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

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Grasslands of the world
These grasslands provide high quality, year-round grazing , as the shale-derived
soils associated with thicket are rich in nutrients.
Two important thicket types are recognized: succulent thicket and mesic
thicket. Succulent thicket occurs under semi -arid conditions (300–450 mm/
yr) and is dominated by leaf- and stem-succulent shrubs (Portulacaria afra ,
Euphorbia bothae , E. ledienii , E. coerulescens , E. tetragona , E. triangularis ,
numerous Crassula spp. and Aloe spp. ). Mesic thicket contains fewer succulents
and occurs under higher rainfall (>450 mm/yr) conditions. The cover by woody
shrubs is usually continuous , but they seldom exceed 4 m in height.
Short succulent thicket occurs in the low elevation (300–350 m) inland river
valleys of the Great Fish, Bushmans, Sundays and Gamtoos rivers. Here the
Ecca series mudstones provide a nutrient-rich substratum. The soils are shallow,
comprising arid lithosols derived from the basement rock. The valley climate is
hot and dry , with extremely high summer maximum temperatures (45°C) and
low winter minimum temperatures. In the Great Fish river valley, the structure
and composition of the “pristine” form of short succulent thicket is dominated
by Portulacaria afra , Rhigozum obovatum and Euphorbia bothae , in small (3–4 m
diameter) clumps. The vegetation in the clumps may contain emergant shrubs (e.g.
Boscia oleoides ), but they are usually