(introduction...)
In this report, rangelands are defined as "land carrying natural
or semi-natural vegetation which provides a habitat suitable for herds of wild
or domestic ungulates" (Pratt, Greenway, and Gwynne, 1966). Rangelands typically
possess characteristics that make them unsuitable for agriculture or intensive
forestry: they are variously too dry, too steep, too rocky, poorly drained, or
too remote. In Africa, the Near East, and southern Asia - the geographical focus
of this report - rangelands occupy 2,666 million hectares, or 53 percent of the
land surface (table 1).
In the areas considered, there are two general systems of
rangeland utilization: systems that use the land to produce goods that are
removed or exported from the land (ranches), and those that chiefly provide
subsistence for people associated with livestock and wildlife populations
(indigenous pastoral systems). Contrary to popular belief in industrial nations,
pastoral systems are not necessarily less productive than ranching systems.
African pastoral systems, for example, are often as productive as
market-oriented ranching systems in comparable areas in terms of protein
produced per unit of land utilized.

Table 1 Distribution of the World's
Pastures and Rangelands, 1955-83
Most ranches are privately owned, and characteristically use
investments of capital and various management techniques on large areas of land
to increase livestock production. Unlike pastoral systems, labor inputs are low.
Hence, ranching often produces more protein per hour of labor than does
pastoralism. On the other hand, ranching requires vastly greater inputs of
energy, and expenses incurred in connection with fencing, water development,
brush control, revegetation, grazing management, and selective breeding are
substantial.
Pastoral systems represent the principal form of rangeland
utilization in Africa and Asia. They involve significant social adaptations to
the movement of livestock or wildlife from one location to another in relation
to the availability of forage and water. The rangelands utilized are seldom
privately owned, and mechanical and chemical inputs are seldom prominent. The
systems are labor intensive. It has been estimated that livestock and wildlife
support some 30-40 million pastoralists, and the animals and animal products
associated with pastoral systems are critical to millions of other individuals
in settled communities (International Institute for Environment and Development
and the World Resources Institute, 1987).
The importance of livestock in pastoral systems exceeds their
value as sources of milk, meat, blood, and hides. Livestock often represent a
means of accumulating capital and, in some societies, are associated with social
status. They are assets that can reproduce and that can be liquidated should
cash be required. In addition to supporting livestock, rangelands serve as
sources of other significant economic products: bushmeat, fruits, berries, nuts,
leaves, flowers, tubers, and other food for human populations, as well as
medicinal plants, building materials, thatch, fencing, gums, tannin, incense,
and other products important to the economies of rural populations (Sale, 1981;
National Research Council, 1983; Malhotra, Khomne, and Gadgil, 1983).
The importance of rangelands as sources of bushmeat and
vegetable foods for human populations deserves special attention. These foods
are derived from species that are well adapted to the environmental
peculiarities of the regions in which they are found. Hence, such foods are
often available in the event of crop failure or substantial losses of livestock.
Even during periods with average rainfall, satisfactory crop yields, and herd
stability, such foods constituted a significant part of local diets. Indeed, in
many societies, the offtake of wildlife from rangelands exceeds that of
livestock in importance. In 1959, for example, the sedentary and pastoral
peoples of the Senegal River Valley in West Africa relied upon fish and wildlife
for over 85 percent of the meat that they consumed (Cremoux, 1963); native
plants were of equal or greater importance. Since that time, widespread
environmental degradation has dramatically reduced the availability of the
natural products associated with local coping strategies and has correspondingly
increased the vulnerability of rural populations (National Research Council,
1983). In most instances, the degradation is a result of breakdowns in the
traditional resource management systems that for centuries had maintained an
equilibrium between environmental systems and human activity (National Research
Council, 1986).

TABLE 2 Cattle Populations in the
West African Sahel
TABLE 2 Cattle Populations in the West African Sahel
Number of Cattle (in thousands) |
Country |
1940 |
1968-1970 |
1974 |
1978 |
1982 |
1985 |
Senegal |
440 |
2,615 |
2,318 |
2,500 |
2,300 |
2,200 |
Mauritania |
850 |
2,100 |
1,175 |
1,200 |
1,500 |
1,350 |
Mali |
1,174 |
5,300 |
3,640 |
3,800 |
5,300 |
5,800 |
Burkina |
491 |
2,900 |
2,300 |
2,600 |
2,871 |
2,800 |
Niger |
754 |
4,200 |
2,200 |
2,850 |
3,487 |
3,530 |
Total |
3,709 |
17,115 |
11,633 |
12,950 |
15,458 |
15,680 |
SOURCES: Gallais, 1979; Africa South of the Sahara 1986 1985;
and Africa
South of the Sahara 1988 1987.
Rangeland ecosystems, particularly those in arid and semiarid
regions, are highly susceptible to degradation. In many regions, degradation is
chiefly a result of changing herd composition and overstocking. Particularly
noteworthy since the advent of the colonial period has been a proportional shift
in herd inventories favoring cattle, a form of livestock poorly adapted to
dryland ecosystems, at the expense of well-adapted and less environmentally
destructive forms, such as camels, as the former were more marketable within the
context of the new economic order (Chassey, 1978). In the West African Sahel,
for example, colonial policy resulted in an almost fivefold increase in cattle
populations between 1940 and 1968 (table 2).
Agricultural expansion has also contributed to the degradation
of tropical and subtropical rangelands. In drylands, agricultural expansion
results in increased pressure on rangelands because the conversion of the more
productive forage reserves to crop land forces pastoralists to "overgraze" the
remaining land base (Thomas, 1980).
Moreover, grain crops deplete soil nutrients at a rate thirty
times greater than the rate of nutrient loss in a properly stocked range
ecosystem (Heady, 1975). The cost of replacing the lost phosphorus, potassium,
nitrogen, and other nutrients is generally prohibitive.
In many regions, high levels of sustained use pressure have
eliminated the more palatable plant species (species referred to as "decreasers"
in range science). In dryland ecosystems, plant growth is relatively slow. When
aerial biomass is consumed by foraging livestock, many plants respond by
transferring nutrients from their roots in order to produce new leaves. This
results in reduced rooting. Reduced rooting, in turn, reduces the ability of the
plant to absorb moisture and nutrients even during rains. As the more palatable
species are weakened, less palatable species ("increasers") become dominant.
With continuing high levels of use pressure, increasers give way to undesirable
shrubs, grasses, and forbs ("invaders"). As these species are overgrazed, the
land surface is exposed to further, more severe, degradation. In the drylands of
Africa and Asia, cattle have been particularly destructive. Unlike camels and
goats and most native herbivores, which are predominantly browsers, cattle are
grazers. Cattle therefore increase pressure upon perennial grasses and often
eliminate them, causing ecological deflections toward ephemeral annual grasses
and relatively unproductive trees and shrubs, such as Calotropis procera (Gaston
and Dulieu, 1976).
The reduction or elimination of vegetative cover, in combination
with trampling and the compaction of the surface by livestock, reduces
infiltration and permits the mobilization of soil particles subject to transport
by overland flow. This results in depressed groundwater tables and increased
soil erosion. Surface exposure and the reduced organic content of soils also
result in altered soil-water relationships and greater amplitude in soil
temperatures. This altered soil ecology adversely affects important soil
microorganisms, such as the rhizobial bacteria responsible for nitrogen fixation
in acacias and other leguminous genera. This, in turn, affects nutrient regimes
and results in a further loss of soil structure. Altered soil ecology directly
eliminates additional plant species and frustrates regenerative processes in
others. Further losses occur through disruptions in various biological
dependency and affinity relationships. Environmental degradation both reduces
range carrying capacity for livestock and affects wildlife populations through
habitat modification. Rangeland conditions in selected countries of Africa,
Asia, and Western Asia are described in tables 3, 4, and 5.

Table 3 Rangelands Conditions in
Selected African Countries

Table 3 Rangelands Conditions in
Selected African Countries - continue 1

Table 3 Rangelands Conditions in
Selected African Countries - continue 2

Table 3 Rangelands Conditions in
Selected African Countries - continue 3

Table 4 Rangeland Conditions in
Selected Western Asian Countries

Table 4 Rangeland Conditions in
Selected Western Asian Countries - continue 1

Table 4 Rangeland Conditions in
Selected Western Asian Countries - continue 2

Table 4 Rangeland Conditions in
Selected Western Asian Countries - continue 3

Table 5 Rangeland conditions in
selected Asian countries

Table 5 Rangeland conditions in
selected Asian countries - continue 1
The effects of rangeland degradation often extend well beyond
the rangelands themselves. Dust originating in degraded rangelands is
transported by dry-season winds to distant areas, causing annoyance, health
hazards, and costly interruptions in air and ground traffic. The rapid release
of runoff in degraded rangelands following rains contributes greatly to
destructive flooding in downstream lowlands, and sediment entering drainage
systems in degraded rangelands shortens the useful life of reservoirs and
irrigation systems.
Less obvious effects would include the impact of rangeland
devegetation on climatic regimes. For example, it is now widely believed that
precipitation is strongly influenced by biogeophysical feedback mechanisms
(Charney, 1975). According to this hypothesis, drought is reinforced through
changes in vegetative cover. Large-scale losses of vegetation would increase
surface albedo, which, in turn, would affect the atmospheric energy budget in
such a way that the subsidence, which promotes aridity, would be intensified.
Further, it is now believed that levels of precipitation are
strongly influenced by soil moisture locally released into the atmosphere
through evapotranspiration. Hence, reduced vegetative cover and decreased soil
moisture would result in reduced local precipitation. Finally, losses of
vegetation affect surface roughness in the atmospheric boundary layer. Surface
roughness contributes to the destabilization of moisture-laden air masses, thus
encouraging precipitation. Devegetation also reduces carbon dioxide uptake in
the planetary biomass. The greater concentration of carbon dioxide in the
atmosphere contributes to global warming, causing changes in atmospheric
circulation and rising sea levels through the melting of continental ice sheets
(Study of Man's Impact on Climate, 1971; Woodwell, 1984).
The science of range management originated in North America, and
North American approaches to range management are described in several wellknown
volumes, such as A. W. Sampson (1952), Stoddart and Smith (1955), R. R. Humphrey
(1962), and National Research Council (1962, 1984). Historically, attempts to
transfer experience gained in the management of North American or Europe an
rangelands to the management of tropical and subtropical rangelands have been
unsuccessful (Heady and Heady, 1982). In improving tropical and subtropical
rangelands, it is important to carefully characterize the physical system being
managed in order to better understand the biological potential of the system and
assure that critical ecological processes are restored and maintained. It is
equally important to relate efforts in range improvement to the needs,
knowledge, adaptations, and capabilities of local populations,
as well as to the broader economic and political contexts of such efforts. The
widespread belief that pastoral systems are simply artifacts of the past
requires reexamination. The view that range improvement in the tropics and
subtropics should focus narrowly upon the increased per unit productivity of
selected forms of livestock, usually cattle, at the expense of the biological
diversity basic to the maintenance of local coping strategies and economies
should similarly be reexamined. This report describes tropical and subtropical
rangelands, addresses issues of socioeconomic context, discusses approaches to
regional assessment and site evaluation, explores management strategies, and
provides criteria for plant selection in relation to efforts in range
improvement. The case studies appended to the report provide further information
regarding these issues. The Improvement of Tropical and Subtropical Rangelands
is the third report to appear in the series, "Resource Management for Arid and
Semiarid Regions." Other titles include Environmental Change in the West African
Sahel (1983) and Agroforestry in the West African Sahel
(1983).