Analyse de la distribution spatiale des Acanthaceae en Afrique Centrale et comparaison avec les théories phytogéographiques de Robyns, White et Ndjele.

Cette étude a pour but d\'analyser les modèles de distribution spatiale des Acanthaceae, récoltées en République Démocratique du Congo, au Rwanda et au Burundi et de comparer leur répartition spatiale avec les systèmes phytogéographiques qui couvrent cette zone. Elle porte sur 9181 échantillons regroupés en 48 genres et 310 espèces. Un système d\'information géographique a été utilisé pour réaliser des cartes de distribution de chaque espèce. La méthode multi variée de classification, appuyée par deux indices de structure spatiale (équitabilité et fragmentation) a permis de stratifier la zone d\'étude afin de permettre une comparaison visuelle avec les systèmes phytogéographiques définis par Robyns, White et Ndjele. On note une large distribution spatiale pour certaines espèces sur l\'ensemble du territoire, alors que d\'autres sont inféodées à certains territoires phytogéographiques bien déterminés. Les savanes situées au Sud de l\'équateur contiennent des sites plus riches en Acanthaceae que celles situées au Nord. Les centres d\'endémisme Guinéo-Congolais, Zambézien et Afromontagnard pourraient être les sources de migration des taxons. Les Acanthaceae suivent relativement bien le système phytogéographique de White et sont utilisables en tant que bioindicatrices afin de rapprocher la distribution spatiale des communautés végétales décrites par ce système.By means of 9181 samples representing 48 genus and 310 species, the spatial distribution models of the Acanthaceae family in Central Africa (Democratic Republic of Congo, Rwanda and Burundi) were analysed. Consequently, a comparison to existing phytogeographic systems for the study region was executed. Spatial distribution maps for each species were created using a geographic information system. Subdivision of the study area was realised using a multivariate classification analysis. Using two indices of spatial pattern (fragmentation, class size evenness), the classification result was compared to the phytogeographic zones defined by Robyns, White and Ndjele. While certain species showed a distribution throughout the study area, the presence of other species was found to be bound to one single phytogeographic territory in particular, or to a restricted number of them. The savannas situated in the southern part of the study area contained more Acanthaceae species than the zones situated north of the equator. The Guineo-Congolian, the Zambezian and the Afromontane centre of endemism are suggested to be the origins of taxon migration. Since it was observed that the spatial pattern of the Acanthaceae species corresponded up a certain extent to the phytogeographic system proposed by White, it can be concluded that the Acanthaceae could be used as bio-indicators to proxy the spatial distribution of plant communities as described by this system. Keywords: phytogeography, spatial analysis, Acanthaceae, Central Africa, district, sector.Sciences & Nature Vol. 5 (2) 2008: pp. 101-11

Étude de la croissance diamétrique de quatre essences de bois d’oeuvre exploitées à l’Est du Cameroun

Objectives: This article examines the diametric growth of 4 commercial species, with poor natural regeneration, exploited in eastern Cameroon. The species are Erythrophleum suaveolens (tali), Mansonia altissima (bété), Pericopsis elata (assaméla) and Triplochiton scleroxylon (ayous). Methodology and results: For this purpose, permanent monitoring growth devices constituted by permanent circuits were installed. After 3 years of annual measurements of the tree diameter, a periodic diametric medium growth of 0.68 cm / year for E. suaveolens, 0.37 cm / year for M. altissima, 0.32 cm / year for P. elata and 0.70 cm / year for T. scleroxylon was obtained. Considering the periodic medium growth of two diameter classes below the minimum diameter for logging, a new replenishment rate for the 4 species was calculated.Conclusion and application of findings:These replenishment rates were compared to the replenishment rate obtained using the diametric growth set by the Cameroonian government. There is an overestimation of the possibilities by the administration for M. altissima and T. scleroxylon and an underestimation of the possibilities in the case of E. suaveolens. For P. elata, the replenishment rate obtained in this study permanent devices is substantially similar to those calculated with the diametric growth proposed by the Cameroonian state. The results of this study will serve as a reference to the sustainable management of species with low diametric growth by raising their minimum logging diameter. For species with low natural regeneration as those considered in this study, silvicultural measures should be proposed.Keywords: commercial timbers; management plan; diametric growth; permanent devices; replenishment rate

Analyse de la distribution des Acanthaceae en Afrique centrale: comparaison avec les théories phytogéographiques de Robyns, White et Ndjele.

peer reviewe