Mgambo Forest Reserve: A biodiversity survey. - Eastern Arc ...

Mgambo Forest Reserve
4.4 Discussion
Mgambo FR covers an area of 13.46 km 2 (1346 ha) with an altitude range of 300m to 800m above
sea level. Topography is, at times, fairly steep but not extreme and the landscape generally a mix
of open woodland, scrub and grassland. Mgambo FR only containted small patches of lowland
forest and riverine forest habitat.
Habitat
Of the 31 vegetation plots surveyed systematically, 20 were open woodland (65% of plots), 5
were lowland forest (16% of plots) and 6 were scrub/grassland/previously disturbed (19% of
plots). Mgambo FR had previously been recorded as 96% poorly stocked lowland forest by
Johannson and Sandy (1996). The large proportion of open woodland actually recorded suggests
increased disturbance in recent years. None of the vegetation plots was recorded with an average
canopy height of over 20m. Approximately two-thirds of vegetation plots had been affected by
fire.
Species richness
In the systematic vegetation plots 858 trees and shrubs were surveyed, representing 101 species
from 31 families. An additional five species were recorded in the regeneration plots. Opportunistic
observations and collections recorded an additional 22 plant species from 14 families. In total 128
plant species from 39 families were recorded.
Relative to other forest reserves surveyed in the East Usambara Mountains the botanical diversity
of Mgambo FR was low, largely as a result of the high level of fire and grazing disturbance.
The most abundant species in vegetation plots, representing 9.0% of individuals was the woodland
species Combretum zeyheri. Other commonly encountered species in vegetation plots were
Dombeya shupangae, Brachystegia spiciformis, Acacia nilotica, Grewia bicolor, Cordia ovalis
and Maytenus undata . All of these species were seen to be resilient to disturbance and at
competetive advantage in disturbed areas.
Endemic Status
The majority of species recorded in vegetation plots (87%) had widespread distributions. Only the
species Cassia abbreviata was recorded as endemic to the Usambara Mountains and 12 species
were recorded as near endemic. The most commonly recorded near-endemic tree species in the
reserve was Dombeya shupangae (55 individuals), then was Scorodophloeus fischeri (15
individuals) and Canthium mombazense (10 individuals). Endemic and near endemic species were
fairly evenly distributed in the reserve, but tended to be more frequently found in the western half
of the reserve.
Only two near endemic species recorded in vegetation plots were forest dependent, namely
Deinbollia kilimandscharica and Zanthoxylum deremense. Three near endemic species, Dombeya
shupangae, Scorodophloeus ficheri and Monodora grandidieri are non-forest species.
East Usambara Conservation Area Management Programme Technical Paper 59
40