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

C.J. WILSON
The changing face of pastoral systems in grass-dominated ecosystems of eastern Africa 33
Plate 2.6
Maasai sheep grazing in a Themeda grassland, southwestern Kenya.
growth in both the highland regions and the lowland savannahs. Themeda,
Bothriochloa , Digitaria and Heteropogon mixtures are common in the open
dry savannah areas of Tanzania, such as the Serengeti plains. Short tufted
ecotypes of Themeda triandra are found at high altitudes and taller more
woody types are found in the open lowland savannahs (Rattray, 1960). These
vary in palatability, but all types quickly lose palatability with age. Themeda
triandra can tolerate light to moderate grazing , and productivity can reach
400 kg/ha/day in the wet season in the Serengeti plains, making them among
the most productive grasslands in the world (Herlocker, 1999). Plant biomass,
quality and species numbers decline in the absence of grazing, are at a peak
under moderate to high grazing (McNaughton, 1976, 1979, 1984) and can
decline under very high grazing. In the Mara region in Kenya, to the north,
which is a continuation of the grassland ecosystem of the Serengeti Plains,
Themeda makes up about 50 percent of the grass cover in lightly to moderately
grazed sites, dropping to 1–5 percent cover near settlements where Maasai
corral their livestock each night (Vuorio, Muchiru and Reid, in prep.).
The dominant grass species in the drylands of eastern Africa include Aristida ,
Cenchrus , Chrysopogon and Heteropogon . These are often found growing as
an association, the dominant species determined by the environment and
soil type . Aristida grassland is widely distributed in the dry pastoral areas of
Kenya, Ethiopia and the Sudan. Although many species are tough and have