Grasslands of the World.pdf - Disasters and Conflicts - UNEP

The changing face of pastoral systems in grass-dominated ecosystems of eastern Africa 29
northeastern Somalia . There are also few cattle in wet, southern Sudan (the
Sudd) and northern Uganda, and in the subhumid, miombo woodland regions
of southern Tanzania . Most of the cattle are in non-pastoral areas across the
region: 70 percent are in cropland and urban areas, while 30 percent are in
pastoral lands. These proportions vary strongly from country to country,
partly because of differences in amounts of high-potential land. For example,
about 35 percent of Kenya is high potential and 80 percent of the nation’s cattle
herd resides there. In contrast, there is very little high-potential land in Somalia
and Djibouti and thus all the cattle live in drylands in those countries.
A previous global analysis of pastoral systems (from Reid et al., 2003)
has been used to estimate the extent of grass -dominated pastoral systems in
eastern Africa . This pastoral systems map (Figure 2.7) was created using four
Geographical Information System (GIS ) data layers: land cover (USGS/EDC,
1999; Loveland et al., 2000), length of growing period (Fischer, Velthuizen
and Nachtergaele, 2000), rainfall (IWMI, 2001; Jones and Thornton, 2003) and
human population density for Africa (Deichmann, 1996).
Initially, land cover, length of growing period and human population maps
were used to establish the location of all cultivatable land (>60 growing days), all
land cover currently under crops in the USGS coverage (dryland cropland and
pasture ; irrigated cropland and pasture; mixed dryland and irrigated cropland
and pasture; cropland and grassland mosaic; and cropland and woodland
mosaic) and any other areas with sufficient human population (>20 people/
km 2 ) to exclude extensive rangeland use (for details, see Reid et al., 2000a;
Thornton et al., 2002). This classification thus joined all but the most extensive
agropastoral systems with cropland, and maps about 9 percent more cropland
than is in the USGS database. “Urban” included all areas with more than
450 people/km 2 . The remaining areas (not cultivatable, low human population
density) were discriminated into pastoral system classes by mean annual rainfall
as follows: areas receiving less than 50 mm of rainfall were classified as hyperarid
; areas with 51–300 mm were arid; and areas with 301–600 mm were semi -
arid . Highland areas were those with temperatures of more than 5°C but less
than 20°C during the growing season, or less than 20°C for one month a year.
Most of eastern Africa ’s pastoral systems are semi -arid (34 percent), with
much smaller areas of arid (12 percent), hyper-arid (8 percent), humid to subhumid
(9 percent), and temperate and highland (1 percent) pastoral systems
(Figure 2.7). Cropland and urban areas cover 27 percent of the region. Only
Sudan has the driest (hyper-arid) pastoral systems, while eastern Eritrea ,
northern Ethiopia, Djibouti, Somalia and northern Kenya support extensive
arid pastoral systems. The most common land cover type in Kenya, Somalia,
Ethiopia and Sudan is semi-arid rangeland. Tanzania , Uganda and Sudan have
the most extensive wet pastoral systems.
By comparing potential vegetation (Figure 2.3) and pastoral and cropland
systems (Figure 2.7), we can see what types of vegetation farmers have pre-