East African coastal forest botany - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 64

Buning of coastal vegetaion has been an
annual event at least since the last century (New,
1873). Humans are the main causes of fire, for-
merly for huning but nowadays for arm
clearance. Where forest is not destroyed enirely
by ire it is often influenced by it. In Panle and
Msumbugwe Forest Reserves, for instance,
regular fires have produced a broad, highly con-
voluted border zone of vegetaion with both forest
and ire-tolerant species in close associaion. For-
est-like and thicket vegetaion occur in small
clumps in the surrounding grassland, often on
termite hills. The coastal plateau in these areas is
dominated by seasonally waterlogged black cotton
soils. It is likely that termites, drainage, fire and
the prevailing winds interact to produce the pea-
cock feather patterns in these 'forest' and thicket
clumps (Hesse, 1955; Glover, Trump & Water-
idge, 1964).
Human aciviy of one ype or another has
therefore been a pronounced and long-standing
influence on the forests. Because of the small size
of most forests and consequent high perimeter
length relaive to total area, disturbance, even if
restricted to areas near the forest edge, influences
strongly their species composiion. Many remain-
ing forest patches are, in efect, all edge. Intenal
and edge disturbance makes the forest richer in
fire-tolerant, pioneer and other sun-loving spe-
cies many of which are more pical of the vegeta-
ion surrounding the forest. This creates difficulty
in defining a strictly forest flora: the coastal for-
ests may appear as islands of vegetaion but they
are not isolated completely from their matrix.

pie, but specialised mangrove species and weedy
species someimes found on rocks were excluded.
This sample has been updated (and the categories
simplified): the 483 included taxa and a represen-
taive sample of 73 excluded species are listed in
Appendix 5 .1.
The included species have been classified
according to their distribuion within the coastal
forests and secondarily from records of the
ecology of the species elsewhere in the Zanzibar-
lnhambane regional mosaic into five major eco-
geographical elements. Some of these elements
are subdivided into more precise categories.
Addiionally, the global disribuion of each spe-
cies is summarised in crude chorological cate-
gories. The species in these ecogeographical and
chorological categories are listed in Appendix 5 .1
and summarised in Table 5.1. Fifty-two infraspe-
cific taxa (some of which would have specific rank
in the hands of different taxonomists) and a few
unnamed, but disincive plants have been
included, making a total sample of 483 plant taxa.

Chorological categoies
Chorological categories have been determined
from floras and monographs. Species, or
infraspecific taxa, are assigned to whichever of the
following categories its the disribuion best.
1. Coastal: endemic to the Indian Ocean
coastal belt (see Moll & White, 1978), or
extending (e.g. up rivers) only a short
distance from it. As well as the Zanzibar-
lnhambane regional mosaic, this zone
covers the Tongaland-Pondoland Regional
Mosaic further south.
2. Easten: extending, for instance, along
rivers to the Lake Victoria Regional
Mosaic; elsewhere in easten central
Africa, e.g. Malawi (see Dowsett-Lemaire,
1990), often in or near the Rift Valley; or
species in similar, scattered localiies not
qualifying as 4-6.
3. Ocenic: as 1 or 2 but found also on
Indian Ocean islands; including
Madagascar, but excluding offshore
islands like Zanzibar (see Vaughan &
Wiehe, 1937; Renvoize, 1976, 1979).

Floisic patens
Pattens in the coastal forest flora were examined
with a sample of species gleaned from field visits,
herbaria and the literature (Hawthorne, 1984).
From a complete and indiscriminate list of 841
species, half were excluded as they are non-forest
species, restricted to heavily disturbed forest or
forest edge. The excluded group is nevertheless a
common component of many coastal forests for
reasons outlined above. Species of riverine or
swamp forest, or species found growing over
rocks in or amongst forest, were kept in the sam-