Geology Reference
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genus of which is the Malagasy
Cedrelopsis.
It may
well be that some Easten Arc species with
southerly distribuions, notably those of drier for-
est ypes, have their origins in Madagascar rather
than a specifically Cape flora.
The Cape flora itself has ropical affiniies. For
example, Proteaceae, which are well represented
in southen Africa and occur in upper montane
and dry montane Easten Arc moist forests as
Faurea,
probably evolved rom ropical African
and Madagascan ancestors (Goldblatt, 1978).
Another dry upper montane forest genus,
Olinia,
has its centre of diversity in southen Africa with
four species: the widespread
0.
rochetiana
occurs
in the Easten Arc, and the other three are found
south of the Zambezi River with two of these only
found south of the Limpopo River.
Olinia
may be
a ropical African genus which has diversified in
the Cape (Goldblatt, 1978), iving rise to the
southen endemic family Penaeaceae. Similarly,
Goldblatt suggests that ypical Cape elements in
the Rutaceae-Diosmeae and Thymeleaceae could
have evolved from more primiive broadleaved
tropical ancestors such as
Caloendom
(Rutaceae)
and
Pediea
(Thymelaceae), both of which are
found in dry montane forest. An herbaceous
genus commonly found in moist forests,
Strptocarpus,
which has diversified in Natal, is
also thought to have a tropical origin (Hilliard
&
Burtt, 1971).
The lowland Easten Arc and easten African
coastal forest flora which extends southwards is
primarily westen Guineo-Congolian and Mada-
gascan (or further easten) in origin and affiniy
rather than southen African. It has many
endemic species in Guineo-Congolian genera
and many widespread Guineo-Congolian species
(Moll & White, 1978). Thus both lowland and
upland Easten Arc orests do not have a strong
southen affinity or origin, and the southen or-
ests themselves are predominately of tropical
origin. Southen temperate moist forests suffered
severely during the Miocene desiccaion of the
Cape. For example, fossil records eist from there
of subtropical forest families such as Winteraceae
and Sarcolaenaceae (Coetzee & Muller, 1984)
which are no longer represented on coninental
Africa. The upwelling of cold waters, that con-
situte the present Benguela current and which
bring aridity to southwest Africa, began in the
early late Miocene about 10 Myr
BP
(Siesser,
1980). This was before the rejuvenaion of the
Easten Arc faults about 7 Myr
BP
(Griffiths,
Chapter 2) and creaion of high mountains on the
eroded African land surface. As there were no
high mountains, southern subtropical species
were unable to survive the Miocene desiccaion in
tropical montane refugia with temperate climates.
However, some montane tropical taxa sub-
sequently dispersed souh into the temperate zone
and radiated into the remarkable Cape flora.
Ainities with the noth
Afiniies ith the north are not as strong as those
to the west and south with 52% of Easten Arc
tree species occurring to the north compared with
61 % to the south and 62% to the west (Table
4.3). Of the 86 species which occur in the Hom of
Table 4.3.
Numbes of sp ecies occurring in dferent
Easten Arc orest ty pes with nothery distibutions.
274 sp ecies were inluded in the anaysis, of which
143 or 52 % have northerly distributions
a
Number of species
Forest type
2a
2b
3a
3b
Dry lowland
22
8
23
4
22
Lowland
23
9
21
5
23
Submontane
35
20
17
5
27
Montane
45
24
66
8
64
Upper montane
19
6
25
1
21
Dry montane
36
11
4
7
2
39
Total
86
42
115
15
92
Note:
0
1. Hom of Africa (including southwest
Ethiopia).
2a. Cenral Kenyan highlands, but not the Hom of
Africa.
2b. Central Kenyan highlands, and also the Horn of
Africa.
3a. Northern Tanzanian volcanics, but not the central
Kenyan highlands and Horn of Africa.
3b. Northern Tanzanian volcanics, and also the central
Kenyan highlands and Horn of Africa.
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