A pioneer tree species rapidly facilitating ecosystem restoration in coastal regions depends on soil traits

The low-cost, ecologically friendly afforestation in coastal regions has been used to mitigate the natural degraded ecosystem. However, ecological consequences of this land use change are poorly known. We investigated the a short-term (2.5 years) effect of afforestation of a pioneer tree species, Casuarina equisetifolia, on understory vascular plants and surface soil traits (0–10 cm) at two closely-located sites (Heipaijiao and Haigui) in a subtropical coastal region, south China. Generally, plant abundance, vegetation coverage, and soil fertility in the natural degraded land were higher in Heipaijiao than in Haigui. After afforestation, the understory vascular plant abundance (increased by 46.1 %) and coverage (increased by 86.1 %) in Heipaijiao were recovered remarkably faster than those in Haigui; but there was slow recover in plant species composition, especially in Haigui. Owing to afforestation, soil water content and organic C (especially particulate organic C), electricity conductivity, Na+ and available K, and soil microbial biomass C increased but pH value decreased; the contents of total N, P and K, available N and P contents, and mineral-associated organic C had no great difference. Afforestation enhanced the richness, rather than alpha diversity, of soil bacteria and fungi. Soil microbes formed four spatially separated groups exhibiting overlapping and distinct microbial communities across different land-use types. Afforestation had a significant effect on the putative two-dominant functions of soil bacteria, i.e., soil C and N cycling. Thus, afforestation can maintain ecosystem multifunction quantified based on C sequestration, nutrient cycling and plant productivity. Understory plant recovery occurred faster than soil recovery; but no consistent restoration pattern existed for soil traits responded to afforestation. Recovery of understory plant and soil traits strongly depends on local soil conditions. This afforestation success story of selecting a well-adapted pioneer tree (C. equisetifolia) as foundation species provides insights into the restoration practice under harsh environmental conditions.