A systematic map of forest disturbance impacts on soil and litter fauna: knowledge gaps and a roadmap for future research

Philip Martin, Leticia Pérez-Izquierdo, Charlotte Biryol, Solene Brasseur, Qian Li, Inti Luna Aviles, Sebastiaan Luyssaert, Bertrand Geunet, Stefano Manzoni, Claire Menival, Catalin Petritan, Rebecca Spake, Mathieu Santonja, Jorge Curiel Yuste

Natural disturbances such as fires, droughts, windthrow, and pest outbreaks are increasing in frequency and severity, placing new pressures on forest ecosystems. Impacts on aboveground biodiversity are well understood, but effects on belowground communities - particularly soil and litter invertebrate fauna - remain understudied. Given the vast diversity of soil organisms, forest types, and disturbance regimes, it is difficult to assess what has and has not been studied, creating major barriers for both new empirical work and meta-analyses. To address this knowledge gap, we conducted a systematic map to characterise global research on the impacts of natural forest disturbances on soil and litter fauna. This identified 308 primary studies, from 48 countries, covering 24 taxonomic orders of soil and litter fauna. We found that most studies focused on fire, while precipitation change, windthrow, and pests/pathogens were underrepresented. By accounting for the area of each forest biome impacted by the different disturbances, we revealed a worrying bias: despite being widely affected by natural disturbances, tropical and boreal forests remain under-studied compared to temperate and Mediterranean regions. We also found that research predominantly focussed on meso- and macrofauna (e.g. springtails and beetles), with relatively few studies on microfauna such as nematodes. For a subset of taxa we compared the number of sites per taxon with global estimates of biomass and found that important groups, such as nematodes, termites, and earthworms are substantially underrepresented. Most studies assessed abundance or alpha diversity, with few studies examining more complex outcomes such as food web structure. Observational designs dominated studies of fire, windthrow, and pests and pathogens while studies of precipitation change often used experimental approaches. Study durations were generally short, and reporting disturbance intensity was inconsistent -  except for precipitation experiments, where it was more common.  Based on our findings, we constructed a roadmap for improving understanding of forest disturbance impacts on soil faunal biodiversity and the essential functions it supports, which we hope will be valuable both for researchers producing primary studies and those conducting meta-analyses.