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Plant diversity in a Central African rain forest: Implications for biodiversity conservation in Cameroon
Data analysis
The analysis focussed on family and species level floristic richness and diversity of
the various life forms and forest strata within 145 plots recorded in the area.
Although 11 vegetation types were identified for the Campo-Ma’an area (Chapter
2), the analysis was done on 6 main vegetation types by grouping some of the forest
types for a better illustration of the diversity patterns. All coastal forest types were
grouped as coastal forest, all Caesalpinioideae forests as forest rich in
Caesalpinioideae, the Calpocalyx and Sacoglottis forests as forest rich in Calpocalyx
heitzii and Sacoglottis gabonensis, and the mixed forests as mixed evergreen and
semi-deciduous forest. The 2 plots recorded in mangroves were excluded from the
analysis because mangroves form a mono-dominant community with only 4 species.
In this study tree layer comprised all vascular plant species with DBH ≥ 10 cm,
shrub layer (1.5 cm ≤ DBH < 10 cm) and herbaceous layer (1 cm ≤ DBH < 1.5 cm).
Diversity was measured by recording the number of species (species richness) and
their relative abundance in the different plots and vegetation types. This study
focused on the α diversity (species richness), which is defined as the number of
species within a chosen area, given equal weight on each species, and the β
diversity, which is the difference in species diversity between areas or communities
(Kent & Coker, 1992; Bisby, 1995). β diversity was quantified with the Shannon
diversity index (H’) using all individuals above 1 cm DBH and all species per plot.
Phytosociological parameters (relative density and relative frequency) and Shannon
diversity index were calculated following Whittaker (1975), Kent & Coker (1992)
and Magurran (1988). The SPSS package version 10.0 for Windows was used for
statistical analyses. The Pearson’s correlation test was used to correlate the species
richness and diversity between the various growth forms and forest layers. We
compared the diversity and species richness within forest layers and within growth
forms using a General Linear Model (GLM) followed by a Tukey Multiple
Comparison test (P < 0.05).
3.3. RESULTS
General patterns of species richness and diversity within forest types
A total of 76360 trees, shrubs, climbers and other vascular plants with DBH ≥ 1 cm
was recorded in 145 plots of 0.1 ha each in the various vegetation types. They
belonged to 1112 species, 420 genera and 97 families. In addition, 759 species of
vascular plants (herbs, hemi-epiphytes, shrubs and seedlings of tree species)
belonging to 101 families and 327 genera were recorded in the subplots of 5 m x 5
m each located within the 0.1 ha plots. Overall, 1471 species of vascular plants,
including ferns and fern allies belonging to 542 genera and 126 families were
recorded. More than 73% of all specimens collected were identified at species level,
23% at generic level, 3% at family level and 1% unidentified. As shown in Table
3.1, the number of stems/ha for all vascular plants ≥ 1 cm DBH varied from 5798 in
swamps to 6912 in the submontane forest. The number of species/ha for all vascular
plants ≥ 1 cm recorded varied from 293 in swamps to 468 in the lowland evergreen
forest rich in Caesalpinioideae. The Shannon diversity (H’) varied from 4.73 in
coastal forests to 5.16 in forests rich in Caesalpinioideae. More than 57% of the
plots have above 100 species/0.1 ha and a Shannon diversity (H’) > 4 with the most
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