Efectos de varias epecies de arboles sobre el estrato herbaceo y la dinamica del nitrogeno del suelo en la zona Sudaniana de Camerun

During five years of fallow on a site in the North of Cameroon, protection against grazing with or without the introduction of tree species (Acacia polyacantha, Senna siamea and Eucalyptus camaldulensis) induced a progressive evolution to a particular herbaceous species composition in each treatment. Herbaceous grass biomass was at least 50% lower below the tree canopy than in full sun. In a natural fallow protected against grazing (no trees), the cumulative production of Andropogon gayanus provided the greatest biomass (8 t ha-1 after five years). E. camaldulensis provided little shade, allowing the growth of A. gayanus, and thus herbaceous biomass (3.5 t ha-1) was higher in this treatment than under the other tree species. The herbaceous strata below A. polyacantha (2.24 t ha-1) had the greatest N concentration (up to 13%) due to N fixation and a high soil N mineralization. S. siamea had a strong depressive effect on soil N mineralization and on the biomass of the herbaceous stratum. (Résumé d'auteur