Diversité biologique des acariens du sol de la Côte d'Ivoire

In Ivory Coast, CSM-BGBD project (Conservation and Sustainable Management of Below-Ground Biodiversity) aimed to identify the causes of the decline in soil productivity potential and find alternative sites to rehabilitate or preserve. Mesofauna, particularly soil mites play an important role in the ecological functioning of ecosystems. To achieve these objectives, several hypotheses have been listed: (1) abundance, species richness, and diversity were higher for plant formations and ancient undisturbed (2) the abundance ratios between species show a more even distribution when habitat is permanent and unaffected (3) the environmental factors strongly influence the composition of species assemblages (4) the presence of certain species may be indicative of a degree of environmental disturbance. To test these hypotheses, acari soil fauna was sampled in 4 sites with contrasting vegetation physionomy. (Oume primary forest, Tai primary forest, Lamto savanna, Oume teack plantation) and located in two of the three ecological regions of Ivory Coast. The results show that whatever the season, Oume primary forest contains the highest density. Contrary to the hypothesis (1), the lowest density is observed in the Tai forest. Over 50% of the abundance of mites are detected in the upper soil layers. and are more sensitive to seasonal variations than those of deeper layers. The water content and bulk density significantly influence the vertical distribution of soil mites. The species richness of mites sampled is greater in Oume primary forest where habitat is free of human activities. Whereas le lowest species richness was recorded in teak plantation, which is subject to greater disturbance. A low rate of recovery was observed between the study sites. The variation in species richness (beta diversity) is more important between the layers along the transect. The environmental factors (ρapp, Ctot, Ntot, Depth and Corg) are correlated to the richness. The species composition is changed by the water content in the rainy season and is independent of pH. In total 37 species of mites bioindicators of the ecological status of the study sites have been identified. Indicators species of stable habitat (Oume primary forest, Tai primary forest, Lamto savanna) are more abundant than those indicative of disturbed environments (Oume teak plantation). Finally the use of teak plantations as an alternative to the disappearance of natural forests is not strictly allowed given its monospecific character and the many activities taking place therein anthropisation and limit the ecological functioning of soil. In reply it would be advisable to opt for a multi-species reforestation (Source of organic matter more heterogeneous) while limiting the stress factors.