Geology Reference
In-Depth Information
subsp.
tanzaniensis,
a riverine forest liane in the
Selous Game Reserve and along the Tana and
Pangani rivers (subsp.
blpharospala,
however,
occurs in the Zambezian region).
Baphia kirkii
and
Schfleroendron usambarense
occur on both sides
of the river but, surprisingly, are not known in
Kenya.
Apart from these few specialised cases, all spe-
cies with a resricted distribuion, comprising
20%
of the sample, can be assigned to the North-
en or Southen element. Most samples of, say,
40
or more forest species either north or south of
the Msangasi River include representaives of
their respecive element (see Figure
5.4),
although Northen species are sparsely dis-
ributed in Dry forest. Some Northen or
Southen species have a very disincive form or
behaviour, giving a disincive amosphere to the
whole vegetaion. These include
Millettia puguen-
sis,
a ribbon-stemmed liane, and
Sapium
sp. nov.
(FTEA: see Hubbard
et al., 1952-83),
a sprawl-
ing, half-climbing treelet in Southen forests; and
the spiny, succulent
Euphorbia wakieldii
and
beauifully scented
Mkilua fragrans
in the North-
en forests.
coastal forests, especially those on the coastal
range south of Mombasa. Bridson
(1980)
segre-
gates the populaion of
Oyanthus pynis
there
in subsp.
longitubus,
disinct from populaions to
the south.
Dypetes usambarica
var.
mrimii
is
known only from Mrima Hill and the
kaya
forests,
and has a facies very different from other coastal
forest varieties of this species.
Diospyros shimbaen-
sis, Dichapetalum fu auosum
and
Ancistro/adus
robertsionorum
(Leonard,
1984)
are well-defined
taxa restricted to forests in this area, but their
ecology is less clear.
Sixteen per cent of the Northen element
(ND), including
Dialium oientate
and
Croton
talaeporos
(Radcliffe-Smith,
1972)
can be related
to members of the Dry forest element. These two
ree species are, however, barely forest species,
equivalent at best to the type
3
or
4
Dry forest
rees menioned above. Although most Northern
species recorded someimes in Dry orest, like
Aistogeitonia monophy/a
(see Shaw,
1971),
prefer
edaphically unusual sites,
Ticaysia ovalolia
var.
tayloii
seems a better example of a Northen Dry
forest species.
Some Northen species have close relaives
elsewhere in the Zanzibar-Inhambane regional
mosaic, but these are mostly inland from the
Southen forests. For example,
Saintpaulia rupi-
cola
(Burtt,
1948, 1958, 1964)
and
Chlamyacan-
thus linavianus
are both apparently resricted to
Moist or Riverine limestone forests, yet the close
relaives of both occur to the west or south of the
Southern coastal forests
(Saintpaulia
spp. and
.
dichrostachyus). Pavetta sp haerobotys
has different
subspecies in two of the Northen rivers (Bridson,
1978).
Other Northen species with obvious close
relaives include the apomicic
Dorstenia tayloiana
var.
tayloriana
(M. Hijman, personal communica-
ion);
Euphorbia wakieldii
from the
kaya
orests, a
sister species of
.
quadrialata
from more
southerly coastal forests (S. Holmes, personal
communicaion); and
Mitriostima greenwayi
(Bridson,
1980;
FTEA: see Hubbard
et al., 1952-
83).
Some may have only recently split from their
closest relaives
(Euphorbia wakieldit) .
Several of
these have small populaions gregarious in rocky
places and are capable of vegetaive reproducion
(Dostenia, Saintpaulia, Euphorbia, By ttneria).
The Northen element
Most
(57%)
of the Northen element are often
associated with the Mariime-Riverine element
and have an equivalent ecology within their range
(NL in Appendix
5.1).
Some are species associ-
ated strongly with rocks or rocky soils (e.g.
Euphorbia wakieldit),
or rivers (e.g.
Oystigma
msoo:
Rodgers,
1983).
As such, they are well
represented in the
Combretum-Sterulia
forests of
the limestone areas, associaions that are not
represented in the Southen forests. This sug-
gests an environmental basis for the north-south
differences.
Not all Northen species, however, are of this
broad ecological type. Tweny-one per cent (NM
in Appendix
5.1),
including
Mkilua fragrans
and
Cola porphyrantha,
are more associated with mem-
bers of the Moist forest element, though
Mkilua
may well have had its range extended (e.g. from
the Usambaras) by human influence. Most of
these are resricted to the most mixed, Moist
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