Incorporating soil biological and functional attributes to advance ecological restoration

Societal Impact Statement: Earth is currently experiencing a mass extinction crisis, predominantly driven by anthropogenic activities, with land use change causing widespread loss and degradation of native ecosystems and indigenous species. There is an urgent need to halt this trend and restore degraded habitat to preserve biodiversity and protect threatened plants and animals. Restoration focuses largely on the vegetation aboveground, with limited attention to soil biology and function, despite soil biodiversity underpinning ecosystem function. We illustrate how soil biological and functional attributes can be implemented to improve restoration outcomes and, under favourable conditions, enhance habitat suitability for threatened plant species. Summary: Anthropogenic activities, including land clearing for agriculture and infrastructure, have resulted in considerable loss of native ecosystems and their unique species. Remnant vegetation is often highly fragmented and degraded, and is under continued pressure from multiple global change drivers. Hence, there is an urgent need to improve remnant vegetation and restore habitat to compensate for these losses. Ecological restoration, however, generally focuses on recovering vegetation structure and composition, with limited attention given to soil biological and functional attributes, which are often considered solely as barriers to restoration. This is problematic given that ecosystems' structure and function, and therefore their capacity to be self-sustaining, are underpinned by the strong linkages among plants, soils and the soil biota. Moreover, soil is a biological hotspot, with more than half of Earth's biodiversity being soil-borne. Here, we illustrate how soil biological and functional attributes can be used to guide restoration interventions, enhance restoration outcomes and complement vegetation-focused metrics for more comprehensive assessments of ecosystem condition and recovery. Importantly, soil biology can be managed to improve restoration outcomes and, under favourable conditions, enhance habitat suitability for threatened plant species. Future ecological restoration projects would thus benefit from explicitly considering soil biological and functional attributes.