East African coastal forest botany - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 72

coastal forests are disinguished also by the
Moist-High (MH in Appendix 5.1) forest species
within the Moist forest element. Moist-High spe-
cies such as Uvarioendron go gonis are restricted
to the few higher alitude, or higher precipitaion
coastal forests like Mrima Hill and the Shimba
Hills. However, most are widespread at similar or
higher alitudes in the forests of the basement
complex mountains like the Usambaras and Ulu-
gurus to the west, a fact noted by Verdcourt
(1980). These Moister coastal forests, therefore,
are nearly a microcosm of the coastal forest flora,
with representaives of a wide range of ecological
categories separated incompletely by habitat
specialisaion. Inevitably, though, these mixed,
Moist forests are deficient in certain geographical
elements.
Although the less specialised Moist forest spe-
cies tend to be widespread in Africa, about half of
the Moist-High species in the coastal forests are
coastal endemics, or almost so (Table 5.1).
Mariime-Riverine species often have an oceanic
distribuion, but this is less marked than might be
anicipated. The tendency for such species to be
found around the Rift Valley, in Malawi and
elsewhere in 'Easten' Africa is more marked.

types, described below. Members of the first two
types are often locally dominant, and often
characterise types of forest. Members of the
second two types are much less gregarious, but
are someimes the most important trees in
secondary forest.

1. Evergreen trees of the Caesalpiniaceae,
especially Scorophloeus isch eri and
Cy nometra webbei are typical dominants of
some tpes of Dry orest, often with
Manilkara sulcatas. These evergreen
species are often broadly associated with
each other, and are ecologically similar, so
it is convenient to extend Moomaw's
Cy nometra-Manilkara forest (below) to
include patches dominated by
Scorodophloeus ischei. Julbenardia
magnistipulata and Hy menaea verucosa are
also in some areas locally dominant, but
elsewhere occur in savanna. These
caesalpinioid dominants are often to be
found with many of their saplings
toleraing the parental shade.
Paramarolobium coeruleum seems similar to
these species but is rarer, and seems
resricted to clumps in savanna near Moist
orest.
2. Brachylaena huillensis and Manilkara discolor
are more restricted to Dry forest than pe
1. Brachylaena has been removed from
many areas for imber, but both types can
otherwise be locally very abundant.
3. Where clearings are made, deciduous
species like Erythina sacleuxii and Sterculia
schliebenii make more rapid growth and
often thrive as emergents above the
evergreen canopy.
4. Species more typical of savanna or open
woodland, like the baobab Aansonia (see
Wickens, 1982) and Ma rgaritaria discoieus,
are nevertheless often encountered as
healthy trees in coastal forests, especially
drier types. These consitute about half of
the Dry forest element trees (DX in
Appendix 5.1). Whereas type 4 species
regenerate only in medium to large gaps,
or savanna, type 3 species are typical

Dy orest

Whereas Moist forests are of sporadic occurrence
along the coast, it s likely that Dry orest ypes
previously occurred in extensive blocks. Undis-
turbed stands of Dry forest generally have a dense
canopy usually less than 20 m tall. Moomaw
(1960) notes an associaion between low phos-
phate and other nutrient levels in the Dry ever-
green forest of the Arabuko-Sokoke Forest
Reserve (a factor associated with dry forests
elsewhere: e.g. Beadle, 1962, 1966). Water supply
is also relevant and Cy nometra webberi, for
instance, a typical Dry orest ree, is avoured by
soils of impeded drainage, with an unpredictable
water supply in the Tana delta (Andrews et al.,
1975). Local dominance of one or two canopy
species is common in undisturbed stands of Dry
forest (see Figures 5.8 and 5.9).
The 32 Dry forest element canopy trees are
varied in ecology, and can be divided into four