The sound of restored soil: using ecoacoustics to measure soil biodiversity in a temperate forest restoration context

Abstract

Forest restoration requires monitoring to assess above‐ and belowground communities, which is challenging due to practical and resource limitations. Ecological acoustic survey methods––also known as “ecoacoustics”––are increasingly available and provide a rapid, effective, and non‐intrusive means of monitoring biodiversity. Aboveground ecoacoustics is widespread, but soil ecoacoustics has yet to be utilized in restoration despite its demonstrable effectiveness at detecting soniferous soil meso‐ and macrofauna. This study applied ecoacoustic tools and indices (Acoustic Complexity Index, Normalized Difference Soundscape Index, and Bioacoustic Index) to measure belowground (and aboveground as secondary) biodiversity in a forest restoration site spanning two age classes. We collected n = 198 belowground acoustic samples and n = 180 aboveground samples from three recently deforested (felled <3 years ago) and three deciduous forest plots undergoing restoration (for the last 30–51 years) across three monthly visits in South Yorkshire, U.K. We used a belowground sampling device and sound‐attenuation chamber to record soil communities and passive acoustic monitoring to record aboveground sounds. We found that restored plot acoustic complexity and diversity were significantly higher than deforested plots in the sound‐attenuation chamber, but there were no inter‐plot differences in in‐situ soil or aboveground samples. We also found that restored plots had a significantly greater high‐frequency to low‐frequency ratio (suggesting higher biophony to anthrophony ratios) for in‐situ and sound chamber soil but no association for aboveground samples. Our results suggest that ecoacoustics has immense potential to monitor belowground biodiversity, adding to the restoration ecologist's toolkit and supporting global ecosystem recovery.