East African coastal forest botany - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 58

(1983). Polhill (1968) and Lucas (1968) provide
florisic data for several coastal orests. Specific
forests or vegetaion types have been described by
Milne (194 7), Burtt (194 2), Welch (1960), Birch
(1963), Glover (1969, 1970), Johannson (1978),
Andrews, Grove & Home (1975), Howell (1981) ,
Rodgers et al. (1983, 1984) and Hall et al. (1984).
More recently an attempt has been made by Haw-
thone (1984) to summarise this informaion and
to relate the Tanzanian coastal forests to those of
Kenya.

(White, 1983). However, just as minor deviaions
from this ideal n the form of natural reefall gaps
and sreams are tolerable in any definiion of for-
est, so it is useful to include as part of our defini-
ion of coastal orests other vegetaion types
inimately associated with the forest proper. The
coastal forests enclose and merge with coastal
thickets and scrub forest, bushland and woodland
to such an extent that to disentangle too assidu-
ously the rue forest from the rest is to risk miss-
ing an essenial grainy heterogeneity in the coastal
forests, and certainly excludes many unusual and
rare species. Species typical of certain non-for-
ested components of the mosaic will, however, be
excluded from the sample of coastal forest species
discussed below.
Many coastal forests are sill not well known.
Forests of the offshore islands (Pemba, Mafia,
Zanzibar) do not feature in the following discus-
sion. However, from Robins (1976), Greenway et
al. (1988) and Beentje (1990) it can be deduced
that although Mafia's forest corresponds closely
to that found, for instance, at Kisiju and in part of
the Pugu Hills on the adjacent mainland, parts of
the forest communiies of Zanzibar and Pemba
include species not recorded on the mainland,
probably because of greater rainfall on Zanzibar.
Similarly, apart from informaion in Vollesen
(1980) conceing the Selous, and Moll &
White's (1978) descripion of forests further
south in the Indian Ocean coastal belt, data from
forests south of the Rufiji River are very incom-
plete. This chapter should therefore be seen as an
interim summary, pending the more complete
botanical exploraion of the coast.
Figures 5.1 and 5.2 give a summary of coastal
forests discussed here, with some neighbouring
non-coastal forests in brackets. Many small
coastal forests are not shown.

hat is a coastal forest?
The coastal forests are part of White's (1983)
Zanzibar-Inhambane regional mosaic. There is a
very broad specrum of plant communities within
this mosaic, between mangrove and other vegeta-
ion close to the sea, and higher alitude forest or
non-forest vegetaion inland. Afromontane forest
and various Somali-Masai or Zambezian vegeta-
ion ypes merge and interdigitate with the coastal
mosaic. Any deiniion of 'coastal orest' is arbi-
tray regarding delimitaion of both area, i.e. the
boundaries of the 'coast', and physiognomy, i.e.
the deiniion of orest. As this chapter should
make clear, coastal forest has no simple and
wateright definition regarding lorisic content.
For the 'coast' I have used a definiion based on
geomorphology. The coast is the land over the
sedimentary (and inrusive volcanic) rocks of t. he
coastal plains and plateau, to the east of the
eposed basement complex land. All forest in the
coast is coastal forest. Certain other lowland for-
ests, like the forest reserves at Kimboza (Rodgers
et al., 1983) or Mwanihana (Lovett, Bridson &
Thomas, 1988) and in the Usambara foothills
(Rodgers & Homewood, 1982), resemble certain
coastal orests in species composiion, yet are not
included because they occur on the basement
complex lands inland. Forests running inland
along large rivers, for example the Tana River
forests (Andrews et al., 1975; Hughes, 1990),
raverse any arbitrary borderline and again serve
to remind us that coastal forest communiies
merge gradually into those of surrounding areas.
The definiion of forest adopted here is that of
a coninuous stand of rees 10 m or more tall

Coastal orest enironment

Coastal regions of Kenya and Tanzania consist of
series of plateaux studded with hills, swamps and
rocky outcrops, and raversed by many rivers and
sreams. Throughout, there ar e farms and fallow
grassland with or without scattered rees, thickets,
coconut, mango and cashew groves, and forests in