Data: Nematode-based indices in soil ecology - application, utility and future directions

The underlying data sets contain references from a literature survey that was undertaken using the Web of Science Core Collection database. The data set (Du_Perez_etal_2021_references.ris) contains all references (672) that were used to create the figures in the corresponding paper with the focus on nematode-based bioindicators (NBIs). The data set (Du_Perez_et_al_2021.xlsx) contains all references added by information about NBIs, location information, spatial scale, land use, land cover and study focus which are explained below. We identified three scientific papers, namely Bongers (1990), Ferris et al. (2001), and Ferris (2010), that serve as the foundation and main reference works for scientists and researchers that report on the application of NBIs. In total, 11 NBIs were used in these studies, namely Maturity Index, Maturity Index 2-5, Plant-parasitic Index, Sigma maturity index, Colonizer-Persister (CP) -Triangle, Enrichment Index, Structure Index, Basal Index, Channel Index, Food Web Analysis, and Metabolic footprints. Using the Cited Reference Search tool, a search was conducted for works (up until the end of 2020; last search performed 31 March 2021) that cited each of the above-mentioned scientific papers. This returned 1 113, 653, and 122 citations, respectively, for the Bongers (1990), Ferris et al. (2001), and Ferris (2010) papers. The results were combined, duplicates removed, and further refined to include only peer-reviewed scientific articles. Furthermore, all marine and freshwater studies were excluded. Finally, a total of 1199 papers was included in the analyses. The next step was to screen each paper to assess whether it met the following basic criteria: 1) empirical study (therefore not a review or meta-analysis), 2) application of at least one NBI, and 3) focused on terrestrial habitat(s). A total of 672 scientific papers met these criteria and, from them, the following information was extracted and recorded: i) which NBIs were applied, ii) location information and spatial scale of the study site(s), iii) study focus, and iv) land use and land cover information. The study foci were identified based on the knowledge and experience of the authors. The land use and land cover criteria, in turn, were based on SEEA (2012), which defines land use as ‘the activities undertaken and the institutional arrangements put in place for a given area for the purposes of economic production, or the maintenance and restoration of environmental functions’. Land use therefore classifies all areas under human management according to its use into five categories namely: ‘forestry’, ‘not in use’, ‘agriculture’, ‘built-up and related’, and ‘maintenance and restoration’ . Land cover, in turn, is defined by as ‘the observed physical and biological cover of the Earth’s surface and includes natural vegetation and abiotic (non-living) surfaces’. Six land cover categories were recognized, namely ‘sparse’, ‘grassland’, ‘tree-covered’, ‘shrub-covered’, ‘herbaceous crops’, and ‘woody and multi crop’. The ‘sparse’ category represents both barren terrestrial land and sparsely vegetated land. Further information on each land use and land cover category is provided in the section 3.3. The above mentioned references are as follows: Bongers, T., 1990. The maturity index: an ecological measure of environmental disturbance based on nematode species composition. Oecologia 83, 14-19. and Ferris, H., 2010. Form and function: metabolic footprints of nematodes in the soil food web. European Journal of Soil Biology 46, 97-104. and Ferris, H., Bongers, T., De Goede, R.G.M., 2001. A framework for soil food web diagnostics: extension of the nematode faunal analysis concept. Applied Soil Ecology 18, 13-29. and SEEA, 2012. System of Environmental-Economic Accounting — Central Framework. United Nations, European Union, Food and Agriculture Organization of the United Nations, International Monetary Fund, Organisation for Economic Co-operation and Development, The World Bank, p. 346.