Evaluating the restoration potential of transferred topsoil

Global change, population growth and urbanisation are ever-increasing pressures on biodiversity and ecosystem function. Given that conservation of existing natural fragments will not be sufficient to maintain extant biodiversity or meet conservation goals, there is a major need for the practice of ecological restoration whereby degraded lands are managed to increase and maintain indigenous species. However, technical capacity lags and research on restoration tools is vitally needed. One increasingly common restoration tool is topsoil transfer, moving quality topsoil and its associated soil seed bank (SSB), nutrients, and soil fauna to degraded areas. To assess the capacity of topsoil transfer, several key aspects of the SSB were examined parallel to a real-world topsoil transfer in south-west Australia. We evaluated restoration values of topsoil transfer, by investigating plant functional traits, SSB similarity to extant vegetation, exploring mechanisms to improve restoration outcomes, and what influence the process of topsoil transfer has on germinable seed. Glasshouse germination was monitored over 13 weeks from 24 pre and 24 post-transfer soil samples. Treatment included soil depth and smoke plus heat combined. Topsoil transfer resulted in significant seed dilution, equal mixing through the soil profile relative to pre-transfer soils and a marked change in species composition (including lack of perennial species). Smoke and heat failed to stimulate additional germination post-transfer. Topsoil transfer, while successfully translocating native seeds, influences restoration success through dilution and lack of perennial species, thus suggesting a need for topsoil transfer to be supplemented by other restoration techniques, and therefore limiting its cost effectiveness