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-2.0 Plant diversity in a Central African rain forest: Implications for biodiversity conservation in Cameroon Figure 2.3 CCA ordination graph based on 958 vascular plant species with DBH ≥ 1 cm recorded in 147 plots showing the influence of environmental variables such as rainfall, altitude, distance from the sea, main soil type, drainage and human disturbance on the various vegetation types. Environmental factors with long arrows are more closely correlated in the ordination than those with short arrows and therefore are more important in influencing the vegetation groupings In some areas where degradation is very severe, only few trees are left standing in a secondary vegetation consisting of pioneer woody and herbaceous species such as Chromolaena odorata, Lycopodiella cernua, Nephrolepis bisserata, Selaginella myosurus and S. kraussiana. Marantaceae and Zingiberaceae forests are mainly found along abandoned logging paths. They form thickets of about 2-3 m high and are generally dominated by Marantaceae species such as Haumania danckelmaniana, Marantochloa leucantha, Megaphrynium macrostachyum, Sarcophrynium prionogonium and many species of Aframomum, Renealmia and Costus of the Zingiberaceae and Costaceae families respectively. This vegetation type also supports scattered small and medium sized pioneer tree species such as 30 60 9 59 53 55 54 56 61 126 58 62 10 57 132 131 35 128 136 56 19 34 7 16 18 13 15 12 14 1 11 2 8 20 23 32 48 41 24 22 25 42 33 2643 36 46 44 21 45 34 3839 40 30 37 27 28 29 31 4947 50 65 6766 52 63 51 68 69 7172 64 112 80 78 7 84 76 4 8375 77 79 81 82 92 87 113 119 120 121 114 122 125 127 142 143 144 137 123 135 124 141 140 139 138 129 145 Okoumé -Swamp Mixsemideci 147 146 63 Caesalpcasa 17 Soil type Drainage Disturbance -Cosaca Mixevergreen -1.0 Altitude 0.0 1.0 -Submontane Caesalpsa -0.5 89 1 -1.5 88 CCA Axis 2 Rainfall 9 3 130 Caesalp 98 Distance from the sea 102 85 86 106 103 96 104 91 95 105 101 97 107 115 134 109 118 116 117 108 111 99 100 133 Mangrove 94 110 9 0 CCA Axis 1 -Cosaga -Cosas
Central African tropical rain forest structure and composition Alchornea cordifolia, Anthocleista schweinfurthii, Bridelia micrantha, Harungana madagascariensis, Musanga cecropioides, Trema occidentalis and Macaranga species. This forest association appears to be the main habitat for forest elephant, buffalo, gorilla, chimpanzee and many other large primates because of its good cover and high food production. DCA and CCA analyses The species-environment biplot from the CCA analysis is presented in Figure 2.3. As shown in Table 2.2, the first two axes of the DCA and CCA analyses of the data set have eigenvalues above 0.5, which denotes a good separation of the species along these axes despite a low amount of species variance explained. TWINSPAN and correspondence analyses have produced a similar classification since most of the plots that were found together in the various TWINSPAN groups were also put together in the CCA classification groups. Table 2.2 Summary table of DCA and CCA of 147 plots recorded in the Campo-Ma'an area. Axis 1 Axis 2 Axis 3 Total inertia DCA 20.83 Eigenvalues 0.92 0.74 0.66 Lengths of gradient 9.38 4.35 4.71 Cumulative percentage variance of species data 17.26 4.75 4.73 CCA 20.83 Eigenvalues 0.68 0.61 0.54 Species-environment correlation (Pearson correlation) 0.97 0.95 0.95 Cumulative percentage variance of species data 3.4 6.2 8.8 Table 2.3. CCA canonical coefficients of 10 important environmental variables recorded in 147 plots distributed over the Campo-Ma’an area. Environmental factors Axis 1 Axis 2 Axis 3 Mean annual rainfall (mm.y-¹) 0.13 -0.60 -0.21 Altitude (m above sea level) -0.76 0.38 -0.12 Distance from the sea (km) -0.01 -0.62 -0.14 Disturbance 0.34 0.10 0.09 Soil characteristics Main soil type 0.07 0.02 -0.36 Parent material -0.03 -0.10 -0.09 Drainage 0.07 -0.03 -0.61 Top soil texture (0-10 cm) -0.06 -0.02 -0.04 PH (H20) of the top soil (0-10 cm) -0.04 -0.09 -0.11 Electricity conductivity of top soil (0-10 cm) 0.03 -0.01 0.10 Environmental factors such as rainfall, proximity to the sea and altitude are more closely correlated with the vegetation ordination than soil characteristics. Almost all the coastal plots (Cosaca, Cosaga and Cosas), mangrove, swamps and lowland evergreen forest rich in Caesalpinioideae (Caesalp, Caesalpcasa and Caesalpsa) are negatively correlated with altitude and positively with increasing rainfall. Plots that were located in the rain shadow in the Ma’an area (Mixevergreen and Mixsemideci) are characterised by a lower rainfall. The effect of altitude is also well illustrated by 31
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Plant diversity in a Central Africa
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Chapter 5 BIODIVERSITY HOTSPOTS AND
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Chapter 6 GENERAL CONCLUSIONS AND I
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REFERENCES
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ANNEXES
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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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