Les Forêts Sacrées Dans Les Hautes Terres De l’OuestCameroun : Intérêt Dans La Conservation De La Biodiversité

La végétation des Hauts plateaux de l’Ouest-Cameroun est pratiquement domestiquée, les espèces originales sont réfugiées dans des reliques de forêts, dans des zones à accès difficile dans des forêts ripicoles le long des cours d’eau ou dans des forêts dites forêt sacrées. Le présent travail vise à évaluer la diversité floristique et à faire une analyse qualitative et quantitative de la flore de quelques forêts sacrées dans l’Ouest du Cameroun. Le statut de conservation des espèces a été également déterminé. Le recensement des individus s’est fait dans 41 placettes de 25 m x 25 m établies dans les forêts sacrées de Bafou, Baleveng, Bamendou, Mbing Mekoup, Bamendjinda et de Bamendjo. Le nombre de placettes par forêt dépendait de la taille de la forêt. À l’intérieur de chaque placette, tous les individus de diamètre supérieur ou égal à 10 cm à hauteur de poitrine (1,30 m) ont été considérés. Les indices de diversité de Shannon et de Simpson ont été utilisés pour évaluer la phytodiversité ; les valeurs d’importance des espèces et des familles ont été calculées. Le test d’ANOVA a été utilisé pour comparer statistiquement les données. Globalement, 2 829 individus de diamètre ≥ 10 cm appartenant à 91 espèces, 85 genres et 47 familles ont été inventoriés. Les valeurs des indices de diversité sont faibles (de 0,73 et 2,49 bits par placette pour l’indice de Shannon ; de 0,02 à 0,89 par placette pour l’indice de Simpson). Elles traduisent la faible diversité floristique de la zone. La surface terrière varie de 14,44 m2.ha-1 à 65,6 m2. ha-1 par forêt. L’analyse factorielle des correspondances individualise la flore en trois grands groupes suivant un gradient topographique, hydrologique et anthropique. La classification ascendante hiérarchique confirme les résultats de l’analyse factorielle des correspondances en individualisant trois grandes classes de flore. Le facteur altitude semble être le facteur principal qui influence l’individualisation de ces groupes déterminés par les analyses multivariées. D’après la liste rouge des espèces menacées de l'Union Internationale pour la Conservation de la Nature ; six espèces du total enregistré sont en situation de vulnérabilité (Prunus africana, Podocarpus mannii, Entandrophragma utile, Entandrophragma candollei, Cordia platythyrsa, Antidesma venosium). Cette étude souligne l’importance de la flore des forêts sacrées, les données obtenues pourront servir de bases pour une gestion durable de ces forêts. The vegetation of the Western Highlands is almost domesticated, and the original species are found in forest relics called sacred forest. These sacred forests also have an important number of floristic species. This work aims to assess the floristic diversity and to make a qualitative and quantitative analysis of the flora of some sacred forests in West Cameroon. The conservation status of the species was also determined using IUCN redlist. The census of individuals was carried out on 41 plots of 25 m x 25 m established in the selected forests. The number of plots per forest depended on the size of the forest. Within each plot, all individuals with a diameter greater or equal to 10 cm at breast height (1.30 m) were considered. The Shannon and Simpson diversity index were used to assess phytodiversity; importance values for species and families were calculated. The ANOVA test was used to compare the data. Overall, 2829 individuals with a diameter of ≥ 10 cm belonging to 91 species, 85 genera and 47 families were inventoried. Diversity index values are low (0.73 and 2.49 bits per plot for the Shannon index; 0.02 to 0.89 bits per plot for the Simpson index). These reflect the low floristic diversity of the area. The basal area varies from 14,44 m2. ha-1 to 65.6 m2. ha-1 per zone. Correspondence factor analysis individualizes the flora into three major groups following a topographic, hydrological, and anthropogenic gradient. Clustering hierarchical analysis confirms the results of the AFC by grouping the flora into three main classes according to the altitude. Amongst the species recorded, six others are in a vulnerable situation (Prunus africana, Podocarpus mannii, Entandrophragma utile, Entandrophragma candollei, Cordia platythyrsa, Antidesma venosium). This study highlights the importance of sacred forest vegetation as a basis for sustainable management of these forests

Expériences sylvicoles au Cameroun : Croissance, mortalité et adaptabilité des espèces de bois d’oeuvre dans la station forestière de Mangombé (1964 - 2010)

Au Cameroun, l’exploitation du bois a entraîné la réduction du couvert forestier et son appauvrissement en espèces de bois d’oeuvre. Pour remédier à cette situation, de nombreuses plantations forestières ont été crées, puis abandonnées quelques décennies plus tard pour des raisons diverses, ce qui n’a pas permis de capitaliser l’ensemble des connaissances sylvicoles escomptées qui devaient permettre de réhabiliter les forêts et limiter les risques d’épuisement des stocks d’essences commerciales. Le dispositif sylvicole de Mangombé fait partie de ces initiatives, il ne compte plus que 27 parcelles d’arbres constituées de 15 espèces sur une quarantaine plantées. Ce travail, présente l’état de cette station forestière à travers l’étude de la croissance, de la mortalité des arbres et de l’adaptabilité des espèces. Dans chaque parcelle, toutes les tiges ont été inventoriées et leur diamètre à 1,30 m mesurés. Ce paramètre a permis d’établir la structure de population et d’apprécier la possible rentabilité économique des espèces. Les meilleures performances de croissance des arbres sont obtenues chez Gmelina arborea Roxb. (Gme-1 : 56 m²/ha) ; Araucaria cunninghamii Aiton ex D. Don (Ara-1 : 63 m²/ha) et Aucoumea klaineana Pierre (Auc-3 : 80 m²/ha). Les valeurs élevées des écarts types indiquent une croissance disproportionnée des individus à l’intérieur des parcelles. Les espèces présentant une faible mortalité et une proportion importante de tiges exploitées ainsi que de bonnes caractéristiques de croissance comme G. arborea, Dipterocarpus alatus Roxb. ex G. Don. (51 m²/ha) et A. klaineana se sont mieux adaptées au site de plantation et peuvent être recommandées pour les initiatives de reboisement dans la zone. La faible production observée chez un nombre élevé d’espèces est économiquement non rentable au regard des investissements onéreux consentis à la mise en place de la plantation.© 2015 International Formulae Group. All rights reserved.Mots clés: Mangombé, Cameroun, plantation forestière, sylviculture, croissance des arbres, mortalité, adaptabilitéEnglish Title: Sylvicultural experience in Cameroon: Growth, mortality and adaptability of wood species in Mangombe forest plantation (1964 - 2010)English AbstractIn Cameroon, logging has led to a reduction in forest cover and an impoverishment of several wood species. To solve this problem, many forest plantations had been created, then abandoned a few decades later for various reasons. This did not make it possible for foresters and policy makers to acquire expected knowledge from these experiences, which would have led to forest rehabilitation and reduced the risk of commercial wood extinction. Mangombe tree plantation is part of these experiences, which is a remnant of 15 out of 40 originally planted tree species distributed in 27 plots. This work presents the state of Mangombe forest plantation through the study of the growth, mortality of the trees and adaptability of species. All the trees were censored and their diameters measured in each plot. These measurements facilitate the establishment of the population structure and appreciate the economic profitability of the species. The best growth performances of trees were obtained with Gmelina arborea Roxb. (Gme-1 : 56 m²/ha) ; Araucaria cunninghamii Aiton ex D. Don (Ara-1 : 63 m²/ha) and Aucoumea klaineana Pierre (Auc-3 : 80 m²/ha). High values of standard deviations indicate a disproportionate growth of the individuals inside the plot. Species presenting a low mortality and a significant proportion of exploited stems as well as good growth characteristics such as G. arborea, Dipterocarpus alatus Roxb. ex G. Gift. (51 m²/ha) and A. klaineana were better adapted to the site and can be recommended for future initiatives of afforestation in the zone. The low production of certain species is economically non profitable considering the high investment during the establishment of the plantation.© 2015 International Formulae Group. All rights reserved.Keywords: Mangombé, Cameroon, forest plantation, sylviculture, trees growth, mortality, adaptabilit

Assessment of Fuel Wood Values and the Influence of Wood Cutting on the Easily Flooded Plain Woodland of the Sahelian Area, Cameroon

The study focused on fuel wood economic value and the influences of woody cutting on woody species in the flooded plains woodland area. Sahelian woodland suffers from cutting down trees for fuel wood, to insure household energy demands. Investigations were carried out near a sample of users of resources and an inventory of stems of exploited species in woodland. Households in 15 villages and four markets were explored and 496 actors included in the exploitation and the use of firewood and charcoal, as regard 204 men and 292 women, were interviewed individually. Fuel wood quantity and economic value was made through a register. Through 48 transects of 2 000 m length and 20 m each, the availability, the intensity of cutting down trees, measurements and observations were made and noted on stems. Stems which the circumference > 10 cm were counted and their diameter was measured. The sources of domestic energy mostly used were firewood and charcoal which remained easily accessible and available. Completely stem cut down and partial stems cut were noted as the exploitation mode. The charcoal was produced traditionally, using furnace. Significant quantity of firewood (2186.59 t) and charcoal (28340 t) were estimated. It varied periodically a year with a substantial drop. The quantity sale represent 95 % and brought annual income of 122035.8 $(Firewood) and 31 630$ (charcoal). The incomes contributed significantly in the rural households’ economy and brought an additive to their much reduced agricultural yields. A number of 33 woody species were noted as the mostly exploited for fuel wood. Among them Anogeissus leiocarpus, Balanites aegyptiaca, Prosopis Africana, Detarium microcarpum and Pseudocedrela kotschyi were firstly mention. The total number of stumps and the partial cut of stems were significant representing respectively 20.91 % and 9.64 % of stems counted. The exploitation was intensive and selective on stems. Cutting down of stems was constituted a major factor for requested species degradation. Results indicated evidence of the impacts of fuel wood exploitation on the woody species. The study concludes that fuel wood yield in the sahelian woodland has not yet reached alarming proportions and can be contained. It could be an imperative to set up an alternative system to ensure sustainable management of resources. Solutions through introduction and popularization of natural gas, biogas, solar energy and the improved hearths could effectively contribute to reduce the intensity of this activity and to guarantee the maintenance of the ecological balance on the already fragile sahelian ecosystems

Variabilité Structurale Des Peuplements D’arbres En Forêt De Montagne Du Parc National De Kahuzi-Biega Et Ses Environs, RD. Congo

This work aims to determine the change in the diametric structure, density, basal area, height and dominance of trees dbh ≥ 10 cm depending on altitude range or forest types. The study was conducted in 30 ha in Kahuzi Biega National Park and surrounding areas in DR Congo. In total, 16,797 individual trees were surveyed. The number of family, genus and species regress following the altitudinal gradient as the density increases. Mountain ecosystems in Kahuzi-Biega and its surroundings are dominated by Meliaceae, Euphorbiaceae, Moraceae, Fabaceae and Rubiaceae families. The Chi square analysis showed that the diametric structure of vegetation succession following a progressive dynamic and varies according to altitude gradient. The average basal area was 35 m²/ha. The analysis of variance (ANOVA) and post hoc Tukey test does not prove the impact of altitude on the basal area. But it becomes low in elevation due to the reduced diameter of the trees. The vertical structure was analyzed according to the classification IUFRO (International Union of Forest Research Organizations). The maximum height was 48 m and becomes lower in altitude. The tree height diameter relationship varies according altitude range so that the models H/D in this area should be developed for each forest type. We determine that the dominance of woody species following the altitude effect; only Strombosia scheffleri and Xymalos monospora dominated by its basal area, abundance and frequency of the various altitude horizons

Can the Mangombe forest plantation contribute to restore and conserve biodiversity?

This research, conducted in the tropical rainforest, is focused on restoration of tree diversity through natural regeneration mechanism in the 49 year-old Mangombe forest plantation. 12 plots were surveyed, 6 with large transects and the 6 others under regrowth. In each plot, two subplots with 400 m² each were demarcated for the inventory of all stems with diameter greater than 2.5 cm. A total of 2239 stems comprising 107 species distributed in 93 genera and 42 families were identified over 9600 m². There was a slight difference between species richness of plots with large transect (79 species, 72 genera and 35 families) and regrowth plots (85 species, 76 genera and 38 families) while the basal area in the plots with large transects (10.76 m²/ha) was significantly greater than that of regrowth (8.65 m²/ha). Species with high important value index have an affinity with forest undergrowth such as: Tabernaemontana pachysiphon, T. crassa, Mallotus oppositifolius and Heinsia crinita. The undergrowth is diversified with different life feature and a high number of small size trees indicating a vigorous regeneration. This can be favoured by: microclimate undergrowth, canopy gaps, abundance of litter fall that brings humus to the soil, type and age of plots, planted species and the complexity of spatial and vertical structure of the stand.© 2016 International Formulae Group. All rights reserved.Keywords: Mangombé – Cameroon, Natural regeneration, dense humid forest, tree plantation, biodiversit

Caractérisations Structurale, Floristique Et Biomasse Ligneuse Du Peuplement À Hagenia abyssinica Du Parc National De Kahuzi-Biega (Rift Albertin, RDC)

Hagenia abyssinica is a characteristic species of mountain forests in the Albertine Rift. In Kahuzi Biega National Park, the species is found between 2000 and 2600 m altitude. This study intended to characterize Hagenia monospecific forest by providing an account for its floristic composition, structure and biomass. Data were collected from 9 different plots of 1 hectare each located in 3 different sites (Tshivanga 2000-2250m asl; Mugabe and Kasirusiru 2400-2600m asl). Parameters including tree diameter ≥ 10cm, height, dead individuals and young shoots of Hagenia abyssinica were wetting the plot. The results showed that species richness was significantly low, varying between 8-24 species (p < 0.05, Df = 35); while the specific density was 565 ± 121 individuals. The Richness decreased with the increment of the species density of Hagenia. The similarity analysis revealed the influence/impact of the site/altitude on the species composition. The diametric structure showed a regressive dynamism within the population found between 2000 and 2200 m altitude, in which Hagenia specimens were replaced by the specimens of secondary forest species such as Sapium ellipticum, Macaranga neomilbraediana, Neoboutonia macrocalyx. Whereas, between 2400-2600 m altitude, there was a progressive dynamism with several Hagenia young shoots, with no mortality (χ2 = 487, p < 0.001). The average woody biomass was estimated at 108t / ha. This increased as Hagenia density decreased and vegetation became heterogeneous. Human disturbance and climate change effects in the region, could be the causes of variability observed in this population in the Kahuzi-Biega National Park

Diversité Floristique Et Structurale De Deux Forêts Communautaires Sous Exploitation Au Cameroun: Cas De Kompia Et Nkolenyeng

The attribution of community forests to local populations has emerged as a new participative management system of plant biodiversity in Cameroon. Further to the intensification of anthropogenic activities in these forests, the logging impact on this biodiversity remains poorly known. This study was conducted in two different community forests located in the Kompia and Nkolenyeng villages, respectively. It aims to provide information on the state of the flora and plant structure of the community forests subjected to logging activities. Floristic inventories were carried out in nine biotope types using the variable-area sampling method. A total of 2772 individuals with dbh ≥ 10 cm were recorded in the community forests. In the whole biotopes, the species richness ranges from 19 to 98 species, the Shannon diversity index from 3.63 to 5.99 and the Pielou evenness from 0.65 to 0.93. The density of trees ranges from 73 ± 27 to 661 ± 119 stems ha-1 , the basal area from 15.68 ± 13.14 to 70.05 ± 28.76 m² ha-1 , the mean diameter of 18.85 ± 4.80 to 57.39 ± 20.70 cm and the canopy height from 12.26 ± 1.22 to 25.18 ± 1.02 m, on the average between biotopes. The two community forests showed decrease in tree density, a proliferation of the pioneer species, increase of small-diameter light-demanding species, a scarcity of large-diameter trees, and lowering of canopy height. These changes could compromise the sustainable management of these forests and their ability to ensure long-term local development. The large number of useful species identified in the two community forests is a reason to reinforce the preservation and management measures of the plant biodiversity of these forest areas

Height-diameter allometry and above ground biomass in tropical montane forests: Insights from the Albertine Rift in Africa

Tropical montane forests provide an important natural laboratory to test ecological theory. While it is well-known that some aspects of forest structure change with altitude, little is known on the effects of altitude on above ground biomass (AGB), particularly with regard to changing height-diameter allometry. To address this we investigate (1) the effects of altitude on height-diameter allometry, (2) how different height-diameter allometric models affect above ground biomass estimates; and (3) how other forest structural, taxonomic and environmental attributes affect above ground biomass using 30 permanent sample plots (1-ha; all trees ≥ 10 cm diameter measured) established between 1250 and 2600 m asl in Kahuzi Biega National Park in eastern Democratic Republic of Congo. Forest structure and species composition differed with increasing altitude, with four forest types identified. Different height-diameter allometric models performed better with the different forest types, as trees got smaller with increasing altitude. Above ground biomass ranged from 168 to 290 Mg ha-1, but there were no significant differences in AGB between forests types, as tree size decreased but stem density increased with increasing altitude. Forest structure had greater effects on above ground biomass than forest diversity. Soil attributes (K and acidity, pH) also significantly affected above ground biomass. Results show how forest structural, taxonomic and environmental attributes affect above ground biomass in African tropical montane forests. They particularly highlight that the use of regional height-diameter models introduces significant biases in above ground biomass estimates, and that different height-diameter models might be preferred for different forest types, and these should be considered in future studies