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Plant diversity in a Central African rain forest: Implications for biodiversity conservation in Cameroon Caesalpinioideae were characterised by high GHI scores, low PI scores and low level of disturbance. Other areas of high concentration of strict and narrow endemic species were located outside the park in the coastal zone and in areas such as Mont d’Eléphant and Massif des Mamelles. Unfortunately, these areas that support 17 strict endemic species that are not found in the park were much more affected by human activities. Most forests located at their closed vicinity were characterised by high PI scores with more than 25% of the forest cover affected by recent human disturbance. Overall, the Ma’an forest and the coastal forest on sandy shorelines showed a low concentration of endemic species. Despite the rich biological and scientific importance of the area, the Campo-Ma’an rain forest is seriously affected by human activities such as urbanisation, agriculture and timber exploitation. Cameroon has a population of about 15 millions with a high growth rate of 3.2% (Gartlan, 1992). Furthermore, she is experiencing an economic crisis that has significantly reduced the national budget and employment opportunities, and increased the poverty level of the people. So far, most Cameroonians rely heavily on agriculture and forest resources for subsistence. Therefore, with the growing human population rate, local pressure on these fragile ecosystems will increase in the future. Deforestation for agricultural purposes is the biggest threat to the tropical rain forest since shifting agriculture and permanent plantations increase by about 75,000 to 95,000 ha per year in Cameroon (Gartlan, 1992). In the Campo-Ma’an area, agro-industrial plantation and land clearance for subsistence agriculture have destroyed more than 15% of the natural forest cover. Long before these recent human activities in the Campo-Ma’an rain forests, man has had a marked influence on the coastal vegetation. This has brought several authors to argue that the coastal forests and the mixed evergreen and semi-deciduous forests in the Ma’an area may have undergone a great change in the past that is probably caused by man (Reynaud & Maley, 1994; Oslisly et al., 2001; Maley & Brenac, 1998; Maley, 2001 & 2002). A strong indication of past human disturbance is the frequent occurrence of Alstonia boonei, Ceiba pentandra, Lophira alata, Pycnanthus angolensis and Terminalia superba, which are characteristic of mature secondary forests in some of the forest types recorded. In a large and heterogeneous forest ecosystem such as the Campo-Ma’an rain forest, the selection of the most appropriate methods for the assessment of the forest is always a difficult matter since many questions need to be addressed in order to decide on the best approach to be taken. To be effective, a botanical assessment method that provided both quantitative and qualitative information was used during our study. The quantitative data came from the enumeration of all vascular plants with DBH ≥ 1 cm in small plots of 0.1 ha each that were established throughout the research area. The qualitative information was generated from herbarium specimen data collected in the various vegetation types and habitats encountered, and from several provisional plant species checklists made in the field in each of these vegetation types. This sampling approach led to the collection of information on all growth forms including trees, shrubs, climbers and herbaceous vascular plants that enable us to study the correlation between tree species diversity and the diversity of other growth forms. The results showed that only 22% of the diversity of shrubs and lianas could be explained by the diversity of large and medium sized trees, and less 118
General conclusions and implications for biodiversity conservation than 1% of herb diversity was explained by the tree diversity. The shrub layer was by far the most species rich in the different plots and vegetation types, and was significantly more diverse and species-rich than the tree and herbaceous layers. Moreover, shrubs contributed for 38% of the 114 strict and narrow endemic plant species recorded in the area, herbs (29%), trees (20%) and climbers (11%). These results indicated that in the context of African tropical rain forest, tree species diversity does not tell it all and therefore, it may not be a good indicator for the diversity of shrubs and herbaceous species. Furthermore, this suggests that biodiversity survey based solely on large and medium sized tree species (DBH ≥ 10 cm) is not an adequate method for the assessment of plant diversity because other growth form such as shrubs, climbers and herbs are under-represented. Inventory design based on small plots of 0.1 ha, in which all vascular plants with DBH ≥ 1 cm are recorded, is therefore, a more appropriate sampling method for biodiversity conservation purposes than assessments based solely on large and medium sized tree species. 6.3. IMPLICATIONS FOR BIODIVERSITY CONSERVATION The Campo-Ma’an National Park The study has demonstrated that the park is of great scientific and conservation importance containing about 72% of the 2297 species of vascular plants, ferns and fern allies recorded in the Campo-Ma’an area and more than 70% of the total endemic species. The site’s conservation opportunities include a rich diversity of flora, fauna and habitats amongst which the most characteristic is the endemic lowland evergreen forest rich in Caesalpinioideae with Calpocalyx heitzii and Sacoglottis gabonensis that only occurs in the Campo area. So far the Park is the only land use type in the area with a legal conservation status. It is fully protected by law, and logging, hunting, fishing, mineral exploitation, pastoral industrial, agricultural and forestry activities are forbidden. However, its boundaries have not been marked in the field, the management plan has not yet been produced, protection is weak and the participation of stakeholders in the management process is not operational. Taking into consideration the fact that the park is surrounded by several land-uses, its management needs to be strengthened and coherent with that of other land-use types found in the area. Furthermore, it is of urgent need to demarcate the boundary of the park, reinforce its protection, complete and implement its management plan as soon as possible. Although the park is virtually free from human disturbance, present human influence is by no means negligible since illegal hunting is frequent. To allow effective control of poaching, several logging tracks and footpaths at the vicinity of the park need therefore to be closed, additional control posts should be established and more forest guards appointed. With its tremendous living genetic resources and its conservation status, the park is an ideal place for scientific research. Further research is needed on the Dipikar Island and in areas east of Mvini’s river and Nkoelon to study the forest dynamics in disturbed lowland forest. This study will help to access the rate of forest recovery after logging in terms of plant species richness, forest structure and composition. Such research is needed because a better knowledge of the effect of human disturbance on the forest ecosystem is important for the development of sustainable 119
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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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