Patterns and drivers of dark diversity in a eucalypt forest undergoing restoration after mining

Species absences can provide meaningful insights for ecological restoration. This ‘dark diversity’ can reveal species pools, the number and characteristics of suitable yet absent species, and the proportion of potential diversity realised (community completeness). Here, patterns in species richness, dark diversity, species pools and community completeness were assessed along a 25-year chronosequence of jarrah ( Eucalyptus marginata ) forest under restoration in southwestern Australia. Species were classified into plant functional types (PFTs) using a multi-trait approach to assess the functional analogues of the same metrics. A decline in species and functional richness over time corresponded with increased dark diversity and lower community completeness, and the composition of species and functional pools changed over time; however, whether these short-term trends are consistent with long-term succession patterns in the jarrah forest warrants further investigation. Variability detected among plots of the same age indicated that site and year effects influence the diversity and composition of species and functional pools. Restoration practices driving dark diversity affinity—the likelihood of species and PFTs being absent from suitable sites—were then assessed. Topsoil handling, fertilisation, the species richness of the applied seed mix and the timing of seeding emerged as influential. Species and PFTs absent from restoration plots remained members of the species and functional pools as dark diversity, suggesting that those plots maintain the potential to recruit missing species. This research exemplifies how dark diversity coupled with functional approaches can advance the monitoring and management of restoration.