Résumé
This study was carried out to describe the driving factors responsible for earthworm community structure in a wet landscape of the Seine Valley (Upper Normandy, France). Fifteen plots were selected along a 1300 m transect, representing the main agroecosystems (i.e. wooded systems, orchards, grasslands, crops) and soil types (i.e. Fluviosol, Reductisol, Histosol and Colluviosol) in the area. Five samples were taken in each plot using a combination of formalin extraction and hand sorting. Earthworms were identified to species level, counted and weighed.
Communities responded markedly to agricultural intensification. The highest mean biomass, density and diversity were observed in the medium intensity systems (up to 119.7 g fresh weight m
–2, 309.3 ind m
–2, 7.2 sp m
–2 in orchards, respectively). Soil type only had significant effects on community composition and diversity. A principal component analysis was performed with broad descriptive parameters of communities. The first two axes accounted for 50.8% of the total inertia. It separated wooded systems (endogeics and epigeics dominant, low total density, biomass and diversity) from orchards and grasslands (endogeics and/or anecics dominant, high diversity and density) and crops (low diversity, biomass and density). The ordination of plots according to soil type segregated low-lying soils (endogeics and epigeics dominant, low diversity, high density) from better-drained soils (anecics dominant, high density and diversity).
Agricultural activities and natural soil heterogeneity are environmental filters that shape community composition and structure at the landscape scale. In the present study, soil type mainly determined earthworm community composition at the scale of soil type patches, while agricultural practices had a stronger impact on community structure at the scale of the agricultural plot.