Faster recovery of soil biodiversity in native species mixture than in Eucalyptus monoculture after 60 years afforestation in tropical degraded coastal terraces

Afforestation is an effective method to restore degraded land. Afforestation methods vary in their effects on ecosystem multifunctionality, but their effects on soil biodiversity have been largely overlooked. Here, we mapped the biodiversity and functioning of multiple soil organism groups resulting from diverse afforestation methods in tropical coastal terraces. Sixty years after afforestation from bare land (BL), plant species richness and the abundance of plant litter (398 ± 85 g m⁻²) and plant biomass (179 ± 3.7 t ha⁻¹) in native tree species mixtures (MF) were restored to the level of native forests (NF; 287 ± 21 g m⁻² and 243.0 ± 33 t ha⁻¹, respectively), while Eucalyptus monoculture (EP) only successfully restored the litter mass (388 ± 43 g m⁻²) to the level of NF. Soil fertility in EP and MF was increased but remained lower than in NF. For example, soil nitrogen and phosphorus concentrations in MF (1.2 ± 0.2 g kg⁻¹ and 408 ± 49 mg kg⁻¹, respectively; p < 0.05) were lower than in NF (1.8 ± 0.2 g kg⁻¹ and 523 ± 24 mg kg⁻¹, respectively; p < 0.05). Soil biodiversity, abundance (except for nematodes), and community composition in MF were similar or greater than those in NF. In contrast, restoration with EP only enhanced the diversity of microbes and mites to the level of NF, but not for other soil biota. Together, afforestation with native species mixtures can end up restoring vegetation and most aspects of the taxonomic and functional biodiversity in soil whereas monoculture using fast-growing non-native species cannot. Native species mixtures show a greater potential to reach completely similar levels of soil biodiversity in local natural forests if they are received some more decades of afforestation. Multifunctionality of soil biotic community should be considered to accelerate such processes in future restoration practices.