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Plant diversity in a Central African rain forest: Implications for biodiversity conservation in Cameroon Ma’an rain forest lies in the middle of this forest belt which stresses its importance in terms of conservation priorities. In Cameroon, this Biafran forest zone covers about 70,000 km² with three main protected areas that include the Campo-Ma’an National Park, Korup National Park and the Douala-Edea Faunal Reserve. This study, as well as other research (Aubréville, 1968; Letouzey, 1968 & 1985; Reitsma, 1988; Tchouto, 1995; Newbery & Gartlan, 1996; White, 1996; Cable & Cheek, 1998), carried out in this forest zone have shown that in terms of relative abundance, the Caesalpinioideae represent the most important taxon of tree species in the Lower Guinea sub-region, sometimes forming distinctive near mono-dominant stands. However, in the Campo-Ma’an area, several species are co-dominant and many of them are gregarious. Many canopy and emergent trees of the family Leguminosae as well as other tree species such as Desbordesia glaucescens and Terminalia superba have large buttresses and diameters that contributed to the high basal area and forest biomass recorded in the area (Table 6.1). The vegetation in the Campo-Ma’an area is determined by climate especially rainfall, altitude, soils, proximity to the sea and human disturbance (Chapter 1). The structure and composition of the forest, as well as its physiognomy changes progressively as one moves from sea level to 1100 m on hilltops. The vegetation evolves from the mangrove or coastal forest on sandy shorelines through the endemic lowland evergreen forest rich in Caesalpinioideae with Calpocalyx heitzii and Sacoglottis gabonensis, to the submontane forest on hilltops and the mixed evergreen and semi-deciduous forest in the drier Ma’an area. Other vegetation types/sub-types include swamps, seasonally flooded forests, riverine and secondary forests. The forest in the Ma’an area is described as transitional between the coastal evergreen forest and the semi-deciduous forest of the interior. It has a distinct Gabonese affinity with small patches of Aucoumea klaineana (Okoumé) populations that reach their northern limit of distribution around Ebianemeyong on exposed steep hills and Nsengou near to the border with Equatorial Guinea. The strong relation between human disturbance and the vegetation has implications for the floristic composition and species richness of the various forest types. Coastal forests appeared to be more disturbed, including many secondary species, being less species-rich and less diverse than other forest types. 116
General conclusions and implications for biodiversity conservation Table 6.1 Number of species, number of stems/ha, mean basal area/ha and Shannon diversity index (H’) for all vascular plant species with DBH ≥ 10 cm recorded in some forest areas within the Guineo-Congolian region. No of Stems/ha Mean Shannon Notes Authors species basal diversity Inventory site Cameroon area/ha index (H’) Campo-Ma’an (14.7 ha)* 1116 5312 76.71 5.54 Present study Campo-Ma’an (14.7 ha) 532 545 72.9 5.26 2297 species of vascular plants recorded including 30 strictly endemic taxa. Present study Dja Wildlife Reserve (26.14 ha) 372 512 32.6 5.46 Sonke (1998) Korup National Park 410 471 27.8 - Newbery & Gartlan (1996) Korup National Park (50 ha) 307 492 26.7 1.73 Thomas et al., 2003 Korup National Park (50 ha)* 494 6581 32.2 1.93 1100 species Thomas et al., 2003 Mount Cameroon (7.25 ha) 161 444 33.9 3.99 2433 species Tchouto (1995); Cable & Gabon including 49 strictly endemic taxa. Cheek (1998) Doussala (1 ha) 109 425 35.7 - Reitsma (1988) Lope (12.5 ha) 312 389 34.5 - White (1996) Minkébé (3 ha) 202 385 - - van Valkenburg et al., 1998 Oveng (1 ha) 131 497 36.4 - Reitsma (1988) Central African Republic Ngotto forest (2.5 ha) 147 549 34.4 5.3 Lejoly (1995b) Congo Odzala National Park 120 347 21.1 - Lejoly (1995a) Democratic Republic of Congo Cuvette Centrale 206 346 32.3 - Wolter (1993) * for all vascular plant species with DBH ≥ 1 cm Generally, patterns of species richness and endemism are used for the identification of biodiversity hotspots. During our study, inventory data and taxonomic collections were used to assess the distribution patterns of strict and narrow endemic species. Conservation indices such as Genetic Heat Index (GHI) and Pioneer Index (PI) were used to analyse the trends in endemic and rare species recorded and geostatistic techniques helped to evaluate and identify potential areas of high conservation priority. The results showed that the Campo-Ma’an area is characterised by a rich and diverse flora with more than 2297 species of vascular plants, ferns and fern allies belonging to 851 genera and 155 families. The area has about 114 endemic plant species, 29 of that are restricted to the area, 29 also occur in south-western Cameroon and 56 others that also occur in other parts of Cameroon. Furthermore, 540 species recorded are Lower Guinean endemics, 105 species are Guinean endemics and 1123 species are Guineo-Congolian endemics. An explanation for this high incidence of endemism, richness and structured pattern of the vegetation might stem partly from the fact that the area falls within a series of postulated rain forest refuges in Central Africa (Hamilton, 1982; White, 1983; Maley, 1987 &1989; Sosef, 1994 & 1996). In such forest refuges, the unique combination of climatic and geological histories, contemporary ecological variables and inherent biological properties of taxa, may have contributed to speciation (Hawksworth & Kalin- Arroyo, 1995). The distribution patterns of high conservation priority species showed a high concentration of these species in the National Park between Dipikar Island and Ebianemeyong-Akom II area, and on Massif des Mamelles and Mont d”Eléphant. Most of the submontane forest and the lowland evergreen forest rich in 117
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Chapter 1 GENERAL INTRODUCTION Gild
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Plant diversity in a Central Africa
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Chapter 2 CENTRAL AFRICAN TROPICAL
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-2.0 Plant diversity in a Central A
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Chapter 3 DIVERSITY PATTERNS IN THE
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Chapter 4 BIO-INDICATOR SPECIES AND
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SUMMARY Summary The fragile ecosyst
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Summary suggest that the Campo-Ma
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RESUME Résumé La biodiversité de
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Résumé nombreux auteurs qui argum
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SAMENVATTING Gildas Peguy Tchouto M
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