East African coastal forest botany - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 68

nodal nomenclature (Poore, 1962) allows for con-
inual variaion in, and incomplete knowledge of,
vegetaion. Convenient noda in a specrum of
communiies are deined by reference to one or
more of the commonest canopy species. This
terminology can be applied to patches of forest
from a few hundred square metres to several tens
of hectares and is ideal for describing the coastal
orests. The loras of coastal communiies
generally correlate with their dominant species, so
the noda povide a fleible and useul shorthand,
especially if geographical posiion is speciied as
well.
Variaion in physiognomy of coastal forest is
emphasised here by two conrasing broad desig-
naions of forest type - Dry orest and Moist for-
est - to parallel the deiniion of ecological
elements outlined above. These generic terms
help impose some order on he otherwise rather
anarchic nodal names. Riverine forest can also
often be described as Moist or Dry, depending on
the dominant trees. However, especially where
the gradaion in the vegetaion is steep or com-
plex, it is often best left unspecified as 'riverine
forest'. Although physiognomic characters are
implied in the designaion of Moist or Dry forest,
species composiion alone is a more reliable and
pracical basis for any formal summary of forest
types. However, as the forest becomes Moister
there is less of a tendency towards local
dominance and choice of a reference species
becomes more arbirary (Sterculia appendiulata is
convenient even in very mixed communiies
because of its conspicuous, smooth yellow bole).
Therefore, for the Moistest coastal forests, 'mixed
Moist forest' or simply Lowland Rain Forest are
convenient terms. The approimate relaionship
of various noda to Moomaw's (1960) and White's
(1983) terminologies is shown in Table 5.2.

Remaining patches are found in the valley bot-
toms or less steep slopes of the Pugu Hills, along
the coastal range in Kenya, at Witu in northen
Kenya and along the valley bottoms of the lime-
stone forests of the Mkulumuzi and Sigi rivers.
Moomaw noted that Sterculia-Chlorphora (Moist)
forest requires an annual rainfall of over 1000 mm
(40 inches) precipitaion, but it may also occur in
drier areas with compensaing actors, such as a
high water table.
Transects through Moist coastal fo rest in the
Pugu Hills are shown in Figures 5.5 and 5.6.
Figure 5.7 shows the variaion over a short dis-
tance between Moist and Drier forest.
Most patches of Moist coastal forest have a
high proporion of canopy ree species which lose
their leaves simultaneously during the dry season
(most emergents, but fewer lower canopy species
are deciduous). Epiphytes are abundant only by
rivers, and perhaps locally on some of the higher
hills. The range ofphysiognomy of Moist forest is
comparable to the drier extremes of White's
Guineo-Congolian rain forest. The wetter
exremes of Guineo-Congolian rain forest are not
even remotely matched by any coastal forest.
Species found n a broad range of the Moister
forest ypes include the tall, deciduous trees Anti-
ais toxicaia, Miliia excelsa and Ricinodendron
heuelotii, and the grass Olyra latifolia. These con-
situte a catholic category within the Moist orest
element, comprising 70 species in the current
sample (14%). Almost half of these Moist forest
species (see Table 5.1) are common in forest
throughout tropical Africa, especially in second-
ary forest and forest defined in other contexts
(e.g. Ghana: see Hall & Swaine, 1981) as 'Dry'.
All Moist forests are rich in Moist forest ele-
ment species. The catholic Dry forest element
also makes an important contribuion to Moist
coastal forests. However, Moist forests vary con-
siderably in the representaion of the Mariime-
Riverine element (see Figure 5.4).
Moomaw and Dale disinguish between
Sterculia-Chlorophoa rain forest and Combretum
schumannii-Cssipourea euyoies Dry orest.
However, Moist forest intermediate between
these extremes is common along the coast, par-
icularly over rocky, shallow (rendzina) soils in

Most forst

Moister forest types have a canopy of 20-35 m in
less disturbed patches and generally larger and
less sderophyllous leaves than Dry forests. Moist
forests occur on scattered coastal hills or in other
areas where precipitaion is high, or where
groundwater

and nurients are abundant.