Capturing the unseen: a low-cost method for stratifiedsubterranean sampling of soil invertebrates in drylands

Abstract

Drylands cover more than 40% of the earth's land surface and host unique soil meso-and macrofauna vital for ecosystem functioning. Conventional pitfall traps are widelyused to assess surface-active invertebrates. However, they do not adequately samplesubterranean invertebrates, especially in sandy, arid soils. This methodological gaplimits our understanding of the ecological roles of soil fauna in drylands. We aimed to: (i) design a low-cost, stratified subterranean trap for effectively captur-ing macrofauna in dryland soils, (ii) evaluate the sampling method by comparing inver-tebrate diversity and life-stage composition between subterranean traps and pitfalltraps and (iii) assess temporal and spatial variation in richness, abundance and biomasswithin subterranean traps across sampling occasions, macrohabitats and soil depths. We deployed the traps at 10 different transect sites within the three differentland-use types at the study area in the southern Kalahari, South Africa. The trapscaptured invertebrates at multiple depths and in various macrohabitats with twodistinct soil types (white calcareous and red dune sands). Subterranean traps captured taxa and life stages that were not collected in pitfalltraps, including termites (Odontotermes, Microcerotermes), Tenebrionidae larvaeand hypogaeic ants (Dorylus spp.). The taxonomic overlap between the meth-ods was low (12%), with pitfall traps that primarily captured epigaeic ants (79%).Subterranean traps revealed seasonal peaks in taxonomic richness, but therewas no difference in the levels (strata) at which various species were captured.Across macrohabitats, there were differences in taxonomic abundance, withTenebrionidae found more in red dunes compared to white calcareous sands. Practical implication. Subterranean traps are a scalable tool and complementarymethod that improve the ability to monitor and determine soil macrofauna abun-dance and responses to land-use and climate change, offering insights for drylandconservation, diet studies and ecosystem management.