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Diversity patterns in the flora of the Campo-Ma’an rain forest, Cameroon: do tree species tell it all?
3.1. INTRODUCTION
In a large, heterogeneous and structurally complex forest ecosystem such as the
Campo-Ma’an tropical rain forest, selection of the most appropriate methods for the
assessment of plant biodiversity is a difficult matter. So far, many botanical
biodiversity studies in tropical rain forest are often limited to tree species (mainly
medium and large trees, or for some cases trees with DBH ≥ 10 cm) which are
assumed to reflect the forest floristic composition and physical structure (Letouzey,
1968; Reitsma, 1988; Hart et al., 1989; Mosango, 1990; Koubouana, 1993; Wolter,
1993; Lejoly, 1995a & 1995b; Newbery & Gartlan 1996; White, 1996; Sonké, 1998,
Sonké & Lejoly 1998; van Valkenburg 1998). Moreover, for most of these studies
tree species accounted for more than 50% of the overall species composition. This
traditional approach of forest inventory might not be sufficient for biodiversity
assessment because other taxa such as shrubs, small trees, woody lianas, herbaceous
climbers, herbs and epiphytic flora are not or under-represented. Furthermore, it has
been shown in Central and West Africa that many plant species of high conservation
value such as endemic and rare species are shrub and herbaceous species (Letouzey,
1968 & 1985; Robbrecht, 1996; Sosef, 1996; Achoundong, 2000; Cable & Cheek,
1998). Therefore, assessments based solely on trees might be inadequate for
conservation purposes.
In Chapter 2, we classified, described and mapped the various vegetation types
recorded in the Campo-Ma’an area and analysed the forest structure and
composition. In this Chapter we will study the diversity and distribution of the flora
in the Campo-Ma’an rain forest, and find out whether there is a correlation between
tree species diversity and diversity of other growth forms such as shrubs, herbs and
lianas. This will help us to understand if, in the contest of African tropical rain
forest, tree species diversity tells it all. Are forests that are rich in tree species also
rich in other life forms?
3.2. METHODS
Field sampling
Representative and homogeneous vegetation types were selected on the basis of
physical and human factors such as altitude, slopes, rainfall, soils and land use
(Chapter 2). Sampling was carried out in small plots of 0.1 ha at irregular intervals
along a line transect from a random starting point. In mountainous areas, plots were
located at an altitudinal interval of 200 m along the slope and on both sides of the
ridge. In total 147 plots covering 14.7 ha were established and in each 0.1 ha plot,
all trees, shrubs, herbs and lianas with DBH ≥ 1 cm were measured, recorded and
identified as far as possible. For unknown species, a voucher specimen was
collected. Herbaceous species and seedlings of trees, shrubs and climbers were
sampled in subplots of 5 m x 5 m each that were established in the 0.1 ha plots.
These subplots were not used for the analyses, the output was only used to illustrate
the contribution of the ground layer and herbaceous species when all vascular plant
species are included in the floristic assessment of the forest.
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