Topsoil removal increases native forb and grass recovery in a southern Australian urban temperate grassland

Abstract Introduction Native temperate grasslands are globally threatened, biodiversity‐rich ecosystems. In urban post‐agricultural grasslands, restoration often achieves reestablishment of grass species‐dominated communities, yet associated forb recovery remains limited by non‐native seedbanks and nutrient‐enriched soils. Objectives We tested whether pre‐sowing interventions that target biomass, seedbanks, and soil nutrients can improve native plant recovery, especially forbs, in a degraded urban post‐agricultural grassland. Methods We ran a randomized complete block experiment (6 blocks × 5 treatments; n = 30 plots) comparing three types of treatments: (1) biomass removal alone via glyphosate application (chemical fallow; noting that herbicide use in restoration is subject to regional regulatory requirements and practitioner preferences); (2) soil solarization (6 and 12 weeks); and (3) topsoil removal (to 7 and 14 cm depth). We sowed 41 native plant species and surveyed vegetation at 6 (first growing season) and 18 months (second growing season) post‐sowing to quantify alpha diversity, community composition, and plant functional group responses. Results At 6 months, both topsoil removal depths had already elevated sown native alpha diversity above all other treatments. By 18 months, topsoil removal substantially increased total native and sown alpha diversity, with pronounced gains for forbs and strongly reduced non‐native grass dominance. The 12‐week solarization treatment also promoted total and sown native alpha diversity after 18 months, but benefits were largely confined to grasses, limiting whole‐community recovery. Conclusions Restoring forb‐rich grassland communities in nutrient‐enriched systems requires intensive soil reset (i.e. returning soil conditions toward those of reference native grassland) via topsoil removal. Seedbank‐focused (solarization) and biomass‐only (chemical fallow) interventions were insufficient to shift plant communities away from non‐native dominance.