3.3. Vegetation description of the Mwaro corridor
3.3.1. Vegetation structure within the 1-ha plot
The plot established at Mwaro presents distinct stratified
vegetation with all the forest strata well represented. A total of 1246
individuals with a circumference superior or equal to 10 cm has been
inventoried among which trees, shrubs and sub- shrub. Figure 5 schematizes the
stratification of the vegetation of Mwaro as observed from the results of the
1-ha plot.
8 species of which Schrebera alata, Prunus africana, Olea
hochstetteri, Croton macrostachyus, Ehretia cymosa, Bersama abyssinica ssp.
paullinioides, Polyscias fulva and an unknown (Umuhanamambo in the local
dialect, the Kinyabwisha) occupy the superior arborescent stratum (35 - 40 m).
A woody liana Cissus humbertii is found in this stratum.
The middle arborescent stratum is on its part occupied by the
species Albizia adiantifolia., Alangium chinense, Erythrina mildbraedii,
Ekebergia capensis as well as the lianas Gouania longispicata,
Mezoneuron angolense and Mimulopsis solmsii.
In the lower arborescent stratum we find some trees such as
Afrocrania volkensii, Bridelia micrantha, Maesa lanceolata, Tabernaemonta
johnstonii, Drypetes ugandensis and Kigelia africana as well as of the lianas
Urera hypselodendron, Adenia rumicifolia, Rhamnus prinioides, Clerodendron
johnstonii and Toddalia asiatica.
The species, Xymalos monospora, Lepidotrichilia volkensi,
Allophyllus kivuensis, Maytenus arguta constituting the essential of the
sub-wood are at the same time present in the lower arborescent stratum and the
shrubby stratum while Psychotria mahonii, Markhamia lutea, Galliniera
coffeoide. Leptonichia mildbraedii and Oxyanthus speciosus occupy
the shrubby stratum exclusively.
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Figure 5. Structure of the vegetation in the plot at Mwaro (Y
= height in m and X = Plant species)
3.3.2. Dynamic of vegetation prospected in the 1-ha
plot
According to our observations, the phytocenose represented by
the 1-ha permanent plot is an ecotone bearing vegetation of both the average
altitude (sclerophylles forest on stream of lava) and high altitude
vegetation. The evolution of this vegetation seems progressive concidering its
state and the presence of several young plants characteristic to primary
mountain forest such as Strombosia scheffleri, Olea
hochstetteri, Entandrophragma excelsum, Ekebergia campensis, Schrebera
alata and Prunus africana (Figure 5). We also noticed presence of
some individuals belonging to primary forest species, sometimes seen with big
circumferences, but without remarkable promising succession.
Biodiversity survey of Mwaro corridor, Altitudinal
distribution of the vegetation and assessment of Gorilla food
availability
Figure 8. Diameter classes for Bersama abyssinica ssp.
paullinioides
Figure 6. Diameter classes for Olea hochtetteri
Figure 7. Diameter classes for Entandrophragma
excelsum
Figure 9. Diameter classes for Afrocrania volkensi
In Figures 6 and 7 we observe young individuals of Olea
hochstetteri and Entandrophragma excelsum growing in the corridor
and ready to generate a future stable primary forest provided that no external
factors disturb this natural evolution. Observed adult individuals of Olea
hochstetteri are expected to ensure good successors for the maintenance of
this important species. This is similar to the observations of Bersama
abyssinica ssp. paullinioides and Afrocrania volkensii (Figures 8
and 9), two important species typical of Sclerophyles forests growing
on the slope of the northern side of Nyamulagira Mountain on recent lava
streams.
This is not the case for Entandrophragma excelsum,
all individuals of which are young (Figure 7). A long term monitoring
program should be initiated to assess the establishment of this important
species within Mwaro corridor. A similar observation is made for 2 other
species (Ekebergia capensis and Schrebera alata, figures 10
and 11), with the presence of young individuals predicting a good future
representation of a primary forest in the Mwaro corridor, though young
individuals of these two species were limited in number.
Figure 10. Diameter classes for Ekebergia capensis
Figure 11. Diameter classes for Schrebera alata
Figure 12. Diameter classes for Prunus africana
Page 23
Prunus africana (Figure 12) represents a better
distribution of the size classes according to the plot established in the Mwaro
ecological corridor of. Indeed, the tendency of distribution of diameter
classes for this species is a reverse curve in" J ", with a lot of trees of
small size (or young trees) than adult ones. This big number decreases with
regard to the number of individuals of 30 to 60 cm of diameter.
We, however observed, some individuals of very large size
(>60 cm of diameter) that, once extinct will let new generations ensuring a
good conservation status of the species in the Mwaro corridor for long term.
As for Strombosia scheffleri, the recorded
individuals were less than 10 cm in diameter or were seedlings met in the
herbaceous stratum. With time, these individuals will grow up in classes of
diameter = 10 and with the dynamics of the aforesaid vegetation will be part of
the climax forest the environment conditions allow.
Biodiversity survey of Mwaro corridor, Altitudinal
distribution of the vegetation and assessment of Gorilla food
availability
Figure 13. Description of different vegetation types along
the permanent line transect
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