Geology Reference
In-Depth Information
Table 4 .1.
Numbes of speies ocroing in dffrent
Easten Arcorest pes with westery distributions.
274 sp ecies were inlued in the anaysis, of which
169 or 62% have westery distibutions
occurs from south of the Zambezi River to the
central Easten Arc; it is replaced in the Kivu-
Rwenzori highlands by subsp.
montana,
and by 70
other
Trichosypha
species further west. Some of
the replacement species are markedly disjunct
with their relaives.
Cy licomopha pavlora
occurs
from northen Malawi to the Kenyan highlands;
the only other member of the genus is
. solmsii
from Cameroun.
Balthsaria schliebenii
occurs in
the northen and cenral Easten Arc and the
Kivu-Rwenzori highlands, the only other member
of the genus
B. mannii
is found in Sao Tome.
Many Eastern Arc endemics are in otherwise
exclusively westen Guineo-Congolian genera,
for example
Enantia, Cincinnobotys, Poycerato-
carpus
and
Oaoknema.
At the family level, the
monotypic Easten Arc genus
Cphalosphara,
in
the Myrisicaceae, is the only member of the
family occurring east of the arid corridor and
represented in the westen Guineo-Congolian
region by
Coelocayon, Py nanthus, Sphocphalium
and
Staudtia.
In contrast to southen moist orests, where
there are relaively ew species not ound in the
Easten Arc (ith the excepion of the unique
Cape forest edge flora: Phillipson
&
Russell,
1988), there are many widespread westen
Guineo-Congolian species that do not reach the
Easten Arc. Most of these, or example
Anthonotha noleae, Klainoxa gabonensis
and
Maesopsis eminii,
only extend as far east as the
great lakes of Tanganyika and Victoria and so do
not cross the arid corridor of low rainfall which
runs from northeast Africa through cenral
Tanzania to the Namib Desert (Werger, 1978).
However,
Tich ilia prieuiena
reaches Mbeya
Mountain and
Neoboutonia melei
reaches north-
en Lake Nyasa.
Maesopsis eminii
has been inro-
duced into the East Usambara Mountains, where
it is readily dispersed by hombills and has rapidly
become naturalised through invasion of gaps in
indigenous forest. This suggests a historical,
rather than climaic or edaphic, reason or the
absence of these widespread westen Guineļ¾
Congolian species.
The srong affiniies between the Easten Arc
and westen Guineo-Congolian region must
largely pre-date mid-Teriary uplift of the cenral
Number of species
a
Forest type
2a
2b
Dy lowland
27
10
34
Lowland
39
10
42
Submontane
43
14
48
Montane
43
37
78
Upper montane
19
10
28
Dy montane
27
22
49
155
Total species
102
67
Note:
a
l. West ofthe eastern Zaire highlands.
2a. West of the arid corridor but not extending west of
the eastern Zaire highlands.
2b. West of the arid corridor.
lanceolata, Newtonia buchananii, Ritchiea albesii
and
Xy malos monospora
in montane forests. In
contrast to the widespread species, there are a
number of trees with remarkably disjunct dis-
ribuions between West and easten Africa.
These include
Mesoyne insignis, Paramacrolobium
coerueum
and
Schflerodendron usambarense
in
lowland forest; and
Te nstroemia poypetala
in
upper montane forest.
Other species have easten distribuions but are
replaced by closely related species in the westen
Guineo-Congolian region. For example,
Anin-
geia aoi-fi ederiii
occurs from the Hom of
Africa to south of the Zambezi River and in the
Kivu-Rwenzori highlands, but is replaced in the
main part of the Guineo-Congolian region by
A.
altissima
and
A. robusta.
Similarly,
My ianthus hol-
stii
occurs from south of the Zambezi River to the
Kenyan and Kivu-Rwenzori highlands, but is
replaced further west by six other species of
My ianthus
(de Ruiter, 1976) one of which,
M.
preusii
subsp.
seretii,
also extends to easten Africa
(Berg
&
Hijman, 1989).
Neoboutonia macrocalyx
occurs rom southen Malawi to the Kenyan and
Kivu-Rwenzori highlands, but is replaced by .
mannii
and the very widespread .
mellei
to the
west.
Tichospha uluurensis
subsp.
uluurensis
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