According to the report on freshwater resources at
Earth
Summit 5 (1997 in New York):
"The world faces a worsening series of regional and local
water crises. Overuse and pollution are limiting the amount of
freshwater that is available to safely meet the needs of human society
and of the ecosystem, according to the
Comprehensive Assessment of the Freshwater
Resources of the World, prepared for the United Nations
Commission on Sustainable Development and presented to the June 1997
General Assembly Earth Summit Review. With agriculture highly dependent
on access to ample freshwater resources for irrigation in addition to
rainfall, qualitatively improved irrigation techniques will be necessary
if there is to be enough food for the world's growing population, the
study finds.
Other conclusions from the UN's 1997 Assessment:
Freshwater is a fundamental resource for development,
used in agriculture, industry and households. It is a resource for which
there is no substitute, whether as drinking water for people and
animals, for hygiene, for crops and industrial processes or for fish and
aquatic life.
But the volume of current consumption can be reduced
without necessarily detracting from standards of living or curtailing
economic growth, and the technologies to make this possible are already
available. It is largely a question of successfully adapting human
activities to the exigencies of water supply. The Assessment points out
that the amount of water used for intensive crop irrigation in dry areas
can be reduced by purchasing food on the world market. Industrial
processes can be modified to use less water, and household use -- which
in any event is a small portion of overall water consumption -- can be
reduced in developed countries without detracting from the quality of
life. Especially in arid or semi-arid regions, low-value water-intensive
economic activity needs to be progressively replaced by high-value
enterprises that use smaller volumes of water.
Much of the needed improvements would be facilitated by a
graduated elimination of water subsidies and by the introduction of
pricing policies that take into account the costs of delivering and
cleaning water for re-use as well as the needs of the poor.
Freshwater availability
The Earth is the "blue planet", with three fourths of its
surface covered by water. But 97.5 per cent of that is salt water. Only
2.5 per cent is fresh, and nearly 70 per cent of the freshwater is
locked in the ice sheets of Antarctica and Greenland. Much of the
remainder resides in deep underground aquifers.
Freshwater comes from the water which evaporates from the
ocean, at a rate of more than half a million cubic kilometers a year.
Nearly 90% of this evaporated water falls back into the sea as rain. And
most of the rainfall that reaches land is evaporated before it is
available for human use. The 47,000 cubic kilometers that returns to the
oceans via rivers, groundwater and glaciers -- known as the global
runoff -- is the amount that is theoretically available for human use.
There
are further limitations on the volume of freshwater useful to people.
Among these are geographical and temporal variations in precipitation --
too little rainfall in desiccated areas or during dry seasons, and too
much in humid areas or during wet seasons. All in all, about 14,000
cubic kilometers is estimated to be easily available for human use. Even
though this is still an impressive amount of water -- weighing in at 14
trillion metric tonnes -- the Assessment finds that the capacity of the
hydrological cycle to supply water is being outstripped by the volume of
human demands, pollution of water resources and poor water management.
Moreover, freshwater is unevenly distributed over the planet, and large
water diversion projects are often associated with problems in the areas
where the water is used as well as in the source area. The U.N. study
finds that many major rivers -- such as the Colorado in the United
States and rivers flowing in the Aral Sea -- are decreasing in volume as
they flow downstream, and that use of groundwater resources is
outstripping the rate of natural recharge.
How water is used
Irrigation of crops accounts for nearly 90 per cent of
total human consumption of freshwater resources. Although most crops are
rain-fed, irrigated farmland generally is more productive --
contributing almost 40 per cent of total food production on only 17 per
cent of cultivated land. The problem is that irrigation siphons off
large volumes of freshwater from waterways and groundwater aquifers.
Diminished river flows hurt aquatic ecosystems, and depletion of
aquifers leads to lower groundwater tables, which in coastal areas may
become infused with saltwater.
The hydrological cycle is the governor of freshwater, to
which humans and ecosystems have to adapt. Human activity interacts at
all stages in the cycle. We use freshwater from lakes, rivers and
groundwater aquifers; we pollute the same water and, through air
pollution, the water in the atmosphere. Changes in landscape due to
agriculture, forestry and urbanization bring about changes in water
run-off and the ground's storage capacity. Thus, there is a close link
between land and water management. (From the Comprehensive Assessment of
the Freshwater Resources of the World, after an original from the World
Meteorological Organization.)
Outside of irrigation, the largest segment of human water
consumption is devoted to industrial activities. The problem in terms of
freshwater resources generally has less to do with the quantity of water
used than with quality, i.e., wastewater which contaminates rivers,
lakes and groundwater.
Although personal and urban consumption accounts for only
a small fraction of total water use, sewage from these sources causes
major health and ecological problems in all regions, and particularly in
developing countries. In most cities in developing countries, only about
10 to 20 per cent of wastewater is treated. According to a projection --
prepared for the Food Summit in Rome -- that assesses trends in
agricultural, industrial, municipal and household water use, global
freshwater requirements for the year 2025 will exceed by 5% the 14,000
cubic kilometers of water that is accessible without tapping deep
underground aquifers. If freshwater demand is not to exceed supply
sometime during the next quarter of a century, improvements in
conservation as well as in capacity to clean and re-use water need to be
implemented.
Policy Issues
Stresses on water and land are closely linked, the
Assessment shows. Soil and water mismanagement intensifies erosion,
denuding the earth of topsoil and nutrients and polluting watersheds
with organic particles and silt. Eroded material may be deposited in
lakes and reservoirs, gradually reducing their water storage capacity.
Irrigation of arid areas where there are inadequate
drainage systems produces waterlogging and soil salinization. About 20
per cent of the world's 250 million hectares of irrigated land is
salt-affected to such an extent as to reduce crop production, and an
additional 1.5 million hectares are affected each year. The countries
most severely affected are located predominantly in arid and semi-arid
regions. Another threat caused by modern agricultural practices is the
use of pesticides and chemical fertilizers, which leach into the soil,
work their way into the groundwater and eventually degrade coastal
areas.
Increased food production to combat malnutrition among
about 800 million people and to feed a growing world population must
essentially come from intensification of agriculture, rather than
expansion of cultivated land, according to an analysis prepared for the
Food Summit. The intensification potential of irrigated agriculture is
much higher than that of rain-fed agriculture, but so are the
environmental costs. Cutting-edge techniques for more efficient
irrigation need to be utilized to save water and reduce negative
environmental impacts. Such techniques generally require a high initial
investment, according to the Assessment. But practices such as drip
irrigation can reduce water use by 25 to 90 per cent while increasing
crop yields by 50 to 100 per cent.
Even if agricultural production is intensified, it is
expected that new areas of land will have to be brought under
cultivation to meet rising food demands. According to a report of the
Food and Agriculture Organization of the United Nations, 90 million
hectares of land will need to be brought into cultivation by 2010, and
half is likely to come from forest areas that presently conserve
rainwater and protect soil from erosion.
A longstanding goal of the international community is the
provision of drinking water and sanitation for all. But despite access
to sanitation provided to an additional 200,000 people each day during
the UN's International Drinking Water Supply and Sanitation Decade
(1981-1990), gains were outstripped by population growth. The problem of
inadequate water supply and sanitation needs to be addressed with
demographic, economic and social aspects taken into account. Enabling
access for all to safe drinking water and sanitation by 2025 means
meeting the needs of an additional 5 billion people, or about 450,000
each day.
High-intensity use in urban and industrial areas may
place severe stress on freshwater resources in surrounding localities.
The Assessment reports an estimated household consumption in industrial
countries of 150 to 200 litres of water per day, with an additional 150
to 200 litres per person per day going for various municipal services.
Additional conservation measures could reduce the per capita amount of
usage. But in the developing countries, it can be anticipated that
current per capita usage, which is about 50 litres/person/day in many
urban areas, is sure to increase in the coming years. This will
necessitate additional water-treatment capacity and improved
water-management capacity.
Problems related to freshwater impact most severely on
low-income countries, in which three-quarters of the population must
survive with a per capita income of less than $2,895. Thirty-four per
cent of the population in the developing world live in countries
currently under moderate to severe water stress ("moderate stress" is
defined in the Assessment as human consumption of more than 20 per cent
of all accessible renewable freshwater resources; "severe stress"
denotes consumption greater than 40 per cent). The Assessment projects
that as many as two thirds of the countries in the lower-income
categories could face moderate to severe water stress by the year 2025.
Other low-income countries that are not under stress in
terms of consumption as a percentage of available resources nevertheless
face crises due to pollution and to a lack of institutional and
technological capacity to utilize water resources within their
boundaries or adjacent to them.
The proportion of people in the industrialized world who
live in countries facing moderate to severe stress -- 31 per cent -- is
nearly as high as in poor countries, although the richer countries have
more resources available to apply to solutions. Many areas of the
industrialized world already are beginning to experience constraints in
economic and social development due to water problems, and Assessment
scenarios project that the proportion of the population in developed
countries living under conditions of moderate to severe stress on water
resources could easily rise to more than half by 2025.
In short, the efficient and equitable use of freshwater
resources is a condition for progress on eliminating hunger, improving
health and advancing economic development. Poor people feel the effects
of water shortages and polluted water more severely than the rest of
humanity; conversely, action on freshwater issues is one of the key
means of advancing the goal of poverty eradication that was set at the
1995 Social Summit and in other international venues.
Conflict--and Cooperation--Over Water
As more than 300 major river basins and a number of the
major groundwater aquifers cross national boundaries, there are ample
possibilities for conflict between States, as well as within them.
But scarce water resources may also serve as a means for
domestic and international cooperation. A 1995 protocol between eight
Governments of the Southern African Development Community plans for
equitable use of shared watercourses and an integrated water resource
development programme. In Europe, the Rhine Action Plan has led to a
cleaner river and rejuvenation of several species living within it; and
Canada and the United States have been cooperating on sharing of the
waters of the Great Lakes and the prevention of pollution since the 1909
Boundary Waters Treaty between those two countries.
In the United Nations, an international convention on the
non-navigational uses of international watercourses was adopted by the
General Assembly in May 1997. The convention, which will go into force
when signed and ratified by 35 countries, sets out a framework for the
rights and obligations of upstream and downstream riparian States, and
deals with matters such as flood control, erosion, sedimentation,
saltwater intrusion and protection of aquatic life.
Recommendations for Action
Although most problems related to water quantity and
quality issues can be addressed by national and regional actions, the
authors of the Assessment maintain that anything short of a global
commitment will not achieve the goal of sustainability.
Intergovernmental dialogue on principles and means needs to be
intensified. Investment in cost-effective technologies for the
conservation and safe re-use of water needs to be stepped up, along with
transfers of technology and resources to countries with a low capacity
for coping with water scarcity and pollution.
Some countries will need to make a transition from trying
to be food self-sufficient (capable of producing all food within their
borders) to being food self-reliant (able to provide food through
purchases on the international market as well as from national sources).
In doing so, countries will become dependent on world market conditions.
Policies need to be designed to cushion the impact of increases in the
price of food on the poor, and to protect small farmers from naked
competition with international agribusiness. New options for income
generation for individuals and foreign exchange earnings for countries
will need to be created.
Pricing mechanisms for water need to be introduced which
allocate water in a way that will optimize its benefits. If the cost of
using or misusing water is not paid by the user, it will be borne by the
community at large. Under current conditions, the cost of water
shortages paid for most dearly by the poor in developing countries, who
have little access to water for sanitation and often must pay for and
carry home bottled water for personal consumption. Implementation of the
market pricing of water needs to be carefully managed in order not to
exacerbate distortion in the allocation of water resources and cause
further economic imbalance. In some cases, subsidies that will help
develop water and sanitation systems and increase efficiency in
agriculture and industry may be necessary, but the long-term aim should
be to obtain full cost recovery in all systems.
Water monitoring and assessment capabilities are quite
weak in many countries. Data on hydrological flows, water use, water
quality, demography, forestry and land management need to be harmonized
and made accessible. Education and partnerships with the private sector
and within academia are needed to bolster research capacity.
International systems for monitoring freshwater
conditions and analyzing solutions need to be matched by public opinion
campaigns designed to create the broadest social consensus on the
urgency of the issue. The overlapping interests of Governments and
industry in terms of protection of freshwater resources should be used
as the basis of private-public partnerships.
Given the lengthy period required for planning, design
and construction of large-scale water projects, as well as the time
required for ecosystems to recover from stress, concerted action needs
to be taken immediately at the local, national and international levels,
the Assessment says. Countries, working on their own, in regional groups
and with international institutions such as the United Nations, need to
develop a broad range of water strategies based on the best available
knowledge. These include incorporating water issues into development
plans and building a global trading system in which countries that lack
enough water to grow their own food will have access to crops from
water-rich regions."
According to the nonprofit
research group Ecology
Action, soil loss is a growing but potentially
reversible problem.
According to Ecology Action "Since the average person consumes
approximately 2,000 pounds of food annually, the above data can be
developed to show that approximately 8 pounds of soil were previously
lost due to wind and water erosion for each pound of food eaten.
Currently, approximately 6 pounds of soil are being lost due to wind and
water erosion per pound of food eaten annually."
Normally it takes an average of 500 years for nature to build up 1 inch
of topsoil. To grow good crops agriculturally, 6 inches of topsoil are
required. Therefore, approximately 3,000 years are needed to build up a
reasonable agricultural soil. In contrast, the 12,000 pounds per acre of
soil being lost in the U.S. on the average annually is 0.0356
inch (approximately 1/28th of an inch) of soil over 1 acre. Since only
1/500th of an inch of topsoil is being built up naturally on the
average annually in the U.S., soil is being depleted on the average
each year approximately 18 times faster than it is being built up in
nature."
According to the report of
the 2nd International Conference on Land Degradation dealing with "Social
Dimensions
of Land Degradation and Desertification,"(a conference
sponsored in part by the U.S. Department of
Agriculture's Natural Resource Conservation Service):
"Land degradation,
declines in land quality due to natural processes and anthropic
activities, is a major global issue for the 20th century and will remain
high on the international agenda even for the 21st century.
The importance of land degradation among global issues is enhanced
because of its impact on world's food security and environment quality.
The latter comprises important concerns related to eutrophication of
surface water, contamination of ground water, and emissions of trace
gases (CO2, CH4, N2O, NOx) from terrestrial/aquatic ecosystems to the
atmosphere.
Land degradation can
also be considered in terms of the loss of actual or potential
productivity or utility as a result of natural or anthropic factors.
Land degradation, is the decline in land quality or reduction in its
productivity and environmental regulatory capacity. In the context of
productivity, land degradation results from a mismatch between land
quality and land use. Land degradation processes, mechanisms that
set-in-motion the degradation trends, include physical, chemical and
biological processes. Important among physical processes are decline in
soil structure leading to crusting, compaction, erosion,
desertification, anaerobiosis, environmental pollution, and
unsustainable use of natural resources. Significant chemical processes
include acidification and leaching, salinization, and decrease in cation
retention capacity and fertility depletion. Biological processes include
reduction in total and biomass carbon, and decline in land biodiversity.
Soil structure is the important property that effects all three
degradation processes.
Factors effecting
land degradation are biophysical environments that determine the kind of
degradation processes, e.g. erosion, salinization etc. These include
land quality as affected by its intrinsic properties, climate, terrain
and landscape position, and climax vegetation and biodiversity
especially the soil biodiversity. Causes of land degradation are the
agents that determine the rate of degradation. These are biophysical
(land use and land management, including deforestation and tillage
methods), socioeconomic (e.g. land tenure, marketing, institutional
support, income and human health), and political (e.g. incentives,
political stability) forces that influence the effectiveness of
processes and factors of land degradation.
Land degradation is
a biophysical process driven by socioeconomic and political causes. High
population density is not necessarily related to land degradation. What
the population does to itself and to the land that it depends on
determine the extent of land degradation. People can be a major asset in
reversing the degradation trend. However, subsistence agriculture,
poverty and illiteracy are important causes of land and environmental
degradation. People must be healthy and politically and economically
motivated to care for the land.
Lands, depending on
their inherent characteristics and climatic conditions, range from
highly resistant or stable to extremely sensitive and fragile.
Fragility, extreme sensitivity to degradation processes, may refer to
the whole land, a degradation process (e.g. erosion) or a property (e.g.
soil structure). Stable or resistant lands do not necessarily resist
change. They are in a stable steady state condition with the new
environment. Fragile lands degrade to a new steady state under stress,
and the altered state mat be unable to support plant growth and to
perform environmental regulatory functions.
Information on the
economic impact of land degradation by different processes on a global
scale is only available for some localities. In Canada, for example,
on-farm effects of land degradation were estimated to range from $700 to
$915 million in 1984. Economic impact of land degradation is extremely
severe in densely populated South Asia, and sub-Saharan Africa.
Soil compaction is a
worldwide problem, especially with adoption of mechanized agriculture.
Severe compaction has caused yield reductions of 25 to 50% in some
regions of Europe and North America, and 40 to 90% in those of West
Africa. In Ohio, reductions in crop yields are 25% in maize, 20% in
soybeans, and 30% in oats over a 7 year period. On-farm losses due to
land compaction in the United States alone have been estimated at $1.2
billion yr-1.
Accelerated soil
erosion is another principal land degradation process. Similar to
compaction, few attempts have been made to assess the global economic
impact of erosion. On plot and field scales, erosion can cause yield
reductions of 30 to 90% in some root-restrictive shallow lands of West
Africa. Yield reductions of 20 to 40% have been measured for row crops
in Ohio and elsewhere in the Midwest USA. In the Andean region of
Colombia, workers from the University of Hohenheim, Germany, have
observed severe losses due to accelerated erosion on some lands. On a
global scale, the productivity of some lands in Africa has declined by
50% due to soil erosion and desertification. Yield reduction in Africa
due to past soil erosion may range from 2 to 40%, with a mean loss of
8.2% for the continent. If accelerated erosion continues unabated, yield
reductions by the year 2020 may be 16.5%. Annual reduction in total
production for 1989 due to accelerated erosion was 8.2 million mega
grammes for cereals, 9.2 million mega grammes for roots and tubers, and
0.6 million mega grammes for pulses. There are also serious (20%)
productivity losses due to erosion in Asia, especially in India, China,
Iran, Israel, Jordan, Lebanon, Nepal and Pakistan. In south Asia, annual
loss in productivity is estimated at 36 million tons of cereal with an
equivalent valued of $5,400 million by water erosion, and $1,800 million
due to wind erosion. It is estimated that total annual cost of erosion
from agriculture in the USA is about $44 billion yr-1, about
$100 acre-1 of cropland and pasture. On a global scale the
annual loss of 75 billion tons of soil costs (at $3 ton-1 of
soil for nutrients and $2 ton-1 of soil, for water) the world
about $400 billion yr-1, or more than $70 per person yr-1.
Nutrient depletion
is another principal process of land degradation with severe economic
impact at a global scale, especially in sub-Saharan Africa. Dutch
workers have estimated nutrient balance for 38 countries in sub-Saharan
Africa. Annual soil fertility depletion rates were estimated at 22 Kg N,
3 Kg P, and 15 Kg K ha-1. Soil erosion in Zimbabwe results in
an annual loss of N and P alone totaled $1.5 billion. In south Asia,
annual economic loss is estimated at $600 million for nutrient loss by
erosion, and $1,200 million due to soil fertility depletion.
Salt affected lands
occupy an estimated 950 million ha of land in arid and semi-arid
regions, nearly 33% of the potentially arable land area of the world.
Productivity of irrigated lands is severely threatened by build up of
salt in the root zone. In south Asia, annual economic loss is estimated
at $500 million from waterlogging, and $1,500 million due to
salinization. Potential and actual economic impact globally is not
known. Soil acidity and resultant toxicity due to high concentrations of
Al and Mn in the root zone, is a serious problem in sub-humid and humid
regions. Once again, the economic impact on a global scale is not known.
It is in the context
of the global economic and environmental impacts of land degradation and
numerous functions of value to humans that the land degradation,
desertification, and resilience concepts are relevant. They are also
important in developing technologies for reversing land degradation
trends and mitigating the greenhouse effect through land and ecosystem
restoration. Land resources are essentially non-renewable. Hence, it is
necessary to adopt a positive approach to sustainable management of
these finite resources.
Despite the
voluminous literature, land degradation remains a debatable issue. There
are two distinct schools regarding the severity and impact of land
degradation. One school believes that it is a serious global threat
posing a major challenge to the human race with regards to its adverse
impact on biomass productivity and the environment quality. Ecologists,
soil scientists and agronomists primarily support this argument. The
second school, comprising primarily economists, believes that if land
degradation were a severe issue, why have the market forces not taken it
care of? Supporters of the second school argue that land managers (e.g.,
farmers) have vested interest in their land and will not let it degrade
to the point that it is detrimental to their profit margin.
Research and
Development Issues
Land degradation as
occurring in various forms continues to pose a most serious challenge
for the very survival, well-being and future of the whole humankind.
Complicated by great uncertainty in climate change, unforeseen impact of
human activities and inner interactions among the landscape system
components, land degradation per se has become a phenomenon which
combines various environmental controls. Consequently, rehabilitation of
the degraded land must be comprehensive in nature, encompassing
physical, biological and agricultural remedial measures whose
implementation inevitably needs to be in line with what is now called
the sustainable development principle. Yet, a lack of adequate
quantitative as well as qualitative information about the causes,
processes and patterns of land degradation, a deficiency of truly
applicable rehabilitation techniques, programmes and strategies, and a
perpetual ambiguity of the meaning of sustainability in relation to
different spatial, temporal and human scales still defy efforts to solve
the degradation malaise in many parts of the world.
To meet the land
degradation challenge in the twenty-first century, a series of changes
must be made to the way how the land is viewed, what strategy should be
adopted for rehabilitation efforts and what aims should be served by the
rehabilitation endeavors. In particular, several key needs are of vital
importance:
1.
The land should always been seen in its entirety and as a
dynamic system whose resilience, recuperation and relaxation mechanisms
in response to environmental disturbances form the foundation for land
degradation and rehabilitation research. Therefore, the revelation of
all such characteristics constitutes one central task of a distinctive
land degradation science. Productivity of the land, factors affecting it
and ways to improve it should become the basis for the conception of
rehabilitation strategies and important scale controls must be duly
considered to make the strategies relevant, workable and effective.
2.
Man-land relationships should be one of harmony, mutual
nurturing and progressive development. On the micro-scale, the land
husbandry thinking may provide much of the intellectual groundwork for
how land rehabilitation can be best approached in the field; while on
the macro-scale, the sustainable development framework is essential for
a concerted global effort to combat land degradation to succeed. In both
cases, though, workable implementation strategies must be sought in the
immediate future.
3.
The problem of structurally upgrading the land economy
has not received its due consideration in past land rehabilitation
efforts and there is now a genuine need to redress the balance. The dual
images of the land as a mere resource to conserve and the land as a
versatile economic enterprise to harvest need to be carefully reconciled
in all land degradation and rehabilitation research. Perhaps, the
much-vaunted slogan of *Think globally and act locally* hangs its
success here."
A Global Issue:
Finally, researchers
Eswaran, Lal and Reich (2001) provide the following statistics on the
state of land degradation internationally: (The references for this article
can be found at this "references" link).
"Land degradation
will remain an important global issue for the 21st century because of
its adverse impact on agronomic productivity, the environment, and its
effect on food security and the quality of life. Productivity impacts of
land degradation are due to a decline in land quality on site where
degradation occurs (e.g. erosion) and off site where sediments are
deposited. However, the on-site impacts of land degradation on
productivity are easily masked due to use of additional inputs and
adoption of improved technology and have led some to question the
negative effects of desertification. The relative magnitude of economic
losses due to productivity decline versus environmental deterioration
also has created a debate. Some economists argue that the on-site impact
of soil erosion and other degradative processes are not severe enough to
warrant implementing any action plan at a national or an international
level. Land managers (farmers), they argue, should take care of the
restorative inputs needed to enhance productivity. Agronomists and soil
scientists, on the other hand, argue that land is a non-renewable
resource at a human time-scale and some adverse effects of degradative
processes on land quality are irreversible, e.g. reduction in effective
rooting depth. The masking effect of improved technology provides a
false sense of security.
The productivity of
some lands has declined by 50% due to soil erosion and desertification.
Yield reduction in Africa due to past soil erosion may range from 2 to
40%, with a mean loss of 8.2% for the continent. In South Asia, annual
loss in productivity is estimated at 36 million tons of cereal
equivalent valued at US$5,400 million by water erosion, and US$1,800
million due to wind erosion. It is estimated that the total annual cost
of erosion from agriculture in the USA is about US$44 billion per year,
i.e. about US$247 per ha of cropland and pasture. On a global scale the
annual loss of 75 billion tons of soil costs the world about US$400
billion per year, or approximately US$70 per person per year.
Only about 3% of the
global land surface can be considered as prime or Class I land and this
is not found in the tropics. Another 8% of land is in Classes II and
III. This 11% of land must feed the six billion people today and the 7.6
billion expected in 2020. Desertification is experienced on 33% of the
global land surface and affects more than one billion people, half of
whom live in Africa.
Land degradation, a
decline in land quality caused by human activities, has been a major
global issue during the 20th century and will remain high on the
international agenda in the 21st century. The importance of land
degradation among global issues is enhanced because of its impact on
world food security and quality of the environment. High population
density is not necessarily related to land degradation; it is what a
population does to the land that determines the extent of degradation.
People can be a major asset in reversing a trend towards degradation.
However, they need to be healthy and politically and economically
motivated to care for the land, as subsistence agriculture, poverty, and
illiteracy can be important causes of land and environmental
degradation.
Land degradation can
be considered in terms of the loss of actual or potential productivity
or utility as a result of natural or anthropic factors; it is the
decline in land quality or reduction in its productivity. In the context
of productivity, land degradation results from a mismatch between land
quality and land use (Beinroth et
al., 1994). Mechanisms that initiate land degradation
include physical, chemical, and biological processes (Lal, 1994).
Important among physical processes are a decline in soil structure
leading to crusting, compaction, erosion, desertification, anaerobism,
environmental pollution, and unsustainable use of natural resources.
Significant chemical processes include acidification, leaching,
salinization, decrease in cation retention capacity, and fertility
depletion. Biological processes include reduction in total and biomass
carbon, and decline in land biodiversity. The latter comprises important
concerns related to eutrophication of surface water, contamination of
groundwater, and emissions of trace gases (CO2, CH4, N2O, NOx) from
terrestrial/aquatic ecosystems to the atmosphere. Soil structure is the
important property that affects all three degradative processes. Thus,
land degradation is a biophysical process driven by socioeconomic and
political causes.
Factors of land
degradation are the biophysical processes and attributes that determine
the kind of degradative processes, e.g. erosion, salinization, etc.
These include land quality (Eswaran et al., 2000) as affected by its intrinsic properties of
climate, terrain and landscape position, climax vegetation, and
biodiversity, especially soil biodiversity. Causes of land degradation
are the agents that determine the rate of degradation. These are
biophysical (land use and land management, including deforestation and
tillage methods), socioeconomic (e.g. land tenure, marketing,
institutional support, income and human health), and political (e.g.
incentives, political stability) forces that influence the effectiveness
of processes and factors of land degradation.
Depending on their
inherent characteristics and the climate, lands vary from highly
resistant, or stable, to those that are vulnerable and extremely
sensitive to degradation. Fragility, extreme sensitivity to degradation
processes, may refer to the whole land, a degradation process (e.g.
erosion) or a property (e.g. soil structure). Stable or resistant lands
do not necessarily resist change. They are in a stable steady state
condition with the new environment. Under stress, fragile lands degrade
to a new steady state and the altered state is unfavorable to plant
growth and less capable of performing environmental regulatory
functions.
Effects of land
degradation on productivity
Information on the
economic impact of land degradation by different processes on a global
scale is not available. Some information for local and regional scales
is available and has been reviewed by Lal (1998). In Canada, for
example, on-farm effects of land degradation were estimated to range
from US$700 to US$915 million in 1984 (Girt, 1986). The economic impact
of land degradation is extremely severe in densely populated South Asia,
and sub-Saharan Africa.
On plot and field
scales, erosion can cause yield reductions of 30 to 90% in some
root-restrictive shallow lands of West Africa (Mbagwu
et al.,1984; Lal, 1987).
Yield reductions of 20 to 40% have been measured for row crops in Ohio (Fahnestock
et al., 1995) and
elsewhere in Midwest USA (Schumacher
et al., 1994). In the Andean
region of Colombia, workers from the University of Hohenheim, Germany (Ruppenthal,
1995), have observed severe losses due to accelerated erosion on some
lands. Few attempts have been made to assess the global economic impact
of erosion. The productivity of some lands in Africa (Dregne, 1990) has
declined by 50% as a result of soil erosion and desertification. Yield
reduction in Africa (Lal, 1995) due to past soil erosion may range from
2 to 40%, with a mean loss of 8.2% for the continent. If accelerated
erosion continues unabated, yield reductions by 2020 may be 16.5%.
Annual reduction in total production for 1989 due to accelerated erosion
was 8.2 million tons for cereals, 9.2 million tons for roots and tubers,
and 0.6 million tons for pulses. There are also serious (20%)
productivity losses caused by erosion in Asia, especially in India,
China, Iran, Israel, Jordan, Lebanon, Nepal, and Pakistan (Dregne,
1992). In South Asia, annual loss in productivity is estimated at 36
million tons of cereal equivalent valued at US$5,400 million by water
erosion, and US$1,800 million due to wind erosion (UNEP,
1994). It is estimated that the total annual cost of erosion from
agriculture in the USA is about US$44 billion per year, about US$247 per
ha of cropland and pasture. On a global scale the annual loss of 75
billion tons of soil costs (at US$3 per ton of soil for nutrients and
US$2 per ton of soil, for water) the world about US$400 billion per
year, or approximately US$70 per person per year (Lal, 1998).
Soil compaction is a
worldwide problem, especially with the adoption of mechanized
agriculture. It has caused yield reductions of 25 to 50% in some regions
of Europe (Ericksson et al.,
1974) and North America, and between 40 and 90% in West African
countries (Charreau, 1972; Kayombo and Lal, 1994). In Ohio, reductions
in crop yields are 25% in maize, 20% in soybeans, and 30% in oats over a
seven-year period (Lal, 1996). On-farm losses through land compaction in
the USA have been estimated at US$1.2 billion per year (Gill, 1971).
Nutrient depletion
as a form of land degradation has a severe economic impact at the global
scale, especially in sub-Saharan Africa. Stoorvogel
et al. (1993) have estimated
nutrient balances for 38 countries in sub-Saharan Africa. Annual
depletion rates of soil fertility were estimated at 22 kg N, 3 kg P, and
15 kg K ha-1. In Zimbabwe, soil erosion results in an annual loss of N
and P alone totaling US$1.5 billion. In South Asia, the annual economic
loss is estimated at US$600 million for nutrient loss by erosion, and
US$1,200 million due to soil fertility depletion (Stocking, 1986; UNEP,
1994).
An estimated 950
million ha of salt-affected lands occur in arid and semi-arid regions,
nearly 33% of the potentially arable land area of the world.
Productivity of irrigated lands is severely threatened by build up of
salt in the root zone. In South Asia, annual economic loss is estimated
at US$500 million from waterlogging, and US$1,500 million due to
salinization (UNEP, 1994). Potential and actual economic impact globally
is not known. It is not known either for soil acidity and the resultant
toxicity of high concentrations of Al and Mn in the root zone, a serious
problem in sub-humid and humid regions (Eswaran
et al., 1997a).
It is in the context
of these global economic and environmental impacts of land degradation,
and numerous functions of value to humans, that land degradation,
desertification, and resilience concepts are relevant (Eswaran, 1993).
They are also important in developing technologies for reversing land
degradation trends and mitigating the greenhouse effect through land and
ecosystem restoration. As land resources are essentially non-renewable,
it is necessary to adopt a positive approach to sustainable management
of these finite resources.
Views on land
degradation
Land degradation has
received widespread debate at the global level as evidenced by the
literature: UNEP, 1992; Johnson and Lewis, 1995; Oldeman
et al., 1992; Middleton and
Thomas, 1997; Dregne, 1992; Maingnet, 1994; Lal and Stewart, 1994; Lal
et al., 1997. At least
two distinct schools have emerged regarding the prediction, severity,
and impact of land degradation. One school believes that it is a serious
global threat posing a major challenge to humans in terms of its adverse
impact on biomass productivity and environment quality (Pimentel
et al., 1995; Dregne and
Chou, 1994). Ecologists, soil scientists, and agronomists primarily
support this argument. The second school, comprising primarily
economists, believes that if land degradation is a severe issue, why
market forces have not taken care of it. Supporters argue that land
managers (e.g. farmers) have vested interest in their land and will not
let it degrade to the point that it is detrimental to their profits (Crosson,
1997). There are a number of factors that perpetuate the debate on land
degradation:
1.
Definition:
There are numerous terms and definitions that are a source of confusion,
misunderstanding, and misinterpretation. A wide range of terms is used
in the literature, often with distinct disciplinary-oriented meaning,
and leading to misinterpretation among disciplines. Some common terms
used are soil degradation, land degradation, and desertification. While
there is a clear distinction between ‘soil’ and ‘land’ (the term land
refers to an ecosystem comprising land, landscape, terrain, vegetation,
water, climate), there is no clear distinction between the terms ‘land
degradation’ and ‘desertification’. Desertification refers to land
degradation in arid, semi-arid, and sub-humid areas due to anthropic
activities (UNEP, 1993; Darkoh, 1995). Many researchers argue that this
definition of desertification is too narrow because severe land
degradation resulting from anthropic activities can also occur in the
temperate humid regions and the humid tropics. The term ‘degradation’ or
‘desertification’ refers to irreversible decline in the ‘biological
potential’ of the land. The ‘biological potential’ in turn depends on
numerous interacting factors and is difficult to define. The confusion
is further exacerbated by the definition of ‘dryland’ where different
definitions are used. It is important to standardize the terminology,
and develop a precise, objective, and unambiguous definition accepted by
all disciplines.
2.
Extent and rate of land degradation:
Because of different definitions and terminology, a large variation in
the available statistics on the extent and rate of land degradation also
exists. Two principal sources of data include the global estimates of
desertification by Dregne and Chou (1994), and of land degradation by
the International Soil Reference and Information Centre (Oldeman
et al., 1992; Oldeman,
1994). Table 1 shows that degraded lands in dry areas of the world
amount to 3.6 billion ha or 70% of the total 5.2 billion ha of the total
land areas considered in these regions. In comparison, in Table 2,
Oldeman (1994), shows that the global extent of land degradation (by all
processes and all ecoregions) is about 1.9 billion ha. The principal
difference between the two estimates is the status of vegetation.
Although the estimates by Dregne and Chou cover only dry areas, they
also include the status of vegetation on the rangeland. Therefore, the
estimates in Tables 3 and 4 are not directly comparable. There is also a
difference in terminology used to express the severity of land
degradation. Dregne and Chou used the terms slight, moderate, severe,
and very severe to designate the severity of degradation. Oldeman used
the terms light, moderate, strong, and extreme, and these terms may not
be comparable to those of Dregne and Chou. Oldeman
et al. (1992), on the basis of expert judgment, attempted to
differentiate natural from human-induced degradation. Eswaran and Reich
(1998) attempted to evaluate vulnerability to land degradation and
desertification. Differences in terminology and approaches, and also the
areas included in the assessment, mean that the estimates of the three
workers are difficult to compare (Tables 1, 2, and 3).
|
Table 1. Estimates of all degraded lands
(in million km2) in dry areas (Dregne and
Chou, 1994). |
|
Continent |
Total area |
Degraded area † |
% degraded |
|
Africa |
14.326 |
10.458 |
73 |
|
Asia |
18.814 |
13.417 |
71 |
|
Australia and the Pacific |
7.012 |
3.759 |
54 |
|
Europe |
1.456 |
0.943 |
65 |
|
North America |
5.782 |
4.286 |
74 |
|
South America |
4.207 |
3.058 |
73 |
|
Total |
51.597 |
35.922 |
70 |
|
† Comprises land and vegetation. |
|
Table 2.
Estimates of the global extent (in million km2)
of land degradation (Oldeman, 1994). |
|
Type |
Light |
Moderate |
Strong + Extreme |
Total |
|
Water erosion |
3.43 |
5.27 |
2.24 |
10.94 |
|
Wind erosion |
2.69 |
2.54 |
0.26 |
5.49 |
|
Chemical degradation |
0.93 |
1.03 |
0.43 |
2.39 |
|
Physical degradation |
0.44 |
0.27 |
0.12 |
0.83 |
|
Total |
7.49 |
9.11 |
3.05 |
19.65 |
|
Table 3.
Vulnerability to desertification and wind and water
erosion (Eswaran and Reich, 1998). Only arid, semi-arid,
and sub-humid areas (in million km2) are
considered according to the definition of UNEP.
Estimates of water erosion include humid areas. |
|
Severity |
Desertification |
Water erosion |
Wind erosion |
|
Low |
14.653 |
17.331 |
9.250 |
|
Moderate |
13.668 |
15.373 |
6.308 |
|
High |
7.135 |
10.970 |
7.795 |
|
Very high |
7.863 |
12.196 |
9.320 |
|
Total |
43.319 |
55.870 |
32.373 |
3.
Land–vegetation
relationships: The
problem is further confounded by the definition of the term 'vegetation
degradation'. It may imply reduction in biomass, decrease in species
diversity, or decline in quality in terms of the nutritional value for
livestock and wildlife. There is a need for establishing distinct
criteria for evaluating vegetation degradation. Table 4 shows an example
of vegetation degradation in Australia, but in combination with soil
erosion. The quantity and quality of vegetation are not considered.
|
Table 4.
Vegetation degradation in pastoral areas of Australia
(Woods, 1983; Mabbutt, 1992). |
|
Type |
Area (‘000 km2) |
|
Total |
3.4 |
|
Undegraded |
1.5 |
|
Degraded |
1.9 |
|
i. Vegetation degradation with little erosion |
1.0 |
|
ii. Vegetation degradation and some erosion |
0.5 |
|
iii. Vegetation degradation and substantial
erosion |
0.3 |
|
iv. Vegetation degradation and severe erosion |
0.1 |
|
v. Dryland salinity |
0.001 |
|
Table 5.
Land degradation on cropland in Australia (Woods, 1983;
Mabbutt, 1992). |
|
Type |
Area (‘000 km2) |
|
Total |
443 |
|
Undegraded |
142 |
|
Degraded |
301 |
|
i. Water erosion |
206 |
|
ii. Wind erosion |
52 |
|
iii. Combined water and wind erosion |
42 |
|
iv. Salinity and water erosion |
0.9 |
|
v. Others |
0.5 |
-
Methods of assessment of land degradation:
Global assessment of land degradation is not an easy task, and a
wide rage of methods is used (Lal et al., 1997). Therefore,
data generated by different methods are not comparable. Further,
most statistics refer to the risks of degradation or desertification
(based on climatic factors and land use) rather than the actual
(present) state of the land. Table 3 shows vulnerability to
desertification and erosion and these estimates are much
higher than those by Dregne and Chou (Table 1) and Oldeman (Table
2), and are suggestive of the risks of land degradation. the actual
degradation may not occur because of judicious land use and advances
in land management technologies. Comparisons of these data on
different estimates shows wide variations because of different
methods and criteria used, and highlights the importance of
developing uniform criteria and standardizing methods of assessment
of land degradation.
Land
Degradation and Productivity:
A major shortcoming of the available statistics on land degradation is
the lack of cause–effect relationship between severity of degradation
and productivity. Criteria for designating different classes of land
degradation (e.g. low, moderate, high) are generally based on land
properties rather than their impact on productivity. In fact, assessing
the productivity effects of land degradation is a challenging task (Lal,
1998). Difficulties in obtaining global estimates of the impact of land
degradation on productivity in turn created problems and raised
skepticism. Table 6 from the International Board for Soil Research and
Management (IBSRAM)
indicates the problems involved in relating land degradation by erosion
to crop yield. The data from China show that despite significant
differences in cumulative soil loss and water runoff, there were no
differences in corn yield. Similar inferences can be drawn with regard
to the impact of cumulative soil erosion on yield of rice in Thailand.
Whereas soil loss ranged from 330 to 1,478 t ha-1, the corresponding
yield of rice ranged from 4.0 to 5.3 t ha-1. The lowest yield was
obtained from treatments causing the least soil loss. Crop yield is an
integrative effect of numerous variables. In addition, erosional (and
other degradative processes) effects on crop yield or biomass potential
depend on changes in land quality with respect to specific parameters.
Table 7 shows that the yield of sisal was correlated with pH, CEC, and
Al saturation but not with soil organic C and N contents. Assessing the
productivity effects of land degradation requires a thorough
understanding of the processes involved at the soil–plant–atmosphere
continuum. These processes are influenced strongly by land use and
management.
|
Table 6.
Cumulative soil loss and runoff in relation to crop
yield in three ASIALAND Sloping Lands Network countries
(Sajjapongse, 1998). |
|
Country |
Treatment |
Period |
Crop |
Soil loss
(Mg ha-1) |
Runoff(mm) |
Cumulative yield
(Mg ha-1) |
|
China |
Control † |
1992–95 |
Corn |
122 |
762 |
15.3 |
|
|
Alley cropping |
1992–95 |
Corn |
59 |
602 |
15.9 |
|
Philippines |
Control |
1990–94 |
Corn |
341 |
801 |
5.6 |
|
|
Alley cropping (low input) |
1990–94 |
Corn |
26 |
43 |
14.3 |
|
|
Alley cropping (high input) |
1990–94 |
Corn |
15 |
31 |
18.7 |
|
Thailand |
Control |
1989–95 |
Rice |
1,478 |
1,392 |
4.5 |
|
|
Hillside ditch |
1989–95 |
Rice |
134 |
446 |
4.8 |
|
|
Alley cropping |
1989–95 |
Rice |
330 |
538 |
4.0 |
|
|
Agroforestry |
1989–95 |
Rice |
850 |
872 |
5.3 |
|
† Control = Farmer’s practice |
|
Table 7.
Relationship between yield of sisal and soil fertility
(0–20 cm depth) decline in Tanga region of Tanzania (Hartemink,
1995). |
|
Land properties |
Sisal yield (Mg ha-1) |
|
Yield levels |
2.3 |
1.8 |
1.5 |
|
|
Property value |
|
pH (1:2.5 in H2O) |
6.50 |
5.40 |
5.00 |
|
Soil organic carbon (%) |
1.60 |
1.90 |
1.50 |
|
Total soil nitrogen (%) |
0.11 |
0.16 |
0.12 |
|
Cation exchange capacity (cmol kg-1) |
9.30 |
7.00 |
5.00 |
|
Al saturation (% ECEC) |
0 |
20.00 |
50.00 |
Issues and
challenges
There are sufficient
studies and reviews (e.g. Barrow, 1991; Blaikie and Brookfield, 1987;
Johnson and Lewis, 1995) that clearly demonstrate the fact that land
degradation affects all facets of life. Many issues that confront those
working in the domain of land resources include technologies to reduce
degradation and also the techniques to assess and monitor land
degradation. A number of questions remain unanswered and these include:
-
Is land
degradation inevitable?
-
Are there
adequate early warning indicators of land degradation?
-
The absence of
land tenure and the resulting lack of stewardship is a major issue
in some countries that detracts from adequate care for the land; how
can this be resolved?
-
Declining soil
quality resulting largely from human-induced degradation triggers
social unrest; what is the societal responsibility of soil
scientists?
-
How can soil
scientists better participate in developing public policy?
-
Local actions
have global impact; what are the areas for international
collaboration?
-
Who pays, who
wins in the economics of land degradation?
-
Degradation
results in loss of intergenerational equity and the value of
bequests. How do we quantify and create awareness?
-
Is there a link
between land degradation and the health of humans and animals?
-
Declining soil
quality leads to diminishing economic growth in countries where
wealth is largely agrarian. How can the rates of resource
consumption be quantified?
-
Land degradation
often destroys or reduces the natural beauty of landscapes. How
might the aesthetic value of land be quantified?
-
How to create
greater awareness of the perils of land degradation in society and
political leadership?
There are three
steps involved in the process of addressing the problem: assessment,
monitoring, and application of mitigating technologies. All three steps
are in the purview of agriculturists and specifically, soil scientists.
The latter clearly have the responsibility for soil science, and over
the past decade substantial progress has been made in communicating the
dangers of land degradation. However, much remains to be done.
Soil science has
made significant contributions to the task of soil resource assessment
but its practitioners have shown little or no interest in the additional
task of monitoring the resource base (Mermut and Eswaran, 1997). This
still remains a new area of investigation requiring guidelines,
standards, and procedures. The challenge is to adopt an internationally
acceptable procedure for this task. Soil scientists have an obligation
not only to show the spatial distribution of stressed systems but also
to provide reasonable estimates of their rates of degradation. They
should develop early warning indicators of degradation to enable them to
collaborate with others, such as social scientists, to develop and
implement mitigating technologies. Soil scientists also have a role in
assisting national decision-makers to develop appropriate land use
policies.
There are many,
usually confounding, reasons why land users permit their land to
degrade. Many of the reasons are related to societal perceptions of land
and the values they place on land. Degradation is also a slow
imperceptible process and so many people are not aware that their land
is degrading. Creating awareness and building up a sense of stewardship
are important steps in the challenge of reducing degradation.
Consequently, appropriate technology is only a partial answer. The main
solution lies in the behaviour of the farmer who is subject to economic
and social pressures of the community/country in which he/she lives.
Food security, environmental balance, and land degradation are strongly
inter-linked and each must be addressed in the context of the other to
have measurable impact. This is the challenge of the 21st century for
which we must be prepared.
Desertification
Desertification is a form of land
degradation occurring particularly, but not exclusively, in semi-arid
areas. Figure 1. indicates the areas of the world vulnerable to
desertification. The semi-arid to weakly arid areas of Africa are
particularly vulnerable as they have fragile soils, localized high
population densities, and generally a low-input form of agriculture.
About 33% of the global land surface (42 million square kilometers) is
subject to desertification. Table 8 shows the vulnerability of land to
desertification in some Asian countries. Twenty-five percent of the
region is affected and, if not addressed, the quality of life of large
sections of the population will be affected. Many of these countries
cannot afford losses in agricultural productivity. There are no good
estimates of the number of persons affected by desertification nor of
the number who directly or indirectly contribute to the process. A
recent study by Reich et al. provides some estimates for Africa.
|
Table 8.
Estimates of vulnerability to desertification in some
Asian countries. |
|
|
Countries |
Total land area (km2) |
Vulnerability to desertification |
|
|
Low |
Moderate |
High |
Very high |
|
|
Area |
% |
Area |
% |
Area |
% |
Area |
% |
|
|
Afghanistan |
647,500 |
2,954 |
0.46 |
39,088 |
6.04 |
43,838 |
6.77 |
436,480 |
67.41 |
|
|
Bangladesh |
133,910 |
85,163 |
63.60 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
Bhutan |
47,000 |
1,407 |
2.99 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
Brunei |
6,627 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
China |
9,326,410 |
262,410 |
2.81 |
239,107 |
2.56 |
65,638 |
0.70 |
72,214 |
0.77 |
|
|
India |
2,973,190 |
1,277,328 |
42.96 |
744,148 |
25.03 |
206,317 |
6.94 |
165,912 |
5.58 |
|
|
Indonesia |
1,826,440 |
29,596 |
1.62 |
46,290 |
2.53 |
5,289 |
0.29 |
232 |
0.01 |
|
|
Japan |
374,744 |
0 |
0 |
0 |
0 |
0 |
0 |
693 |
0.18 |
|
|
Cambodia |
176,520 |
45,731 |
25.91 |
118,155 |
66.94 |
0 |
0 |
0 |
0 |
|
|
Laos |
230,800 |
48,963 |
21.21 |
35,386 |
15.33 |
0 |
0 |
0 |
0 |
|
|
Malaysia |
328,550 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
Mongolia |
1,565,000 |
26,345 |
1.68 |
40,511 |
2.59 |
19 |
0 |
2,104 |
0.13 |
|
|
Myanmar |
657,740 |
130,903 |
19.90 |
140,387 |
21.34 |
20,630 |
3.14 |
13,477 |
2.05 |
|
|
Nepal |
136,800 |
20,131 |
14.72 |
8,698 |
6.36 |
0 |
0 |
228 |
0.17 |
|
|
North Korea |
120,410 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
Pakistan |
778,720 |
31,474 |
4.04 |
39,605 |
5.09 |
17,032 |
2.19 |
181,503 |
23.31 |
|
|
Papua New Guinea |
452,860 |
4,892 |
1.08 |
8,175 |
1.81 |
27 |
0.01 |
0 |
0.00 |
|
|
Philippines |
298,170 |
20,952 |
7.03 |
16,621 |
5.57 |
1,708 |
0.57 |
0 |
0.00 |
|
|
Singapore |
638 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
South Korea |
98,190 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
Sri Lanka |
64,740 |
6,337 |
9.79 |
24,393 |
37.68 |
3,421 |
5.28 |
0 |
0.00 |
|
|
Taiwan |
32,260 |
2,902 |
9.00 |
201 |
0.62 |
277 |
0.86 |
0 |
0.00 |
|
|
Thailand |
511,770 |
90,241 |
17.63 |
320,581 |
62.64 |
7,265 |
1.42 |
0 |
0.00 |
|
|
Vietnam |
325,360 |
47,516 |
14.60 |
59,238 |
18.21 |
375 |
0.12 |
0 |
0.00 |
|
|
Total |
21,115,069 |
2,135,245 |
10.11 |
1,880,584 |
8.91 |
371,836 |
1.76 |
872,843 |
4.13 |
|
As
shown in Table 9, a high population density in an area that is highly
vulnerable to desertification poses a very high risk for further land
degradation. Conversely, a low population density in an area where the
vulnerability is also low poses, in principle, a low risk. The
Mediterranean countries of North Africa are very highly prone to
desertification. In Morocco, for example, erosion is so extensive that
the petrocalcic horizon of some Palexeralfs is exposed at the surface.
In the Sahel, there are pockets of very high-risk areas. The West
African countries, with their dense populations, have a major problem to
contain the processes of land degradation. Table 10 provides the area in
each of the classes of Table 9.
About 2.5 million km2
of land are under low risk, 3.6 are under moderate risk, 4.6 are under
high risk, and 2.9 million km2 are under very high risk. The
region that has high propensity is located along the desert margins and
occupies about 5% of the landmass. It is estimated that about 22 million
people (2.9% of total population) live in this area. The low, moderate,
and high vulnerability classes occupy 14, 16, and 11% respectively and
together impact about 485 million people. Cumulatively, desertification
affects about 500 million Africans and though they have relatively good
soil resources (Eswaran et al.,
1997b,c) their productivity will be seriously undermined by land
degradation and desertification.
|
Table 9.
Matrix for risk assessment of human-induced
desertification. 1 = low risk; 2, 3 = moderate risk; 4,
5, 6 = high risk; 7, 8, 9 = very high risk. (After Reich
et al.,
1999.) |
|
|
Vulnerability class |
Population density (persons km2) |
|
|
< 10 |
11–40 |
> 41 |
|
|
Low |
1 |
3 |
6 |
|
|
Moderate |
2 |
5 |
8 |
|
|
High/Very High |
4 |
7 |
9 |
|
|
Table 10.
Land area (1,000 km2) of Africa in risk
classes. (After Reich
et al.,
1999.) |
|
|
Vulnerability class |
Population density (persons km2) |
|
|
< 10 |
11–40 |
> 40 |
|
|
Low |
2,476 |
1,005 |
750 |
|
|
Moderate |
2,608 |
1,180 |
976 |
|
|
High/very high |
2,643 |
1,074 |
825 |
|
A New Agenda
Although soils are
an ecologically important component of the environment, the availability
of research and development funds does not match their significance in
terms of the cost to society if soils become degraded. The perception
that enough is already known about soils, so that generalizations can be
made for all soils, is incorrect. There is also a failure to recognize
that agriculture is one of the major ‘stressors’ of the environment (Virmani
et al., 1994),
particularly from a soil degradation point of view (Beinroth
et al., 1994). If these
attitudes prevail, major catastrophes in the future become more
probable.
The purpose of such
discussions is to emphasize that soil is virtually a
non-renewable resource. It is
a basic philosophy that society has an obligation to protect soil,
conserve it, or even enhance its quality for future generations. The
role of society in sustaining agriculture can be demonstrated, and
conversely, the role of soil in sustaining society. The paradigms that
brought some countries of the world to agricultural affluence must be
evaluated, as well as the policies and practices that have contributed
to land degradation and decline in productivity in other countries. We
need to look at current concerns, and the urgent need to develop new
paradigms for managing soil resources, as proposed by Sanchez (1994) for
example, that will carry us through the next few decades. Some of the
valid arguments of the past now have little validity in the face of
contemporary environmental degradation. New concepts must be defined,
the research gaps identified, and the needs that will enable our
institutions to meet the challenges and requirements of the next 20
years must be indicated.
Land degradation
results from mismanagement of land and thus deals with two interlocking,
complex systems: the natural ecosystem and the human social system.
Interactions between the two systems determine the success or failure of
resource management programs. To avert the catastrophe resulting from
land degradation, which threatens many parts of the world, the following
concepts from Eswaran and Dumanski (1994) are relevant:
-
Environment and
agriculture are intrinsically linked and research and development
must address both of them.
-
Land degradation
is as much a socioeconomic problem as it is a biophysical problem.
-
Land degradation
and economic growth or lack of it (poverty) are intractably linked;
(people living in the lower part of the poverty spiral are in a weak
position to provide the stewardship necessary to sustain the
resource base. As a consequence, they move further down the poverty
spiral—a vicious cycle is set in motion).
-
Implementation
of mitigation research to manage land degradation can only succeed
if land users have control and commitment to maintain the quality of
the resources.
-
The focus of
agricultural research should shift from increasing productivity to
enhancing sustainability, recognizing that land degradation caused
by agriculture can be minimized and made compatible with the
environment.
-
Land use must
match land quality; appropriate national policies should be
implemented to ensure this occurs to reduce land degradation; (a
framework for evaluation of sustainable land management [Dumanski
et al., 1992] is a powerful tool to assess such
discrepancies and assure sustainability).
The thrust of a new
agenda for resource assessment and monitoring with respect to land
degradation (including desertification), has several components. It must
be stressed that any research and development activity should be in the
larger context of the ecosystem as addressed by Sanchez (1994) and
Greenland et al. (1994).
Components of a
national strategy to address land degradation (and desertification)
comprise:
-
Studies on
long-term water needs (quality and quantity).
-
A network of
monitoring sites to detect changes in natural resource conditions.
-
Working with
farmers by understanding and incorporating indigenous knowledge.
-
Including land
degradation aspects in research on cropping and farming systems, and
soil and water management.
-
Convincing
decision-makers that climate change, desertification, quality of
life, and sustainability are all interlinked and addressing one
helps the other.
-
Initiating
research on a new paradigm that is holistic and focuses on these
issues.
A 'scale-sensitive
information system' or database on land degradation must be made
available for the vertical network of decision-makers to enable them to
make effective policies concerning the use and management of resources.
Decision-makers at all levels of society should be able to participate
in the design and implementation of any tool that affects the social,
economic, and ecological well-being. This ensures successful
implementation of the program.
Figure 1. Desertification Vulnerability
Conclusions
Agenda 21 (UNCED,
1992, Chapter 12) emphasizes land degradation through desertification,
and the international community, particularly through UN organizations,
has launched several activities to address it. Other aspects of land
degradation only receive a casual mention in Agenda 21, and are briefly
considered in Chapter 10 under the general heading, "Integrated Approach
to the Planning and Management of Land Resources". In this sense the
problem of land degradation has been diluted and as such has not
received the global attention that it deserves. Though the stated
objective in Agenda 21 is, "to strengthen regional and global systematic
observation networks linked to the development of national systems for
the observation of land degradation and desertification caused both by
climate fluctuations and by human impact, and to identify priority areas
for action", we believe that we have yet to mobilize the soil science
community to develop a proactive programme in this area. Land
degradation remains a serious global threat but the science concerning
it contains both myths and facts. The debate is perpetuated by
confusion, misunderstanding, and misinterpretation of the available
information. Important challenges are:
-
To mobilize the scientific community
to mount an integrated programme for methods, standards, data
collection, and research networks for assessment and monitoring of
soil and land degradation.
-
There is an urgent need to address these
issues through a multi-disciplinary approach, but the most urgent need
is to develop an objective, quantifiable, and precise concept based on
scientific principles.
One
of the most definitive statements to be found on species loss can be found
at the Species Survival Commission of the
World
Conservation Union (a.k.a. The International Union for the Conservation
of Nature and Natural Resources or IUCN). For more than 40 years the IUCN
has been assessing the state of the world's plant and animal species and has
made regular reports which it calls its "Red Lists." In 2004 it
published its "Red
List of Threatened Species - A Global Species
Assessment" which was edited by
Jonathan
E.M. Baillie, Craig Hilton-Taylor and Simon N. Stuart. The Executive Summary
of that report follows, in which the writers provide a sobering perspective
on the planet's species resources.
"The
Status of Globally Threatened Species:
The
2004 IUCN
Red List
contains 15,589 species threatened with extinction.
The assessment includes species from a broad range of taxonomic groups
including vertebrates, invertebrates, plants, and fungi. However, this
figure is an underestimate of the total number of threatened species as it
is based on an assessment of less than 3% of the world’s 1.9 million
described species.
Among
major species groups, the percentage of threatened species ranges between
12% and 52%. The
IUCN
Red List identifies 12% of birds as threatened, 23% of mammals, and
32% of amphibians. Although reptiles have not been completely assessed,
the turtles and tortoises are relatively well reviewed with 42%
threatened. Fishes are also poorly represented, but roughly a third of
sharks, rays and chimaeras have been assessed and 18% of this group is
threatened. Regional case studies on freshwater fishes indicate that these
species might be more threatened than marine species. For example, 27% of
the freshwater species assessed in Eastern Africa were listed as
threatened. Of plants, only conifers and cycads have been completely
assessed with 25% and 52% threatened respectively.
The
first complete assessment of amphibians reveals that they are likely to be
the most threatened vertebrates.
Not only are amphibians significantly more threatened than other assessed
vertebrate groups, but they also have a higher proportion of species on
the verge of extinction. In total, 21% of amphibians are Critically
Endangered or Endangered, whereas the proportions for mammals and birds
are only 10% and 5% respectively. This high level of threat might be an
underestimate, as 23% of amphibians could not be assessed because
sufficient data were not available. These poorly known species are often
rare and have small distributions.
There
are major gaps in our knowledge of the status of threatened species.
While the status of vertebrates is relatively well documented (roughly 40%
assessed), we know little about non-terrestrial systems (freshwater and
marine), or many species-rich habitats (such as tropical forest or the
ocean depths), or species-rich groups such as invertebrates, plants and
fungi (which together compose the overwhelming majority of species).
Threatened
species are not randomly distributed across orders and families.
A number of families have significantly more threatened species than would
be expected on average, while others have far less. This non-random
distribution of threats across the tree of life means that entire
evolutionary lineages are liable to go extinct very quickly. For example,
of the birds, the albatrosses, cranes, parrots, pheasant, and pigeons are
significantly more threatened than other groups. Of the mammals, the
ungulates, carnivores, primates, dugongs and manatees are particularly at
risk. The salamanders, true toads, Asian tree frogs, Cameroonian stream
frogs and typical tropical American frogs among the amphibians are more
threatened than would be expected.
Extinctions
in Recent Times:
As
we learn more about the status of species, the world’s list of
extinctions continues to increase.
The IUCN Red List now contains 784 documented extinctions and 60
extinctions in the wild since 1500 AD. Over the past 20 years, 27
documented extinctions or extinctions in the wild have occurred. These
numbers certainly underestimate the true number of extinctions in historic
times as the majority of species have not been described, most described
species have not been comprehensively assessed, and proving that a species
has gone extinct can take years to decades.
Recent
extinction rates far exceed the rates of extinction in the fossil record.
Extinction rates based on known extinctions of birds, mammals and
amphibians over the past 100 years indicates that current extinction rates
are 50 to 500 times higher than extinction rates in the fossil record. If
Possibly Extinct species are included, this increases to 100 to 1,000
times natural (background) extinction rates. This is an extremely
conservative estimate, as it does not account for undocumented
extinctions. Although the estimates vary greatly, it appears that current
extinction rates are at least two to four orders of magnitude above
background rates.
Extinctions
are becoming increasingly common on continents.
While the vast majority of extinctions since 1500 AD have occurred on
oceanic islands, continental extinctions are now as common as island
extinctions. An assessment of recent extinctions indicates that roughly
50% of extinctions over the past 20 years occurred on continents. This
trend is consistent with the fact that most terrestrial threatened species
are continental.
Trends
in the Status of Threatened Species:
The
Red List Indices show that the status of birds and amphibians continues to
deteriorate. The
Red List Indices (RLIs) are an important new development, which measures
trends in extinction risk by comparing the conservation status of specific
groups over time. For birds the RLI demonstrates that their status has
deteriorated steadily since 1988, which was the year that birds were first
completely assessed. A preliminary assessment of amphibians demonstrates
similar rates of decline since 1980. However, amphibian species closest to
extinction have shown a much steeper rate of decline in status.
The
limited information available for other taxonomic groups indicates that
declines may be widespread.
Population trends are available for 260 Cycads (Cycadopsida, 288 species
in total), and of these, 79.6% (207 species) are declining, 20.4% (53
species) are stable and none are considered to be increasing.
Geography
of the Red List:
Most
threatened species occur in the tropics, especially on mountains and on
islands. Most
threatened birds, mammals, and amphibians are located on the tropical
continents: Central and South America; Africa south of the Sahara; and
tropical South and Southeast Asia. These realms contain the tropical and
subtropical moist broadleaf forests that are believed to harbour the
majority of the earth’s living terrestrial and freshwater species.
Therefore, the patterns evident for mammals, birds and amphibians are
likely to be representative of most terrestrial taxonomic groups.
The
distribution of threatened marine species is poorly known.
Of
the limited number of marine species that have been assessed, initial
findings indicate that threatened marine mammals are concentrated in the
northern Pacific Ocean and threatened seabirds, chondrichthyan fishes
(sharks, rays and chimaeras) and seahorses (the latter two not completely
assessed) in the eastern Indian Ocean and southwest and west-central
Pacific.
The
uneven distribution of threatened species means that a number of countries
have a disproportionate number of species at risk of extinction.
Countries with the most threatened and the most threatened endemic species
tend to lie within the continental tropics and countries with the highest
proportion of threatened species are mostly tropical island nations.
Countries with both a high number of threatened and threatened endemic
species include Australia, Brazil, China, Indonesia, and Mexico. Other
countries or territories holding particularly large numbers of threatened
species include Colombia, India, New Caledonia, Peru, South Africa and
Viet Nam (all of these are among the top three countries for at least one
taxonomic group) while Colombia, India, Malaysia, Myanmar, New Caledonia,
Papua New Guinea, the Philippines, South Africa, and the United States are
all among the top three countries for numbers of threatened endemics for
at least one taxonomic group. Additional countries characterized by
particularly high proportionate threat in multiple taxa include
Madagascar, São Tomé and Principe, and the Seychelles.
Patterns
of distribution of threatened species are relatively congruent between
taxonomic groups analysed.
Differences are primarily driven by underlying range-size distributions
among taxonomic groups (e.g., birds tend to have much larger range sizes
than amphibians) and by ecological limitations of specific taxa (e.g.,
birds are better able to disperse over saltwater than amphibians). Greater
variation in the distribution of threatened species is expected as more
diverse groups of species are completely assessed. For example, threatened
reptiles or cacti will likely have much greater representation in arid
areas.
The
Many Causes of the Threat:
Habitat
destruction and associated degradation and fragmentation are the greatest
threats to assessed terrestrial species.
Habitat
loss appears to be by far the most pervasive threat, impacting 86% of
threatened birds, 86% of threatened mammals and 88% of threatened
amphibians. Habitat loss will remain a dominant threat, as there is no
sign that human transformation of the landscape is slowing.
Threat
processes vary both within and between taxonomic groups.
Although
habitat destruction is universally the most dominant threat process,
birds, mammals, and amphibians are particularly vulnerable to specific
threat processes. Over-exploitation is a major threat to mammals,
impacting 33% of threatened species. For birds, over-exploitation and
invasive alien species are of similar importance, both impacting about 30%
of threatened species (although invasives are impacting 67% of threatened
birds on islands). For threatened amphibians, the major threats are
different, with 29% of species being affected by pollution (including
climate change) and 17% by disease (particularly chytridiomycosis). The
interaction between disease and extreme climatic events (drought) is the
leading hypothesis for widespread amphibian declines.
Threat
processes in the marine and freshwater systems are poorly understood.
However,
it appears that over-exploitation is presently the greatest threat to
marine species, followed by habitat loss. Incidental mortality as a result
of fisheries is an increasing threat, affecting seabirds, marine mammals,
and other marine species. Habitat loss is likely the most severe threat to
freshwater species followed by pollution and invasive species.
Threat
processes are dynamic and change over time.
Invasive alien species were historically the greatest threat to birds,
followed by over-exploitation and habitat loss. Today, habitat loss has
emerged as the dominant threat to birds, followed by invasive species and
finally over-exploitation. This order may change again if predictions of
global warming are correct.
The
Social & Economic Context of the Red List:
People
and threatened species are often concentrated in the same areas.
This is especially true in much of Asia (in particular southeast China,
the Western Ghats of India, the Himalayas, Sri Lanka, Java (Indonesia),
the Philippines and parts of Japan), and in parts of Africa (especially
the Albertine Rift in Central Africa and the Ethiopian Highlands).
The
number of threatened species is likely to rapidly increase in regions
where human population growth rates are high.
Future conflicts between the needs of threatened species and rapidly
increasing human populations are predicted to occur in Cameroon, Colombia,
Ecuador, India, Madagascar, Malaysia, Peru, Philippines, Tanzania, and
Venezuela.
Countries
that currently have a low human population density but a high rate of
population growth could be opportunistic places for pre-emptive
conservation initiatives.
For example, Bolivia, Papua New Guinea, Namibia, Angola, and the countries
of North Africa.
Countries
that have the most threatened species tend to be those that are least able
to invest significant resources in conservation.
Examples of countries with high numbers of threatened species and
relatively low Gross National Incomes (GNI) are Brazil, Cameroon, China,
Colombia, Ecuador, India, Indonesia, Madagascar, Peru, and the
Philippines. Countries with relatively strong economies but a large number
of threatened species include Argentina, Australia, Malaysia, Mexico,
United States, and Venezuela. Other countries, particularly those of
Europe, have significant financial resources but generally very few
globally threatened species.
Conservation
Responses:
Globally
threatened species frequently require a combination of conservation
responses to ensure their continued survival.
These responses encompass research, species-specific actions, site and
habitat based actions, policy responses and communication and education.
The
majority of threatened species require substantially greater action to
improve their status.
While many species already receive some conservation attention, many
others do not.
Species
can be, and many already have been, saved from extinction.
However, this requires a combination of sound research, careful
co-ordination of efforts, and, in some cases, intensive management.
Improving
the effectiveness of conservation action
requires a better understanding of the needs for such action across
species, the extent to which it is being applied, and the effects it has
had in preventing species extinctions.
The
IUCN
Red List
information can be used in many different ways as a conservation tool.
The Red List can be used to: provide information on the conservation
status of individual species; guide the listing of individual species in
national or international legislation; aid in conservation planning and
priority setting; help to identify priority species for conservation
action and recovery planning; and support educational programmes."
