TheImprovement ofTropical and Subtropical Rangelands

16 IMPROVEMENT OF TROPICAL AND SUBTROPICAL RANGELANDS
TABLE 2 CatU. PopulaUona In the W..t African Sah.l
Number of CaUl. (in thouaand.)
Country 1940
1968-1Q70 lQ74
lQ78 1982 lQ86
Senecal 440 2,616
Mauritania 860 2,100
Mali 1,174 6,SOO
Burkina 491 2,lKXl
Nicer 764 4,200
2,318
1,175
3,640
2,SOO
2,200
2,600 2,300 2,200
1,200 1,600 1,360
3,800 6,SOO 6,800
2,600 2,871 2,800
2,860 3,487 3,630
Total 3,700 17,116 11,633 12,960 16,468 16,680
SOURCES: Gallai., 1979; Africa South of the Sahara lQ86 1986; and Africa
South of the Sahara 1988 1987.
that time, widespread environmental degradation has dramatically
reduced the availability of the natural products 8880ciated 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).
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 ofthe 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
Mrican 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).