Indicators for monitoring minesite rehabilitation: trends on waste-rock dumps, northern Australia

Minesite rehabilitation needs to be monitored with easily measured indicators so that trends can be plotted and assessed over time to address closure criteria. Our aim was to evaluate two traditional vegetation indicators used in woodlands and forests (tree composition and size), and two new landscape surface indicators (integrity of rip-lines and a nutrient cycling index), as well as a new habitat complexity index. We measured these five indicators on rehabilitated waste-rock dumps of differing ages on two mines in northern Australia, and compared these measures to those for nearby natural savannas. Our results confirm that tree composition and size were useful traditional indicators of vegetation development on rehabilitation because trends were towards that expected for nearby savannas. Surface roughness, as indicated by rip-lines, was also a useful indicator of the potential for a landscape to retain resources because these rip-lines persisted until vegetation was well established to assume this role. As this vegetation developed, soil surface condition, as indicated by a nutrient cycling index, also progressed towards values found on nearby natural savannas. A habitat complexity index suggested that older rehabilitation sites were developing the structural features needed by fauna. Although our findings need to be confirmed for other mines and for older sites, they do suggest that these five ecological indicators are useful for monitoring minesite rehabilitation.