, due to
higher photosynthetic rate, which provide more carbohydrates to maintain higher
respiration rates. What is expected in all climates is the fact that global warming will
accelerate life cycles of pest and insects, increasing sanitary equilibrium of plants.
Analogously, life cycle of plants will be accelerated reducing time for biomass
accumulation. This will affect yields negatively. To neutralize this phenomenon cultivated
areas should move to fresher climates when possible or change sowing dates looking for
the lower temperatures during the year. Areas where these two possibilities are unlikely,
agricultural yields will fatally drop.
In hot tropical climates, temperature rise will force crop yield to decrease, by
shortening the duration of crop growth cycle. Phenology will occur faster reducing the
duration of phonological phases, consequently, production of fruits, grains and plant aerial
organs will drop. In arid climates of the continent (NE Brazil, Northern Mexico, Peru and
Chile, and Southern Argentina), this negative impact is reinforced by a decreasing annual
rainfall. In humid tropical climates (Amazon basin, Northern Argentina and Meso
America) the higher temperatures interact with a more aggressive and unstable
precipitation pattern in the recent decades. Along the Central American-Caribbean
watersheds, coffee and banana crops could be additionally stressed if climate change leads
to increasing frequency of storms and heavy precipitation (Campos, et al 1997).Ozone
depletion (WMO, 2003) also contribute, in the Southern part of the continent, to increase
UV levels that impair the growth of some crop species due to its deleterious effect of
auxines. One exemption is the vine, species that beneficiate from increased levels of UV,
which increase the synthesis of flavonoids improving the quality of wine.
Global warming also will create better conditions to extend the geographic
distribution of insects and pests. Higher temperature accelerates reproduction, shortening
the time to complete life cycle of insects and pathogenic agents (Porter et al., 1991).
Changes in precipitation regime can increase sensitivity of hosts, reducing predator
populations and competitors (Löpmeier, 1990; Parry et al., 1990; Parry et al 1991). There
is some evidence of poleward expansion of pest and insect distribution ranges which can
create new sanitary risk in temperate climate (Porter et al., 1991). This expansion is
expected to continue affecting highlands and temperate agriculture. An example of this
was the arrivals of late potato blight (Phytophthora infestans) in Central Chile in the early
1950 (Treharne, 1989). Figure 7 shows positive and negative effects of climatic warming.
new areas for
tropical fruits
Positive effects
Growing season
extends
Frost regime gets
milder
better conditions
for pollinization in
cold climate
temperature
rise
New pest and
diseases
Milder winters
chilling hours deficit
negative effects
reduction of temperature
amplitude deteriorate quality
for temperate crops
High temperature
stress
Shorthening life cycle
of pest and diseases
Acceletation of
phenology of crops,
less biomasse
Figure 7. Summary of positive and negative effects for crop species of temperature
rise
In extensive areas, farmers have limited financial resources and low input farming
systems having little capacity to adapt to the new condition imposed by climate change.
Adaptive capacity requires efficient irrigation and water management systems, highly
technified management of pests and diseases, an strict control of climatic risks by
managing early warning systems and information systems (GCOS, 2003), adaptation of
genetic resources (to change crop seasonality and increase resistance to pest and diseases),
highly technified management of pesticides and fertilizers (to prevent contamination of
waters and foods). In some areas farmers will never be able to adapt to these conditions at
the required speed. Marginal agricultural populations may suffer significant disruption
and financial loss even facing relatively small changes in crop yield and productivity
(Parry et al., 1988; Downing, 1992; GEF, 2006). Currently, prices of agricultural products
are at the lower limit to support reductions on yields, so, farmers are in an extremely
vulnerable condition.
Due to higher prices of energy, pesticides and fertilizers, estimated net economic
impacts of climate change on crops are negative for several Latin American countries
analyzed by Reilly et al. (1994).
Globally the continent will endure important climatic modifications all over its
territory. Changes in South America, especially in coastal areas, could be moderated by
the important mass of Oceans in the Southern Hemisphere. Despite this, important
modification is expected in the behavior of climatic oscillation as El Niño-La Niña, which
will continue to be a driver for climatic variability in almost all continental extension
(Paeth et al, 2006). Isotherms and isohyets displacements are occurring faster than
adaptation mechanisms of natural ecosystems; this could become a severe threat for
important biomes of this continent, mainly in the Amazon basin and temperate rain
forests. Modification of rainfall regimes, the retreat of ice bodies and increased rates of
evaporation, could reduce runoff and available water in the next decades. Global warming
will force important adaptation in agricultural systems, this include the better use of
technology and a shift in crop seasonality. Only modern agriculture will adapt to these
new conditions impacting severely small farmers which dominate in extensive areas of the
continent. After analyzing these trends, some questions arise: Will we halt this tendency
before a real crisis? how much will we pay to adapt to a new climate?, will we be able to
adapt completely to new planetary situations?. These questions imply a real effort to
restore the planet to his normal situation.
Main Changes forced by global warming in Latin America and the Caribbean
Glaciers and
permafrost
Soil
Freshwater
Water quality
Climatic
variability
Upward displacement of at least 300 meters of lower border
of Andean glaciers, decrease in the Antarctic Ice extent,
retreat of the Patagonia glaciers, reduction of permafrost,
reduction of solid precipitation and snow reserves in the
Andes and high elevations.
More intense storms could increase risk of soil erosion. Even
in arid environments occasional intense storm could
threaten bare soils.
Increased runoff in winter reducing availability of water in
spring and summer. Loss of capacity of hydrological
regulation of the main river basins in the Andes Mountain
based on snow reserves.
Decreasing precipitation is reducing potential for rainfed
agriculture in arid environments. As consequence of this,
groundwater is being overused, increasing depth of water
tables.
Intensive storms are more frequent, causing more soil erosion
and sediment transportation to rivers.
Higher temperatures tend to reduce dissolved oxygen
impairing aquatic organisms.
Stalinization of river deltas due to the increase in sea level.
Extreme climatic event are increasing its frequency, making
life hazardous. This is affecting wildlife and agriculture.
Some ecosystems from the Atacama Desert border are in
ecological regression due to the increased climatic
variability which magnifies human pressures.
Drought, floods and landslides are affecting agriculture
and human settlements. In some cases causing loss of
human lives.
In May 2000, the region of Buenos Aires, Argentina
Rangelands
Forests
Biodiversity
Soil Carbon reserves
and organic mater
Crop
seasonality
Human health
supported the heaviest rains in 100 years, 342 mm fell in
just 5 days. Similar phenomenon affected Venezuela in
December 1999, causing massive landslides and flooding
that killed approximately 30,000 people.
Important areas of the continent support extensive cattle
production, in some cases this activity represent un
important export product (Uruguay and Argentina). These
agricultural ecosystems are threatened by water and wind
erosion due to increased climatic aggresivity.
The continent holds one of the bigger world forest reserves.
Tropical forest is threatened by a combined action of
humans and climate. Tropical forest soils in the Amazon
basin are very sensitive. After a slight deforestation,
exposed soil start
Global warming and changes in water regime are threatening
important biodiversity of tropical rain forest (Amazon
basin and Central America), Semiarid tropical steppes
(Caatinga from the NE Brazil), Cold Steppes of the
Andean highlands (mainly Peru, Bolivia, Argentina and
Chile), Subdesertic and semiarid temperate Steppes in
Mexico, Peru, Chile and Argentina, Humid temperate
forest (evergreen and deciduous) in Chile and Argentina
and Cold Patagonian Steppes. Primary factors of
degradation of these biomes is soil desiccation and
droughts, displacement of isotherms faster than species
adaptation and frequent intense storms which degrades or
saturate soils. Temperature increase also creates favorable
conditions for new species of insects or diseases. Rising
sea level is leading to saltwater inundation of coastal
mangrove forests in Bermuda.
Higher temperatures favorise organic mater degradation when
soils are cultivated. This accelerates the loss of carbon
from cultivated soils. This is the normal situation in
tropical soils, which is shifting to temperate zones.
Higher temperatures will be compensated with changes in
crop seasonality. Sowing dates will move towards the
coldest season to maintain yields. In Mediterranean
climates this could help in a better use of winter rains,
reducing water requirements. This paradox was already
seen using simulation models in South America.
Until 90’s decade Aedes aegypti mosquitoes that can carry
dengue and yellow fever viruses populated lower lands
up to 1000 m. Recently appeared at regions above 2000 m.
Source: modified from Santibáñez (1991), IPCC (2007) and van Dam et al. (2002),
Campos, 1996
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