Integrated analysis of aboveground and belowground indicators support a comprehensive evaluation of ecosystem recovery

Analyses of diverse aboveground and belowground indicators should underpin assessments of ecosystem recovery, yet monitoring many indicators is costly and their integration is challenging. Our objective was to combine indicators through a Bayesian hierarchical model to provide a comprehensive assessment of ecosystem status and identify a cost-effective subset of indicators to provide an accurate estimate of ecosystem recovery. We assessed 59 aboveground-belowground indicators, classified into nine components of composition, structure, and function, to estimate the ecosystem status of restored rock spoils and reference forests in south-eastern Australia. Overall ecosystem status, which integrates across ecosystem components and supporting indicators, was lower within restored forests but positively correlated with forest age. Reference forests had greater aboveground and belowground biotic structure, organic matter supply, and soil carbon stability, and trends were consistent among all of their supporting indicators. A subset of organic matter quality and nutrient cycling indicators were greater within restored forests, suggesting high ecosystem process rates, but that soil carbon may be more vulnerable to loss. Aboveground biotic structure was correlated with organic matter supply and quality, stability of soil carbon, the cycling of nutrients, and belowground biotic structure, providing evidence of aboveground-belowground coupling. A combination of four indicators representing belowground biotic structure, soil carbon stability, organic matter supply, and aboveground composition, provided a good estimate of ecosystem status at a third of the cost. Although ecosystem status can be monitored with a small set of indicators, a diversity of aboveground-belowground indicators provide a robust and comprehensive assessment of recovery.