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Despite the importance of forests and trees, Senegal is facing to the loss of forests and the decline of tree diversity and density. This study focuses on Moringa oleifera Lam., Acacia mellifera (Vahl) Benth. and Zizyphus mauritiana Lam. which constitute a significant source of food and economic value for the populations of Casamance.In addition to a germination test, a follow-up of seedlings on different substrates was carried out in the nursery, in order to determine the effect of substrates on some growth parameters (number of leaves, height, diameter and biomass).The substrates used were three potting mixtures of forest soil of Faidherbia albida (FSFA), Elaeis guineensis (FSEG) and Anacardium occidentale (FSAO) and sand with the following proportion: 1/3 sand + 2/3 forest soil). Based on species, the germination rate was higher for A. mellifera (84%) followed by M.oleifera (55%) and Z. mauritiana (50%). The germination rate was more important in FSFA and FSEG than in FSAO. For growth parameters, there was a significant effect (P<0.05) of substrate type on height, diameter, number of leaves and root biomass. In term of growth parameters, the seedling performed better in FSFA and FSEG than in FSAO. The species effect was also significant (P<0.05) with higher root biomass and diameter found in M. oleifera and height and number of leaves in A. mellifera. The most important total biomass was found in FSFA followed by FSEG. Comparing the fraction of biomass according to the part of the seedling, the stem and branch had the higher fraction of biomass for A. mellifera (43%) and M. oleifera (38%) and the leaves for Z. mauritiana (46%).However, thetype of substrate can affect seedling development and growth parameters and the better results were recorded in FSFA and FSEG substrates.

In Senegal, in the Sahel region, the agroecosystem is dominated by two Sahelian shrubs able to redistribute water from deep soil to the surface. This study was carried out to determine the impact of these shrubs on soil microbial activity. A 2 × 3 factorial design was set up during the dry and wet season with three soil treatments: rhizospheric, bulk and non-rhizospheric soil. During the dry season, the presence of shrubs resulted in significantly higher phosphatase acid activity for Guiera senegalensis (p < 0.001), respectively, 717 µg pNP/h/g of dry soil in the rhizosphere soil, 333 µg pNP/h/g in the bulk soil and 193 µg pNP/h/g in the non-rhizosphere soil. The same trend was observed for all other enzyme activities and MBC during both seasons except for mineral N. Mineral N was not statistically different between the rhizospheric and bulk soil during the dry season. β-glucosidase and phosphatase acid had the highest correlation with the rhizospheric soil during the dry season respectively 98% and 97%. Soil moisture content was highly correlated with the rhizospheric soil (85%), chitinase activity (99%) and β-glucosidase (97%).Shrubs maintained a moister environment during the dry season which was critical in stimulating microbial activities; this has significant implications for agroecosystem management in the Sahel.