Résumé
Alley cropping systems present tree rows alternating with crop alleys. Tree rows are uncultivated and often present an understory vegetation strip (UVS), whose impacts have been less studied than those of the trees. Spatial variations within UVSs and between UVSs and crop alleys were investigated for vegetation biomass and necromass, soil organic carbon and nutrient contents, microbial biomass and respiration, and macro-invertebrate density, taxonomic diversity and functional community structure. The first 20 cm of soil were sampled in two young alley cropping sites in South-West France with sown UVSs. Tree distance did not influence studied variables within the UVS. Soil organic carbon and available phosphorus contents were significantly higher in the UVS than in the crop alley, but not soil microbial biomass and macro-invertebrate density and diversity, except for woodlice density. Earthworm distribution in ecomorphological categories differed between the UVS and the crop alley. Microbial biomass and macro-invertebrate diversity were significantly reduced 1 m away from the UVS in both sites. It was concluded that these sown UVSs were not strongly impacted by tree proximity, enriched the first 20 cm of soil with organic carbon, and provided a habitat for specific macro-invertebrates, probably due to reduced disturbance and permanent vegetation. However, UVSs could have a negative impact on soil organisms in their vicinity. Further studies on the role of UVS type, field management and seasonal variation are needed to quantify the role of UVSs on soil properties.