Agriculture Reference
In-Depth Information
The loss of habitat of the indigenous fruit trees due to expansion of
agriculture and deforestation calls for management strategies appropriate for
natural populations, including those on farm land. Hall
et al
. (2002) have
suggested that the effective management of such populations must incorporate
the ecology of the particular species. This chapter will consider the ecology and
biology of
S. birrea
,
U. kirkiana
and
S. cocculoides
in southern Africa.
18.2 Ecology and Biology of the Species
18.2.1
Sclerocarya birrea
Sclerocarya birrea
is a member of the Anacardiaceae (cashew family), along
with 650 species and 70 genera of mainly tropical or subtropical evergreen or
deciduous trees, shrubs and woody vines. Three subspecies of
S. birrea
are
recognized:
S. birrea
subsp.
caffra
(Sond.) Kokwaro;
S. birrea
subsp.
multifoliolata
(Engl.) Kokwaro; and
S. birrea
subsp
. birrea
. The subspecies
multifoliolata
occurs in mixed deciduous woodland and wooded grassland in
Tanzania (Shackleton
et al
., 2002) while
birrea
occurs through west, north-east
and east tropical Africa across a range of vegetation types, principally mixed
deciduous woodland, wooded grassland and through the open dry savannahs
of northern tropical Africa and the Sahelian region (Hall
et al
., 2002). The most
important subspecies in southern Africa is
caffra
.
Ecology
Despite the ubiquitous distribution and household and commercial importance
of
S. birrea
subsp.
caffra
in southern Africa, there has been very little
autecological research on the species (Shackleton
et al
., 2002).
S. birrea
is one
of the two species of
Sclerocarya
, the other being
Sclerocarya gillettii
Kokwaro,
which is restricted to a small area of arid eastern Kenya (Hall
et al
., 2002). The
review by Hall
et al
. (2002) seems to consolidate the fact that
Sclerocarya
has
its origins in Africa. Archaeological evidence indicates that the fruits of
S. birrea
subsp.
caffra
were known and consumed by humans in 10,000
BC
(AFT
Database).
S. birrea
is usually dioecious, a mechanism that ensures no selfing,
although male and female flowers occasionally occur on the same tree
(hermaphroditism). Elephants are thought to be the major dispersal agent.
Other agents are humans, goats and monkeys.
Sclerocarya birrea
is widely distributed across the sub-Saharan Africa,
including but not restricted to the miombo woodland ecosystem stretching from
Senegal to Ethiopia in the north, southward to Natal in South Africa, and
eastward to Namibia, Angola and the southern part of the Democratic Republic
of Congo. Hall
et al
. (2002) provide the most detailed distribution maps with
respect to environmental factors such as elevation and rainfall. The species is
associated with seasonal rainfall patterns, with a mean annual rainfall of
500-1250 mm. Subspecies
caffra
has been reported in more humid areas
(1200-1600 mm rainfall) in transition areas between the Guineo-Congolian
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