Annual changes in earthworm communities along a gradient of forest disturbance

Annual variation in both earthworm abundance and diversity was studied along a land-use gradient in West-Centre region of Côte d’Ivoire. The aim was to assess the impact of human activities on earthworm abundance and diversity, in order to design sustainable management strategies for agricultural land-use. We mainly checked for an increasing trend in earthworm communities, along a gradient of forest disturbance during the first sampling year (2016). For this reason, earthworm populations were sampled in the following year (2017) during the same period, using similar sampling procedure. Both earthworm density and biomass were 108.0±7.8 ind.m-2 and 21.6±2g.m-2, respectively in 2016. These values were higher than those obtained in 2017, which were 65.4±7.6 ind.m-2 and 10.5±1.1g.m-2, respectively. A similar trend was observed in earthworm diversity. Species richness varied from 5.2±0.2 in 2016 to 3.2±0.2 in 2017, the Shannon index from 1.8±0.0 to 1.2±0.1 and cumulative species from 11 to 12 species. The trend in 2016 was confirmed in 2017, with earthworm abundance and diversity increasing from primary forest to annual crop fields. The fallow systems showed higher abundance and diversity, whereas forest soils had lower values. Between-analyses revealed the prominence of land management impact over the temporal effect. The earthworm species, such as Hyperiodrilus africanus, was the most common in annual crop fields (52.3±12.6 ind.m-2 in 2016 vs 19.2±4.1 ind.m-2 in 2017), making this species a good indicator of disturbed ecosystems.