A quantitative synthesis of earthworm effects on plant litter decomposition and SOC was undertaken based on 340 observations from 69 independent studies. A positive correlation between earthworm density and the rate of plant litter decay was found, and that the presence of earthworms doubled the amount of litter mass loss on average. The presence of all three (anecic, epigeic and endogeic) earthworm functional groups was associated with higher litter mass loss than when either one or two functional groups were present. Anecic earthworms had the strongest effect on litter mass loss, followed by epigeic earthworms, and there was no apparent influence by endogeic worms.
The resutls of this study indicate that the effect of earthworms on litter and soil organic carbon (SOC) decay depends strongly on earthworm functional groups and diversity, and that a high diversity of earthworm functional groups accelerates litter mass loss and SOC decay. Thus, changes in land management practices are likely to alter ecosystem carbon cycling through alteration of earthworm abundance and diversity.