Site preparation impacts on soil biotic and abiotic properties, weed control, and native grass establishment

In severely degraded systems active restoration is required to overcome legacies of past land use and to create conditions that promote the establishment of target plant communities. While our understanding of the importance of soil microbial communities in ecological restoration is growing, few studies have looked at the impacts different site preparation techniques have on these communities. We trialed four methods of site preparation: fire, top-soil removal (TSR; removal of top 50 mm of soil), slashing (vegetation cut to 30 mm, biomass removed), and carbon (C; as sugar and saw-dust) addition, and quantified resulting soil bacterial communities using DNA metabarcoding. We compared the effectiveness of these techniques to reduce weed biomass, improve native grass establishment, and induce changes in soil nutrient availability. TSR was the most effective technique, leading to a reduction in both available nutrients and competition from weeds. In comparison, the remaining methods had little or no effect on weed biomass, native grass establishment, or soil nutrient availability. Both TSR and C addition resulted in changes in the soil bacterial community. These changes have the potential to alter plant community assembly in many ways, such as via nutrient acquisition, pathogenic effects, nutrient cycling, and decomposition. We recommend TSR for ecological restoration of old-fields and suggest it is a much more effective technique than burning, slashing, or C addition. Restoration practitioners should consider how their management techniques may influence the soil biota and, in turn, affect restoration outcomes.