Earthworms and agricultural systems: Status of knowledge and research in Canada

Since the ratification of the United Nations Convention on Biological Diversity, there has been increased interest in issues related to biodiversity, particularly with respect to soil biodiversity and the influence of agricultural practices. This paper is one of a series of papers contributing to a state of the art review initiated by Agriculture and Agri-Food Canada on the status of soil biodiversity research in Canada, particularly with respect to agroecosystems. The objectives of this paper are to provide an overview of earthworm species distribution in Canada by province and territory, and to review research that illuminates our understanding of the ecological relationships of earthworms in agricultural systems. Most Canadian earthworm species are considered exotics having generally been dependent on human activity for their introduction and dispersal throughout the Canadian landscape. Twenty-seven earthworm species have been identified so far in Canada; of these, eight species are native to North America. Suggestions for future research on earthworm biodiversity within an agricultural context are discussed including: the need for increased spatial and temporal information on earthworm distributions across Canada, particularly with respect to Canadaʹs varied agroecosystems and landscapes; information on the ecology of earthworms with respect to their contributions to the soil system and their interactions with other soil fauna; the need for ecosystem process models relating earthworm contributions to soil structure formation and transport of materials and nutrients within the soil system; and the need to determine threshold levels of earthworm species associations in order to optimise effectively their contributions to soil quality and plant growth. To facilitate these studies, expansion of taxonomic expertise and capability across Canada will be required.