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vegetation formations. It may also be a part of the denser woody vegetation in
the transition areas of forest consisting of woodlands, thicket, bushland and
scrubland. Subspecies
caffra
has also been reported as a component of the
riparian forest in Zimbabwe and South Africa (Farrell, 1968; Acocks, 1988; Hall
et al
., 2002).
There is no well-defined set of associates for subsp.
caffra
extending across the
region because of the ruggedness of the terrain and the extensive areas at
elevations above 1000 m with numerous escarpments and valleys. The Zambezi
drainage area is associated with the mopane woodland communities, with species
such as
Albizia harveyi
,
Colophospermum mopane
and
Lonchocarpus capassa
. In
the Indian Ocean north of the Limpopo basin typical species are
Acacia
nigrescens
,
L. capassa
and
Xeroderris stuhlmannii
while
Afzelia quanzensis
,
Diplorhynchus condylocarpon
,
Pseudolachnostylis maprouneifolia
and
Terminalia
sericea
are the associates most common in the miombo woodlands. Hall
et al
.
(2002) list
Dombeya rotundifolia
,
Ozoroa paniculosa
and
Pappea capensis
as the
frequent associates in the Limpopo drainage area, but these are of drier affinity
than those of the more southerly drainage into the Indian Ocean, whose associates
are of the dry forests, such as
Dialium schlechteri
,
Garcinia livingstonei
,
Sideroxylon inerme
and
Xylotheca kraussiana
. With the exception of
Pachypodium lealii
, the associates in the southern Atlantic coastal drainage are
species widespread in the dry conditions of southern tropical Africa, which are
characteristic of the Karoo-Namib regional centre of endemism.
Sclerocarya birrea
usually stands out in the farming system as it is mostly
left uncut because of its importance to the communities. It has been described
as the most prominent species because most of the vegetation associated with it
is usually of low stature (Moll and White, 1978; White, 1983; Hall
et al
., 2002).
Thus, it has widely been used as a descriptor species for plant communities in a
range of vegetation types. Hall
et al
. (2002) have attributed the lack of
quantitative information on its abundance to its being widely dispersed and
therefore very poorly represented in inventories involving small sample plots,
which are typical of ecological studies. The importance of
S. birrea
subsp.
caffra
to the system has only been reported with respect to its contribution to
stand basal area (12%) and biomass (20%) (Hall
et al
., 2002; Shackleton
et al
.,
2002). Most other studies have not mentioned the importance of the species
with respect to number of stems, height or indeed diameter classes (Hall
et al
.,
2002).
Edwards (1967) has described the
Sclerocarya
-
Acacia
'tree veld' with
subsp.
caffra
as prominent in climax vegetations in a southern African situation.
Other studies in southern Africa have also described communities where
S.
birrea
subsp.
caffra
is a dominant species in climax vegetations (Hall
et al
.,
2002). This probably confirms the importance of
S. birrea
as a descriptor
species, as discussed above.
Ecosystem functions
Sclerocarya birrea
is important in the ecology of other plants and animals as it
grows into a large tree, often a community dominant as explained earlier.
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