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and Zambezian regions and in parts of Madagascar (Hall
et al
., 2002).
Subspecies
caffra
is usually associated with lower temperatures because of the
high elevations common in eastern Africa, and the inclusion of higher latitudes
in the range of the species means that it is often subject to lower mean annual
potential evapotranspiration values (1100-1700 mm; Hall
et al
., 2002). Most
trees of the species occur in the frost-free part of its range but the populations
in south-east Zimbabwe and south into South Africa experience occasional
frost. While
S. birrea
occurs through most of sub-Saharan Africa, the different
subspecies occupy different parts of this range. However, all the subspecies
occur together only in northern Tanzania, which is the southern limit for subsp.
birrea
. Subspecies c
affra
is the most widespread and occurs in eastern Africa
(Kenya, Tanzania), southern Africa (Angola, Malawi, Mozambique, Zambia and
Zimbabwe) and southern Africa (Botswana, Namibia, South Africa and
Swaziland) and is also recorded from Madagascar (Fox and Norwood Young,
1982; Arnold and de Wet, 1993; SEPASAL Database, 2001; Shackeleton
et al
.,
2002). The southern end of its range is the coastal belt of southern KwaZulu-
Natal in South Africa, near Port Shepstone at approximately 31° S (Hall
et al
.,
2002; Shackleton
et al
., 2002). Within South Africa, it is common in the
savannah areas of northern KwaZulu-Natal, Mpumalanga, northern and north-
west provinces. Subspecies
caffra
has been introduced either for experimental
purposes or as an ornamental in Israel, Mauritius, Florida (USA), India and
Oman (Hall
et al
., 2002). Using random amplified polymorphic DNA (RAPD)
analysis of 16 populations, Kadu
et al
. (2006) confirmed the hypothesis that
the evolution of
S. birrea
is complex, with different contributions of seed and
pollen in determining gene flow, and they found that Tanzania contained most
chloroplast haplotypes.
Subspecies
caffra
rarely occurs in areas of lower rainfall, though it does
occur in the Petersburg plateau where rainfall is 350-400 mm. It prefers well-
drained, sandy, loamy soils, appearing to be generally intolerant of frost. The
species has been reported to be associated with sandy-textured soils and in
some cases sandy loam and loam soils. In other parts of southern Africa, heavy
clayey basaltic soils have been reported to support subsp.
caffra
(Shackleton
and Scholes, 2000; Hall
et al
., 2002). Subspecies
caffra
grows on soils of
variable fertility; in Malawi it grows in the fertile Shire valley and in the
mopanosols. Indeed, the subspecies has been reported as an indicator of fertile
soils (Hall
et al
., 2002).
White's framework (Hall
et al
., 2002), used in the consideration of the
vegetation in which
S. birrea
occurs, is based on 20 phytochoria.
S. birrea
extends to most of these 20 phytochoria. However, in continental Africa most of
the range falls within the vast Sudanian and Zambezian regional centres of
endemism and the more equatorial of the two East African coastal mosaics
(Zanzibar-Inhambane) adjoining the latter. Subspecies
caffra
occurs in the
southern phytochoria (Hall
et al
., 2002). As a consequence of the concentration
of the
Sclerocarya
species in the drier parts of Zambezian and Sudanian regional
centres, which are respectively dominated by the
Brachystegia
-
Julbernardia
(miombo) and
Isoberlinia
woodlands, the species is of less importance in these
areas. In general
S. birrea
grows in wooded grassland, grassland and parkland
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