Ecological preferences of earthworms for land-use types in semi-deciduous forest areas, Ivory Coast

It is widely admitted that earthworms are potential indicators of soil quality. However, very little is known about the preference of species or assemblage of species for a range of ecosystems with respect to soil quality status. This study aimed to find indicator species and species assemblages of earthworms characterizing soil quality measured by soil organic matter (SOM), available P, bulk density (BD) and pH in semi-deciduous forest areas of Ivory Coast. Soil samples along with earthworms were sampled in three sites comprising each one various land-use types (e.g. forests, cocoa plantations, 2 and 5 year-old fallows and mixed-crop fields). Forest conversion into agroecosystems implies marked variations in soil organic carbon, total N, pH and BD, which in turn significantly induced changes in earthworm biomass, species richness and Shannon diversity index. At the end of this study, we came to the conclusion that earthworm species can be used to monitor the status of ecosystems as some species showed preferences to land-use types with different levels of soil quality: (i) Millsonia sp., a geophageous species associated to forests or SOM-rich sites, (ii) Hyperiodrilus africanus, Dichogaster sp.3 and Millsonia omodeoi indicating mixed crop fields or SOM-poor sites, and (iii) Dichogaster eburnea, Dichogaster saliens, Dichogaster baeri, Dichogaster mamillata, Dichogaster terraenigrae, Sthulmannia zielae, and Scolecillus compositus linked to moderately disturbed systems (cocoa plantations and fallows). The contribution of this species or groups of species to monitor soil health is discussed.