Geology Reference
In-Depth Information
1973). Montane mossy orest (Pocs,
1976c). Upper montane forest (Pocs,
1976b). Wetter ypes of undifereniated
Afromontane forest (White, 1983).
Afromontane bamboo (White, 1983).
Subalpine elfin forest (Pocs, 1976c;
included in Afromontane evergreen
bushland and thicket by White, 1983).
Canopy height: 10-20 m with emergents to 25
m. Basal area: 30-70 m2/ha. Stem sizes:
Few large rees > 100 cm dbh, most trees
<40 cm dbh. Stem density: 330 stems
> 20 cm dbh/ha.
Easten Arc species such as
Cassipourea gummiflua
occur in upper montane forest whereas in the
north they are found in montane forest. Other
endemics include
Croton dicyophleboes, Cussonia
lukwangulensis, Pittosporum goetzei, Polyscias
stuhlmannii, Syzygium slerphyllum.
The latter two
species occur at lower alitudes in the Taita Hills
(R. B. Faden, personal communicaion).
Other trees include:
Aningeria adoi-fr iedeicii,
Aphloia theomis, Cssipourea malosana, Cypto-
caya liebetiana, Dombya tom'a, Dpetes ger-
rardii, Fialhoa lauriolia, Garcinia volkensii, /lex
mitis, Ochna holstii, Ocotea usambarensis, Olea
capensis, Maesa lanceolata, Maytenus acuminata,
Nuxia congesta, Podocarpus latifolius, Rapanea
melanophloeos, Syzygium coratum
(on wet ridge
tops),
Ticholadus elliptius, Xy malos monospora.
Upper montane forest occurs at higher
alitudes than montane forest, and under a greater
rainfall than dry montane forest. It has a greater
basal area than dry montane forest, contributed by
large rees such as
Ocotea usambarensis
and a
higher stem density. Often growing on exposed
ridge tops it has a lower canopy than montane
forest, and in this habitat can have very high den-
siies of small stems. In areas of frequent mist,
epiphic bryophytes orm thick coats on ree
trunks and branches. Rubiaceae, Acanthaceae
and tree ferns are common in the shrub layer. In
areas with suficient rainfall the upper alitudinal
limit is determined by regular occurrence of frost
or a high degree of exposure on ridge tops. Forest
then gives way to subalpine Ericaceous heath, as
in the West Usambara Mountains, or grassland
with tree clumps as in the southern Uluguru and
northen Uzungwa mountains. The grassland for-
est edge is often maintained by fire.
Bamboo thickets appear to be a successional
stage (Hamilton
&
Perrott, 1981; Lovett, 1990a),
so although they have a disincive physiognomy,
it is more pracical to regard them as a type of
upper montane forest. They also occur in mon-
tane forest (Pocs, 1976b). Another species typical
of an early successional stage is
Macaranga
kilimandscharica.
Differences between the norh-
en and southen Easten Arc are that (i)
Bal-
thasaria schliebenii
and
Sy mphonia globulifera
have
not been recorded from the Uzunwa, and (ii)
Bridelia brideliolia, Te nstromia poypetala
and the
endemic
Allanblackia ulugurensis
have not been
recorded rom the Usambara. In the southen
Montane orest
Alitude: 1200-1800 m. Rainall: > 1200
mm/year.
Synonyms: Montane forest zone (Hedberg,
1951). Moist montane forest
(CCT A/CSA, 1956). Middle alitude
submontane moist forest (White, 1970).
Taller types of montane forest (White,
1970). Lower alitude types of upland rain
forest (Greenway, 1973). Montane
evergreen forest (Pocs, 1976c).
Afromontane rain forest (White, 1983).
Canopy: 25-40 m with emergents to 50 m.
Basal area: 30-120 m2/ha. Stem sizes:
Many large trees > 50 cm dbh with a
relaively high proporion > 100 cm dbh.
Stem density: 250 stems > 20 cm dbh/ha.
Montane forest occurs at a lower alitude than
upper montane forest, and is much taller with
bigger trees though the basal areas are similar
owing to upper montane forest having a higher
stem density. Rubiaceae and Acanthaceae are
common in the shrub layer. With decreasing rain-
fall it grades into dry montane forest. In the
Uzungwa Mountains a longer dry season is
reflected by drier forest species, such as
Albizia
gummera, Aphloia theomis, Zyherella mag-
alismontana
and
Rauvoia cara,
growing with
Search WWH ::
Custom Search