Global meta-analysis reveals incomplete recovery of soil conditions and invertebrate assemblages after ecological restoration in agricultural landscapes

Restoration of old fields in agricultural landscapes has become increasingly important for conservation of species and their habitats owing to habitat destruction and rapid environmental change. Studies examining the outcomes of old field restoration predominantly focus on plant, and sometimes, vertebrate communities. Fewer studies have systematically investigated the effects of restoration efforts on soil properties or ground-dwelling invertebrates and there is limited synthesis of these data. We conducted a global meta-analysis of published studies to assess the effects of old field restoration on soil properties and soil invertebrate abundance and richness. We anticipated increased vegetation cover would improve soil properties towards reference condition and in turn, this would promote invertebrate abundance and richness. Studies were included if field sites had a history of cropping or livestock grazing. We identified 42 studies (1994-2019) from 16 countries that met our criteria. More studies assessed passive restoration methods than active planting, and native species were more commonly planted than exotic species. Results showed that restoration improved soil conditions with respect to total nitrogen, magnesium, soil carbon, bulk density and porosity when compared to controls; however, conditions similar to those in reference ecosystems were generally not achieved, even 50+ years after restoration had been initiated. Moderator analyses showed few significant tends, however, bulk density improved with age, and in passively restored versus reference ecosystems. Outcomes for soil carbon and bulk density were most predominant in the top soil when compared to the degraded ecosystem. We detected no consistent trends for the effect of restoration on soil invertebrate richness and abundance compared to the control or reference ecosystems. Synthesis and applications. Our global meta-analysis found strong evidence that old field restoration in agricultural landscapes had positive effects on soil condition but did not lead to full recovery when compared to a reference ecosystem. We detected few and idiosyncratic effects for invertebrates. Further research is needed to understand effects of restoration on soil invertebrate functional groups and to develop management interventions that accelerate the restoration of soil condition.