The role of earthworms in grasslands

Grasslands are among the most important ecosystems for human livelihoods. Besides their irreplaceable role in human food production, grasslands provide a wide range of ecosystem services at different scales. Earthworms, being soil ecosystem engineers, can play a key role in affecting the capacity of grassland soils to provide ecosystem services. Earthworms are known to improve soil physical properties, nutrient availability, plant biomass production, and soil water balance. Specifcally, a high earthworm abundance and diversity in grasslands is often related to high soil porosity and water retention, low soil compaction, formation of soil biogenic aggregates with great stability, high availability of nutrients, and accelerated soil organic matter cycling, leading to high plant biomass production. This, in turn, encourages the maintenance of large and diverse earthworm populations in grasslands. Most of the world's managed grasslands sustain livestock production (as opposed to natural grasslands without human intervention). Earthworms are sensitive to agricultural management. For instance, fertilization, grazing and manure management, soil compaction, and modifcation of the plant community composition (i.e., introduction of improved forages, trees, or legumes) can affect earthworm communities in direct and indirect (and often interrelated) ways. Here, we summarize the potential of different grassland management practices and their possible effects on earthworm populations and communities, as well as the subsequent soil properties and functions that underpin sustainable intensifcation. Based on their importance for soil functions and high sensitivity to grassland management, we encourage the inclusion of the earthworm communities among the studied factors for the assessment of grassland management practices' effects on soil health. Furthermore, we suggest that using earthworms as bioindicators of soil health in grassland is practically accessible and easily interpretable by farmers and agriculture services. The development of a standardized method of earthworm assessment, adapted to different edaphoclimatic conditions and types of grassland management, could help to transfer scientifc knowledge generated during the last decades to fnal users and managers of grasslands.