Eastern Arc moist forest flora - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 36

limits, which does have temperate
affiniies, a act that was recognised in the
last century for West Africa (Hooker,
1861, 1864) and confirmed in East Africa
by Hedberg (1961).
2. Owing to relaively lower temperatures in
the East Usambara, equivalent forests are
at higher altitudes elsewhere in Africa.
The term 'lowland forest' to cover forest
in the Easten Arc up to 1200 m means
that when comparing the East Usambara
forest types with those in Uganda the
upper boundary of Ugandan lowland
forest would be at the relaively high
alitude of 1700 m (Hamilton et al.
1989).

the driest types of montane forest (Lovett,
1990b).
6. Distribuion pattens of moist forest tree
species throughout the alitude range of
the forests are similar, indicaing that both
upper and lower alitude forests should be
in the same phytogeographic region. In
the Easten Arc there are strong affiniies
to tropical west and cenral African
forests, and a high degree of endemism.

The coninuous nature of change in the orests
is related to a coninuous change in environmen-
tal variables: temperature, which is a funcion of
altitude and distance from the ocean; and rainfall
which is related to topography and laitudina

l
variaion in rainy seasons. A rigid system of veg-
etaion classificaion cannot be applied, but for
pracical purposes the marked alitudinal variaion
in moist forests needs to be divided into a number
of convenient types. A terminology similar to that
used by Pocs (l976b, c) is used here in which the
forest is divided into upper montane, montane,
submontane, and lowland, with drier and wetter
types. Phytogeographically all the forests are
regarded as Guineo-Congolian, as there is no
disconinuity between higher and lower alitude
forest in either community associaions or dis-
tribuion pattens, and there are srong affiniies
to West and Cenral Africa. The high degree of
endemism and occurrence of a number of species
with disribuions resricted to easten Africa

'

3. Although there are some differences
between northen and southen parts of
the Easten Arc, the similariies and high
degree of species and generic endemism
within it suggest that it is a disinct
florisic unit and should not be divided
into a southen Uluguru-Mulanje and a
northen Usambara-Imatong group.
4. The Afromontane region of White (1983)
is a mixture of temperate elements in
vegetaion above the forest limits and
ropical elements in the forests, and so is
phytogeographically heterogeneous.
Similarly, his Zanzibar-Inhambane region
is a mixture of Zambezian elements in
woodlands and Guineo-Congolian
elements in forests.
5. Moist forest ree communiy associaions
vary coninuously with alitude (Hamilton,
1975; Hamilton et al., 1989; Lovett,
1990b) and there is no jusificaion or
dividing them into upper Afromontane
and lower Zanzibar-lnhambane types.
Change in community associaions with
alitude is very marked, probably
attributable to the high lapse rate, with
almost complete replacement of species
between upper montane and lowland
forests. For pracical purposes it is useful
to divide this moist forest alitudinal
coninuum into a series of types. There is
a disconinuity between moist forest and

'
suggests that easten and westen secions of the
Guineo-Congolian region, with specific centres
of endemism, should be recognised. This follows
the approach of Monod (1957). Vegetaion above
the forest alitudinal limits has diferent phyto-
geographical affiniies and is here called subalpine
and alpine.
Terminology, together with suggested ali-
tudinal and climaic limits, structural character-
isics and a limited synonymy of the forest ypes
recognised in the Easten Arc, is given below.
Data for stem densiies ( dbh diameter at breast

height) and basal areas are approimate and are
derived from Hamilton et al. (1989) and Lovett
(1992).

=