Dans le but de gérer durablement les essences forestières du Bassin du Congo où il est noté une insuffisance des connaissances biologiques et écologiques sur la plupart des essences, une étude sur les paramètres de structure et l’état phénologique de Triplochiton scleroxylon K. Schum. (Ayous) et la diversité spécifique des essences accompagnatrices a été entreprise dans le Sud-Est Cameroun. Un inventaire floristique a permis de compter tous les individus de T. scleroxylon et des essences accompagnatrices ayant un diamètre à hauteur de poitrine (DHP) supérieur ou égale à 10 cm. Les paramètres de structure ainsi que l’état phénologique ont été observés ou mesurés. La richesse spécifique des essences accompagnatrices dans la parcelle permanente et sur le parcours phénologique se compose de 46 espèces réparties dans 20 familles et 39 genres. L’indice de diversité de Shannon-Weaver (4,61) et celui de l’Equitabilité de Piélou (0,83) sont élevés dans la parcelle étudiée comme dans l’ensemble des forêts tropicales. Les DHP des individus de T. scleroxylon varient de 80 à 130 cm avec une moyenne de 110±29,33 cm. La hauteur moyenne du fût est de 14,09 ± 2,55 m. La densité de T. scleroxylon observée dans la parcelle est 11 individus/ha. Ces résultats servent comme des données scientifiques sur la dynamique des individus de T. scleroxylon et des essences forestières accompagnatrices du bassin du Congo.Mots clés : Inventaire floristique, paramètres de structure, état phénologique, diversité spécifique, Triplochiton scleroxylon, bassin du congo.

This study of the impact of heart rot of Pericopsis elata on logging yield was conducted in Libongo, in three logging concessions of the Société d'Exploitation Forestière et Agricole du Cameroun (SEFAC). An inventory of 92 P. elata stumps in four Annual Cutting Areas (AACs) divided among three Forest Management Units (FMUs) distinguished by Minimum Operating Diameter (MOD) revealed that 22 stumps were rotten. Decay was visible on stumps with a diameter of more than 100 cm with a frequency of occurrence of 23.91%, a percentage of abandonment of 55.20% and a yield of 44.79%. The most important economic loss was revealed on 9 abandoned whole logs that cumulated a volume of 145.547 m 3 . The correlation between the diameter of the stumps and that of the decay gives a coefficient or correlation rate r = 0.31.The MOD for P. elata could be 80 cm and covers the biological risk class. The results indicate that P. elata shows an increasing gradient of decay rate with increasing tree diameter, resulting in a loss of material for larger diameter trees, and consequently a decrease in material yield at processing.

The realization of two management inventories in 2003 and 2020 on the same forest concession made it possible to characterize the floristic composition and to describe some structural parameters on three sites established according to the period of exploitation. Due to the change in the orientation of the lines, it was noted that respectively 82 and 85 species from the first inventory are not found in the second and inversely. A total of 311 species were identified in 2003, compared to 314 in 2020. The density varies from 111 to 140 stems/ha for all the individuals, 19 to 25 for the main species and 15 to 20 for the most exploited species. The decrease in the basal area between the two phases of 12% for all the species and 13% for the main species on the site exploited before the first inventory indicates a persistence of the disturbance for years after logging. It is proposed to supplement the management plans decisions with annual measures based on more complete inventories and to ensure the application of reduced impact logging measures.

Influence des sols salins et calcaires sur la croissance, la nutrition minérale et les composantes agronomiques du niébé dans trois zones agro écologiques du Cameroun

The variation of some growth, agronomical and biochemical parameters of Vigna unguiculata (L. Walp) under salinity stress were investigated in the greenhouse and farm conditions. Plants were subjected to 0, 50, 100 and 200 mM NaCl. The increases of NaCl in the culture medium significantly (P< 0.001) decreased the growth parameters (number of leaves, noose diameter, leaf area and stem height), dry biomass (roots, shoots and total), chlorophyll contents and micronutrients (Zn, Fe and Mn) from 100 mM NaCl. Macronutrients (K, Ca and Mg) and K/Na ratio significantly (P < 0.001) decreased in plant partitioning with increasing salinity. The metabolites (proline, total soluble carbohydrates, soluble proteins, total free amino acids, total phenolic and flavonoids contents) significantly (P < 0.001) increased from 50 mM NaCl in variety Ekomcalle compared to Mouala GG and could be considered as biochemical indicators of early selection and osmotic adjustment ability for salt tolerant plants. At 50 mM NaCl, a relative tolerance of variety Ekomcalle compared to Mouala GG for all agronomic parameters (the flowering time, number of flowers per plant, number of pods/plant, number of seeds/pod, pod yield, seed yield and harvest index) was observed suggesting that Ekomcalle could increase cowpeas production on salty soils.